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Home >> Dodge >> 1995 >> Avenger L4-2.0L DOHC >> Repair and Diagnosis >> Powertrain Management >> Computers and Control Systems >> Description and Operation >> On-Board Diagnostic System >> System Description

System Description






The Powertrain Control Module (PCM) monitors many different circuits in the fuel injection, ignition, emission and engine systems. If the PCM senses a problem with a monitored circuit often enough to indicate an actual problem, it stores a Diagnostic Trouble Code (DTC) in the PCM's memory.

MIL OPERATION
Self Test
As a functional test, the malfunction indicator lamp (MIL) illuminates at key-on before engine cranking.

Trouble Code Set MIL Operation
Whenever the Powertrain Control Module (PCM) sets a diagnostic trouble code that effects vehicle emissions, it illuminates the MIL.
- The PCM illuminates the MIL only for diagnostic trouble codes that effect vehicle emissions.
- The MIL remains on until the diagnostic trouble code is erased.
- On manual transaxle vehicles, the MIL either flashes or illuminates continuously when the PCM detects active engine misfire.
- During active misfire, the PCM records the current engine operating conditions. The engine operating conditions are recorded by the PCM.

NOTES:
1. After the Power Train Control Module (PCM) detects a malfunction, the check engine/malfunction indicator lamp illuminates when the engine is next turned on and the same malfunction is re-detected.

However, for items marked with a "*", the check engine/malfunction indicator lamp illuminates on the first detection of the malfunction.

After detecting a malfunction, if the PCM does not re-detect the malfunction for 40 drives*, the diagnostic trouble code will be erased from PCM memory.

NOTE: A "drive" indicates from engine start to stop and monitors powertrain components.

For misfiring or a fuel system rich/lean problem trouble codes will be erased when:
- Driving conditions (engine speed, engine coolant temperature, etc) are similar to those when the malfunction was first recorded.
- When the PCM does not re-detect the malfunction for 80 drives*.

2. After the check engine/malfunction indicator lamp illuminates, it will be switched off under the following conditions.
- When the ECM monitored the powertrain malfunction three times* and detected no malfunction.
*: In this case, one time indicates from engine start to stop.
- For misfiring or a fuel trim malfunction, when driving conditions (engine speed, engine coolant temperature, etc.) are similar to those when the malfunction was first recorded

ITEMS INDICATED BY THE CHECK ENGINE/MALFUNCTION INDICATOR LAMP
- No cam signal at PCM
- EGR solenoid circuit
- Injector #1 control circuit
- Injector #3 control circuit
- Idle air control motor circuit
- Throttle position sensor voltage high
- Engine coolant temperature sensor voltage too high
- No vehicle speed sensor signal
- MAP sensor voltage too high
- Ignition Coil No. 1 primary circuit
- No MFI relay (ASD) relay) output voltage at PCM
- Secondary air solenoid circuit
- Intake air temperature sensor voltage high
- PCM failed SPI communications
- High speed fan control relay circuit
- Upstream HO2S heater failure
- Internal Controller failure
- EVAP solenoid circuit
- Injector #2 control circuit
- Injector #4 control circuit
- Throttle position sensor voltage low
- Engine coolant temperature sensor voltage too low
- Upstream HO2S stays at center
- MAP sensor voltage too low
- No change in MAP from start to run
- Ignition Coil No. 2 primary circuit
- EGR system failure
- Intake air temperature sensor voltage low
- Upstream HO2S shorted to voltage
- Low speed fan control relay circuit
- Upstream HO2S response
- Downstream HO2S response
- Downstream HO2S heater failure
- Multiple cylinder misfire *
- Cylinder #1 misfire *
- Cylinder #2 misfire *
- Cylinder #3 misfire *
- Cylinder #4 misfire *
- Too little secondary air or too much secondary air
- Catalytic converter efficiency failure
- EVAP purge flow monitor failure
- Park/Neutral switch failure
- Power steering switch failure
- Fuel system rich*
- Fuel system lean*
- Downstream HO2S shorted to voltage
- Closed loop temperature not reached
- TPS voltage does not agree with MAP
- Target idle not reached (1200 r/min)
- Timing belt skipped 1 tooth or more
- Intermittent loss of camshaft position or crankshaft position

*, The check engine/malfunction indicator lamp illuminates on the first detection of the malfunction.

CAUTION: If the check engine/malfunction indicator lamp illuminates because of a malfunction of the PCM, transmission between the scan tool and the PCM cannot occur. In this case, the diagnostic trouble code cannot be read.

FREEZE FRAME DATA
The PCM records the diagnostic trouble code and also the engine operating conditions at the time the malfunction was detected.

This data is called "freeze frame" data.

Freeze frame data indicates the engine operating conditions from when nothing at all is detected to the initial detection of the malfunction.

However, misfiring or fuel trim malfunction data are always replaced with the latest data.

This data can be read by using the scan tool, and can then be used in simulation tests for troubleshooting.

Freeze Frame Data Items:
- Engine coolant temperature °C or °F
- Engine speed r/min. or RPM
- Vehicle speed km/h or mph
- Long-term fuel compensation (Long-term fuel trim)
- Short-term fuel compensation (Short-term fuel trim)
- Fuel control condition
Open loop
Closed loop
Open loop-Drive condition
Open loop-DTC set
Malfunction of closed loop-O2 (rear)
- Calculated load value
- MAP vacuum in.Hg (vacuum)
- Diagnostic trouble code during data recording
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