Standard, 5 element alpha-numeric format, trouble codes, made up as follows:
Letter prefix defines system designation
B = BODY
C = CHASSIS
P = Powertrain
U = Network communications systems
First digit defines code type
0 = Standart EOBD
1 = Defined by vehicle manufacturer
2 = Standart EOBD
3 = Standart EOBD/defined by manufacturer
Second digit defines system identification
0 = Standart code (refer to P0 code list)
1 = Fuel or air
2 = Fuel or air
3 = Ignition
4 = Emission control
5 = Speed control (idle, vehicle etc.)
6 = Trip computer
7 = Transmission
8 = Transmission
9 = Transmission
Third and fourth digits define specific fault
These digits define general malfunction, range or performance of component or system, low or high input
Example code POl08
This code is logged when a high input is detected in the pressure circuit of the manifold absolute pressure (MAP) sensor or barometric pressure (BARO) sensor.
P = System - Powertrain
0 = Code type - EOBD
1 = System identification (fuel or air) - manifold absolute pressure (MAP) sensorlbarometric pressure (BARO) sensor.
0 = Pressure circuit
8 = High input
NOTE: Emissions related problems have a IS0 defined list of codes and definitions starting with P0001.
Standard areas monitored:
The following areas are monitored continuously:
- Misfire detection
- Fuel system performance
- Component performance
The following areas are monitored once per 'trip'
NOTE: The definition of a 'trip' varies, but is basically - key ON, vehicle driven, key OFF.
- Catalytic converter
- Evaporative emission system
- Secondary air (AIR) system
- Air conditioning system
- Heated oxygen sensor (H02S)
- Oxygen sensor (02s) heater
- Exhaust gas recirculation (EGR) system
- In cases where flash codes and EOBD codes are listed for the same model range, only one flash code will be generated for a particular component, but there may be a list of many EOBD codes related to this component. Alternatively there may be some EOBD codes with no equivalent flash code(s).
- These EOBD codes will provide more specific details about the fault location, wiring, voltage signals and other information relative to the circuit or system.
Logging faults with EOBD
- Fault logging is based on inputs received during each 'trip' which may comprise a number of 'drive cycles'.
- Each 'drive cycle' is initiated when the engine is started and is terminated when the engine is switched off.
- For a complete 'trip' to be completed the following, complex, conditions need to be met (and may take several 'drive cycles' to complete):
- This ensures that the ECM logs a cold start.
- Allow engine to idle for 2-3 minutes with an electrical load switched on (such as headlamps or heated rear window).
- This will ensure that the misfire monitoring and fuel trim monitoring programmes run.
- Drive vehicle up to at least 50 mph and maintain this speed for at least 3 minutes.
Misfire and fuel trim monitoring will run.
- Allow the speed to reduce to around 20 mph without changing gear, using the brakes or the clutch.
- Fuel trim monitoring will run.
- Accelerate to at least 50 mph and maintain for at least 5 minutes.
- Misfire and fuel trim monitoring will run.
- Allow the speed to reduce to around 20 mph without changing gear, using the brakes or the
clutch.
- Fuel trim monitoring will run.
- Each 'trip' starts when the engine is started and continues through a number of 'drive cycles' until all the EOBD monitors have completed a self-test.
- The EOBD monitoring programme provides operating tolerance checks on all emissions related sensors and actuators. Some components/circuits are continuously monitored and some are only activated under predetermined operating conditions.
- Misfire monitoring detects irregularities in the crankshaft position (CKP) sensor signal pattern and identifies which cylinder misfired and if the misfire is frequent enough to cause catalytic converter damage due to excess internal temperatures. If this is the case the MIL will flash.
- If the misfire is likely to increase emissions above the EOBD limits and occurs on each of two consecutive 'trips' the MIL will flash. If the misfire is absent during the next three 'trips' the MIL will be extinguished.
- When a fault code is logged a number of data parameters are stored with it, to assist in accurate fault diagnosis. These are:
- Vehicle speed
- Engine coolant temperature
- Engine rpm
- Engine load
- Oxygen sensor system status - open/closed loop
- Distance since fault first logged
- Long term fuel trim (LTFT) level
- Most EOBD scan tools are capable of capturing this 'snapshot' of data and displaying (or printing) it for analysis to aid the fault diagnosis process.
After rectification
- EOBD monitoring is very sensitive and replacement components may still be identified as faulty if their specifications do not exactly match the originals.
- The trouble code memory must be completely erased and a 'trip' completed.
- The trouble code memory should be accessed to establish that no further codes have been logged.
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