SCAN TOOL DIAGNOSTICS
A scan tool is also known as OBD interface,code reader,or an OBD scanner.
OBD is a computer based system found on most vehicles,whose main job is to keep tabs on the emission levels.
Over the years,OBD systems grew more sophisticated,and today can provide access to hundreds of vehicle parameters.
Most cars today have an OBD 1 and 2 systems,and are therefore compatible with the scan tools.
A scan tool is a device used to access on board diagnostic information.Scan tools come in many shapes and sizes,different brands.But there are two basic types :Stand Alone and PC based.As the name suggests,stand alone scan tools do not require a computer.However,they typically have a small screen with a miniature interface,run only proprietary software with limited functionality,and cost significantly more then comparable PC based scan tools.
PC based scan tools harness the power and economy of scale of modern PC's,and have a number of important advantages:
*Large.easy-to-read screen
*Unlimited storage for data logging
*Wide selection of diagnostic software that can be easily updated.
*Remote data acquisition
*Cost a small fraction of the cost of comparable stand-alone scan tools.
PC based scan tools can:
*Turn OFF the check engine light,and erase stored diagnostic information
*Check emissions readiness
*Read and erase trouble codes (generic and manufactures-specific)
*Display real time parameters
*Record data for later playback.
*Plot data in the form of graphs and maps.
*Display customizable Digital Gauges.
*Serve as a dynamo meter.
*Provide a drag strip feature.
*Generate printable diagnostic reports.
*Access manufacturer's diagnostic reports.
*Do lots of other cool and useful things
Information from:ScanTool.net
Some cheap scanners are not able to read faults on new European cars.They are not compatible
Some countries have free scanning.They charge for the job and scan for free.One example is Korea
Recently i was working on a Mitsubishi Pajero diesel.It had the ABS light ON.We plugged in the scanner.There was no fault codes.Everything looked fine.But after 30 seconds the ABS light kept coming ON.The scanner showed no fault codes.
Then after driving the van the scanner picked up a fault.It faulted a speed sensor.
We did find the fault eventually.
The scan was being done when the van was parked on the ground.
When we inspected the van on the hoist,we found a lot of movement on the wheel hub.The van had faulty wheel bearings.That's why the scanner picked up a fault on the speed sensor.
Maybe there was too much play in the wheel bearing.
After 2 brand new wheel bearings on each hub,the ABS light was OFF.
The van drove really smooth.
This is an example on how a mechanical fault can cause a fault at a sensor and would cause 1 of the safety lights to turn ON.
....................................................................................................................................................................
Type of information Letters to Value of Units for
(PID=Parameter describe it data data
Identification) E.g.TPS E.g.volts
.....................................................................................................................................................................
Engine Load MAP 2.58 gm/s
(how much air comes in)
.....................................................................................................................................................................
Engine RPM CRA 667 RPM
.....................................................................................................................................................................
Throttle angle TPS 10 %
.....................................................................................................................................................................
Engine coolant ECT 75 C
temperature
.....................................................................................................................................................................
Intake Air IAT 20 C
temperature
.....................................................................................................................................................................
Fuel Injection FIP 2.4 ms
opening pulse
.....................................................................................................................................................................
Vehicle Speed VSS 0 km/h
.....................................................................................................................................................................
Oxygen sensor(s) o2 0.52 V
.....................................................................................................................................................................
Fuel Trim FT -2.3 %
.....................................................................................................................................................................
Idle control ON
....................................................................................................................................................................
Air condition AC
.....................................................................................................................................................................
Malfunction Indicator ON
Light (MIL)
.....................................................................................................................................................................
5.Find What Data Has Changed
5.1 Look through the scan tool data to see what PIDs
(Parameter Identification of system voltages) have changed.
Which readings don't make sense or don't read what you would expect.
Concentrate on the PIDs related to the codes:
5.2 Record the PIDs that have changed below:
...................................................................................................................................
Type of information Letters to Value of Units for
(PID=Parameter describe it data data
Identification)
...................................................................................................................................................................
Intake Air Temperature IAT
....................................................................................................................................
Mass Air Flow MAF 0 gm/s
.....................................................................................................................................
Short Term Fuel Trim STFT 12.5 %
...................................................................................................................................
Throttle Position TPS 0 %
..................................................................................................................................
6. Visual Inspection to find fault
6.1 Do a visual inspection under the hood to find where the problem is.Use information from the code to know where to look for the problem and what type of problem to look for.
Describe the problem you found:
* The TPS sensor was not plugged in
7.Repair fault
7.1 Plug back in the connector,or repair problem found
7.2 Describe what you did
8.Re-check Data PIDs
8.1 Re-check the data with the scan tool
8.2 Record the voltages for the PIDs related to the problem,to confirm they are back to normal
...................................................................................................................................................................
Type of information Letters to Value of Units for
(PID=Parameter describe it data data
identification)
....................................................................................................................................................................
Intake Air temperature IAT 27 C
.....................................................................................................................................................................
Mass Air flow sensor MAF 2.58 gm/s
....................................................................................................................................................................
Short Term Fuel Trim STFT -2.3 %
.....................................................................................................................................................................
Throttle Position TPS 10 %
.....................................................................................................................................................................
9.Clear codes
Describe what you did to clear the codes:
*Used the scan tool to erase the fault
*Some codes get erased by itself.The ECU doesn't the fault anymore,so it clears the code.
10.Re-check for codes and record codes in system now:
*There are no fault codes in the system.The system is back to normal.
WS4 Fuel Pressure and flow (Petrol only)
Fuel is the means from which most of today's engines derive the energy to operate.But as the fuel deposits are being depleted,alternative fuel sources are being found.
Some alternatives are the electric hybrid cars,solar powered engines.
But petrol and diesel are the most widely used fuel today.Most commercial vehicles are diesel.
And most private passenger cars are petrol driven
Petrol engines are SI(Spark Ignition)
Diesel Engines are CI(Compression Ignition)
Most new vehicles use a electric fuel pump.The function of the fuel pump is to pump fuel at pressure to the injectors.The injectors are controlled by the the ECU.Each time the injectors open the fuel is sprayed into the combustion chamber at high pressure.
Some older cars used to have a mechanical fuel pump.The pump is mounted on the valve cover.And is operated by the cam lobes.These worked quite well.Till the EFI was introduced.And then came the electric pump.And then slowly as the technology improved,much powerful and compact electric pumps were designed to meet the high demands of the current modern engine.
MAKE:TOYOTA
ENGINE:4A-FE
These Toyota engines are very simple.
Very easy to identify the parts.
The parts are not expensive.
The engine is simple to work on.
They are good and reliable motors.
And very economical.
Locate the two closest fire extinguishers.
There were fire extinguishers mounted on the wall near the doors.On the right hand side of the doors.
And there were also signs and instructions on what to do in case of an emergency.
All the fire extinguishers had the valid stickers.
All the petrol engines that we worked on in the class were Toyota engines.That's the 4A-FE engines.Most of these engines had the manual with them.
We checked the Fuel Pressure Specification for this engine.
265-304kPa
C2.7-3.1 kgf/cm2
38-44 psi
Measure the fuel pressure with the key ON,engine OFF.
240 kPa
Idling:Measure the fuel pressure with the engine idling.Watch the pressure for a couple of minutes.
The pressure reading we got was 250 psi.
Maximum:With the engine idling,use the special tool to clamp the fuel return line.
This should only be done for a short period.
The reading we got was over 600 psi.
WOT:With the engine idling,disconnect and plug the vacuum line going to the fuel regulator
The pressure reading that we got was 310 kPa.
Residual:Turn OFF the engine,and watch the fuel pressure for five minutes.
The residual or the rest pressure we reading that we got was 270 kPa
Flow:Hook up proper equipment to read fuel volume.
Record flow gauge results of volume,or how much fuel pumped in 15 seconds.
Used a orange plastic clamp to block the fuel inlet hose.
Once the hose was blocked,we loosened and removed the hose clamp.
Once the clamp was removed,it was easier to remove the t hose.
We removed the inlet hose.And cranked the engine.
We managed to collect 690 ml of fuel in 15 seconds.
*(the results should be about 500 ml in 15 seconds)
This test result proves that this is a good fuel pump.It has normal pressure according to the manufactures specification.
*We put the fuel that we had collected back in the fuel tank.
*The petrol kept in an open container will give off harmful fumes.The fumes can cause headache and dizziness,which can cause a person to fall on a running engine and injury can be caused.
Replaced the fuel hose back.
Tightened the hose clamp.
It was tight.
Started the engine.Checked for any leaks.There was no leak.
There was no smell of petrol anywhere also.
The engine was running fine.
It is very important to know the vehicle fuel flow/pressure.
If the fuel pressure is low,the injectors will not get the required amount of fuel at the required pressure.
So instead of spraying pressurised fuel into the combustion chamber,there could just be drips of fuel.And this won't ignite in the normal pattern.
This could cause the engine to rough idle.
Also the engine will lack power.Especially on the motor ways when the engine requires more full because the vehicle is travelling at high speed.
The engine may start normally,but it won't run normal
Describe the symptoms a vehicle would give with each case:
Low fuel pressure:
The engine will not work normal.
It will lack power.
The engine may start easily.And it may idle normal.
But the real test is when the vehicle is being driven.As the vehicle is being accelerated,the need for more fuel increases.This is when the fuel pump is under load.And the fuel pump has to work hard to maintain the constant amount of fuel to the injectors.If the fuel pump is in the dying stage,then the vehicle would get sudden jerks.This is because the fuel pump cannot maintain a constant supply of fuel to the injectors.
Low fuel flow:
Low fuel flow is a sign of a blocked fuel filter.That's the first thing to check when you have low fuel flow.
Also there could be debris in the fuel line.
Maybe the container used to fill in the fuel in the fuel tank wasn't clean.And all the dirt and other rough particles could have gone in the fuel tank and blocking the fuel line.
Also there could be a dent or a puncture on the fuel line.This can happen if the vehicle drives over something big,or the vehicle is driven in quite deep puddles.
High fuel pressure:
If the fuel pressure is too high,it could damage the injectors.The original injectors on an engine is designed to handle a certain amount of pressure.And if the fuel pump was changed and the new fuel pump isn't of the manufacturer's specification,and is of a higher pressure value,then this could damage the injectors.
High fuel pressure is good for high performance engines.This is because the high performance engines require more fuel to burn at a much faster rate so it can go faster.But these engines also have high pressure injectors that can handle the high pressure fuel supplied by the fuel pump.
Faulty fuel pressure regulator:
There can be multiple issues with a faulty fuel pressure regulator.It could be open all the time.
Or it could be shut all the time.
Or it could have an intermittent issue,where it could just shut off while the vehicle is still being driven.
If it's shut all the time,then the car will not start at all.
If the fuel regulator is playing up,then the engine will have late starts.
The engine could just shut off while the vehicle is being driven.
The engine idle would play up.
The engine would stall all the time.
A scan tool is also known as OBD interface,code reader,or an OBD scanner.
OBD is a computer based system found on most vehicles,whose main job is to keep tabs on the emission levels.
Over the years,OBD systems grew more sophisticated,and today can provide access to hundreds of vehicle parameters.
Most cars today have an OBD 1 and 2 systems,and are therefore compatible with the scan tools.
A scan tool is a device used to access on board diagnostic information.Scan tools come in many shapes and sizes,different brands.But there are two basic types :Stand Alone and PC based.As the name suggests,stand alone scan tools do not require a computer.However,they typically have a small screen with a miniature interface,run only proprietary software with limited functionality,and cost significantly more then comparable PC based scan tools.
PC based scan tools harness the power and economy of scale of modern PC's,and have a number of important advantages:
*Large.easy-to-read screen
*Unlimited storage for data logging
*Wide selection of diagnostic software that can be easily updated.
*Remote data acquisition
*Cost a small fraction of the cost of comparable stand-alone scan tools.
PC based scan tools can:
*Turn OFF the check engine light,and erase stored diagnostic information
*Check emissions readiness
*Read and erase trouble codes (generic and manufactures-specific)
*Display real time parameters
*Record data for later playback.
*Plot data in the form of graphs and maps.
*Display customizable Digital Gauges.
*Serve as a dynamo meter.
*Provide a drag strip feature.
*Generate printable diagnostic reports.
*Access manufacturer's diagnostic reports.
*Do lots of other cool and useful things
Information from:ScanTool.net
Some cheap scanners are not able to read faults on new European cars.They are not compatible
Some countries have free scanning.They charge for the job and scan for free.One example is Korea
Recently i was working on a Mitsubishi Pajero diesel.It had the ABS light ON.We plugged in the scanner.There was no fault codes.Everything looked fine.But after 30 seconds the ABS light kept coming ON.The scanner showed no fault codes.
Then after driving the van the scanner picked up a fault.It faulted a speed sensor.
We did find the fault eventually.
The scan was being done when the van was parked on the ground.
When we inspected the van on the hoist,we found a lot of movement on the wheel hub.The van had faulty wheel bearings.That's why the scanner picked up a fault on the speed sensor.
Maybe there was too much play in the wheel bearing.
After 2 brand new wheel bearings on each hub,the ABS light was OFF.
The van drove really smooth.
This is an example on how a mechanical fault can cause a fault at a sensor and would cause 1 of the safety lights to turn ON.
....................................................................................................................................................................
Type of information Letters to Value of Units for
(PID=Parameter describe it data data
Identification) E.g.TPS E.g.volts
.....................................................................................................................................................................
Engine Load MAP 2.58 gm/s
(how much air comes in)
.....................................................................................................................................................................
Engine RPM CRA 667 RPM
.....................................................................................................................................................................
Throttle angle TPS 10 %
.....................................................................................................................................................................
Engine coolant ECT 75 C
temperature
.....................................................................................................................................................................
Intake Air IAT 20 C
temperature
.....................................................................................................................................................................
Fuel Injection FIP 2.4 ms
opening pulse
.....................................................................................................................................................................
Vehicle Speed VSS 0 km/h
.....................................................................................................................................................................
Oxygen sensor(s) o2 0.52 V
.....................................................................................................................................................................
Fuel Trim FT -2.3 %
.....................................................................................................................................................................
Idle control ON
....................................................................................................................................................................
Air condition AC
.....................................................................................................................................................................
Malfunction Indicator ON
Light (MIL)
.....................................................................................................................................................................
5.Find What Data Has Changed
5.1 Look through the scan tool data to see what PIDs
(Parameter Identification of system voltages) have changed.
Which readings don't make sense or don't read what you would expect.
Concentrate on the PIDs related to the codes:
5.2 Record the PIDs that have changed below:
...................................................................................................................................
Type of information Letters to Value of Units for
(PID=Parameter describe it data data
Identification)
...................................................................................................................................................................
Intake Air Temperature IAT
....................................................................................................................................
Mass Air Flow MAF 0 gm/s
.....................................................................................................................................
Short Term Fuel Trim STFT 12.5 %
...................................................................................................................................
Throttle Position TPS 0 %
..................................................................................................................................
6. Visual Inspection to find fault
6.1 Do a visual inspection under the hood to find where the problem is.Use information from the code to know where to look for the problem and what type of problem to look for.
Describe the problem you found:
* The TPS sensor was not plugged in
7.Repair fault
7.1 Plug back in the connector,or repair problem found
7.2 Describe what you did
8.Re-check Data PIDs
8.1 Re-check the data with the scan tool
8.2 Record the voltages for the PIDs related to the problem,to confirm they are back to normal
...................................................................................................................................................................
Type of information Letters to Value of Units for
(PID=Parameter describe it data data
identification)
....................................................................................................................................................................
Intake Air temperature IAT 27 C
.....................................................................................................................................................................
Mass Air flow sensor MAF 2.58 gm/s
....................................................................................................................................................................
Short Term Fuel Trim STFT -2.3 %
.....................................................................................................................................................................
Throttle Position TPS 10 %
.....................................................................................................................................................................
9.Clear codes
Describe what you did to clear the codes:
*Used the scan tool to erase the fault
*Some codes get erased by itself.The ECU doesn't the fault anymore,so it clears the code.
10.Re-check for codes and record codes in system now:
*There are no fault codes in the system.The system is back to normal.
WS4 Fuel Pressure and flow (Petrol only)
Fuel is the means from which most of today's engines derive the energy to operate.But as the fuel deposits are being depleted,alternative fuel sources are being found.
Some alternatives are the electric hybrid cars,solar powered engines.
But petrol and diesel are the most widely used fuel today.Most commercial vehicles are diesel.
And most private passenger cars are petrol driven
Petrol engines are SI(Spark Ignition)
Diesel Engines are CI(Compression Ignition)
Most new vehicles use a electric fuel pump.The function of the fuel pump is to pump fuel at pressure to the injectors.The injectors are controlled by the the ECU.Each time the injectors open the fuel is sprayed into the combustion chamber at high pressure.
Some older cars used to have a mechanical fuel pump.The pump is mounted on the valve cover.And is operated by the cam lobes.These worked quite well.Till the EFI was introduced.And then came the electric pump.And then slowly as the technology improved,much powerful and compact electric pumps were designed to meet the high demands of the current modern engine.
MAKE:TOYOTA
ENGINE:4A-FE
These Toyota engines are very simple.
Very easy to identify the parts.
The parts are not expensive.
The engine is simple to work on.
They are good and reliable motors.
And very economical.
Locate the two closest fire extinguishers.
There were fire extinguishers mounted on the wall near the doors.On the right hand side of the doors.
And there were also signs and instructions on what to do in case of an emergency.
All the fire extinguishers had the valid stickers.
All the petrol engines that we worked on in the class were Toyota engines.That's the 4A-FE engines.Most of these engines had the manual with them.
We checked the Fuel Pressure Specification for this engine.
265-304kPa
C2.7-3.1 kgf/cm2
38-44 psi
Measure the fuel pressure with the key ON,engine OFF.
240 kPa
Idling:Measure the fuel pressure with the engine idling.Watch the pressure for a couple of minutes.
The pressure reading we got was 250 psi.
Maximum:With the engine idling,use the special tool to clamp the fuel return line.
This should only be done for a short period.
The reading we got was over 600 psi.
WOT:With the engine idling,disconnect and plug the vacuum line going to the fuel regulator
The pressure reading that we got was 310 kPa.
Residual:Turn OFF the engine,and watch the fuel pressure for five minutes.
The residual or the rest pressure we reading that we got was 270 kPa
Flow:Hook up proper equipment to read fuel volume.
Record flow gauge results of volume,or how much fuel pumped in 15 seconds.
Used a orange plastic clamp to block the fuel inlet hose.
Once the hose was blocked,we loosened and removed the hose clamp.
Once the clamp was removed,it was easier to remove the t hose.
We removed the inlet hose.And cranked the engine.
We managed to collect 690 ml of fuel in 15 seconds.
*(the results should be about 500 ml in 15 seconds)
This test result proves that this is a good fuel pump.It has normal pressure according to the manufactures specification.
*We put the fuel that we had collected back in the fuel tank.
*The petrol kept in an open container will give off harmful fumes.The fumes can cause headache and dizziness,which can cause a person to fall on a running engine and injury can be caused.
Replaced the fuel hose back.
Tightened the hose clamp.
It was tight.
Started the engine.Checked for any leaks.There was no leak.
There was no smell of petrol anywhere also.
The engine was running fine.
It is very important to know the vehicle fuel flow/pressure.
If the fuel pressure is low,the injectors will not get the required amount of fuel at the required pressure.
So instead of spraying pressurised fuel into the combustion chamber,there could just be drips of fuel.And this won't ignite in the normal pattern.
This could cause the engine to rough idle.
Also the engine will lack power.Especially on the motor ways when the engine requires more full because the vehicle is travelling at high speed.
The engine may start normally,but it won't run normal
Describe the symptoms a vehicle would give with each case:
Low fuel pressure:
The engine will not work normal.
It will lack power.
The engine may start easily.And it may idle normal.
But the real test is when the vehicle is being driven.As the vehicle is being accelerated,the need for more fuel increases.This is when the fuel pump is under load.And the fuel pump has to work hard to maintain the constant amount of fuel to the injectors.If the fuel pump is in the dying stage,then the vehicle would get sudden jerks.This is because the fuel pump cannot maintain a constant supply of fuel to the injectors.
Low fuel flow:
Low fuel flow is a sign of a blocked fuel filter.That's the first thing to check when you have low fuel flow.
Also there could be debris in the fuel line.
Maybe the container used to fill in the fuel in the fuel tank wasn't clean.And all the dirt and other rough particles could have gone in the fuel tank and blocking the fuel line.
Also there could be a dent or a puncture on the fuel line.This can happen if the vehicle drives over something big,or the vehicle is driven in quite deep puddles.
High fuel pressure:
If the fuel pressure is too high,it could damage the injectors.The original injectors on an engine is designed to handle a certain amount of pressure.And if the fuel pump was changed and the new fuel pump isn't of the manufacturer's specification,and is of a higher pressure value,then this could damage the injectors.
High fuel pressure is good for high performance engines.This is because the high performance engines require more fuel to burn at a much faster rate so it can go faster.But these engines also have high pressure injectors that can handle the high pressure fuel supplied by the fuel pump.
Faulty fuel pressure regulator:
There can be multiple issues with a faulty fuel pressure regulator.It could be open all the time.
Or it could be shut all the time.
Or it could have an intermittent issue,where it could just shut off while the vehicle is still being driven.
If it's shut all the time,then the car will not start at all.
If the fuel regulator is playing up,then the engine will have late starts.
The engine could just shut off while the vehicle is being driven.
The engine idle would play up.
The engine would stall all the time.
