DTC 2-3-2

2-3-2 LONG TERM FUEL TRIM IDLING

Precondition for DTC
^ The control module receives information from the Heated Oxygen Sensor (HO2S) about the fuel/air mixture in the idling and partial load ranges. If the fuel/air mixture deviates from Lambda=1 the short term fuel trim will compensate this by adjusting the injection timing so that Lambda=1 is achieved. When the short term fuel trim carries out this adjustment, its mid-point must be adapted by the long term trim. When the long term fuel trim has adapted the short term trim to a maximum value, DTC 2-3-2 (idling range -0.48 ms to +0.40 ms) or DTC 2-3-1 (partial load range 0.773 to 1.227) and status message Upper Limit (lean fuel/air mixture) or Lower Limit (rich fuel/air mixture) will be set.

Substitute values
^ None.

Fault sources
^ Upper limit:
- Defective Mass Air Flow (MAF) sensor.
- Low fuel pressure.
- Air leakage.
- Faulty sensor signals.

^ Lower limit:
- Defective Mass Air Flow (MAF) sensor.
- Air leakage.
- High fuel pressure.
- Leaking injectors.
- Leaking EVAP system.
- Dirty engine oil.
- Oil level too high.
- Faulty sensor signals.

Fault symptoms
^ Can result in high fuel consumption.
^ Can result in impaired performance.

TESTING PROCEDURE





Other DTCs
^ Check for other DTCs

If DTC 3-1-5 is stored:
- See Testing By Trouble Code / DTC 3-1-5 EVAP system.
If DTC 3-1-5 is not stored:
- Check Status message.





Status Message
^ Check current status message.

If Status message is: Upper limit:
- Proceed to: UPPER LIMIT section below.
If Status message is: Lower limit:
- Proceed to: LOWER LIMIT section below.





UPPER LIMIT

Checking the MAF Sensor
^ Switch Ignition ON.
^ Connect a voltmeter between the MAF connectors 2 and 4.

The voltmeter shall show 0.1 - 0.2 Volts.

If the reading is OK:
- Check for air leakage in the intake system.
If the reading differs:
- Test with a new MAF sensor.





Checking Air Leakage in the Intake System
^ Check if there is any air leakage.
^ Check for air leakage in the intake system.

If there is no air leakage:
- Check for air leakage in the exhaust system.
If there is air leakage:
- Rectify as necessary, then clear DTCs and reset adaption.





Checking For Air Leakage in the Exhaust System
^ Check if there is any air leakage.
^ Check for air leakage in the exhaust system.

If there is no air leakage:
- Check fuel and residual pressure.
If there is air leakage:
- Rectify as necessary, then clear DTCs and reset adaption.





Checking Fuel And Residual Pressure
^ Check fuel and residual pressure.

If fuel and residual pressure are OK:
- Connect the break-out box.
If fuel and residual pressure are incorrect:
- Rectify as necessary, then clear DTCs and reset adaption.





Connecting the Break-Out Box
^ Connect the break-out box and check the ground connectors.
^ Connect the ECM.
^ Check all the signals to and from the ECM.
^ Rectify as necessary, then clear DTCs and reset adaption.

LOWER LIMIT





Checking the MAF Sensor
^ Switch Ignition ON.
^ Connect a voltmeter between MAF sensor connectors 2 and 4.

The voltmeter should show 0.1 - O.2 Volts.

If the reading is OK:
- Check for air leakage of the intake system.
If the reading differs.
- Test with a new MAF sensor.





Check for Air Leakage in the Intake System
^ Check if there is any air leakage.

If there is no leakage:
- Check for air leakage in the exhaust system.
If there is air leakage:
- Rectify as necessary. Then clear DTCs and adaption.





Checking for Air Leakage in the Exhaust System
^ Check if there is any air leakage.

If there is no air leakage:
- Check for fuel and residual pressure.
If there is air leakage:
- Rectify as necessary. Then clear DTCs and adaption.





Checking Fuel and Residual Pressure
^ Check fuel and residual pressure.

If fuel and residual pressure are OK:
- Check the EVAP valve.
If fuel and residual pressure are incorrect:
- Rectify as necessary. Then clear DTCs and reset adaption.





Checking the EVAP Valve
^ Remove the hose leading to the intake manifold from the EVAP valve.
^ Refit the hose after fault tracing.
^ For re-installation, use pliers 981 4215 and a new hose clamp.
^ Connect vacuum pump 999 5843 to the EVAP valve coupling.
^ Pump a vacuum;

The vacuum meter should show stable vacuum.

If the valve is OK:
- Check the engine oil level.
If the valve is leaking:
- Test with a new EVAP valve. Then clear DTCs and reset adaption.





Checking the Engine Oil Level
^ Check the engine's oil level.

The oil level should be between the min. and max. markings.

If the oil level is OK:
- Check the engine oil.
If the oil level is incorrect:
- Fill to the correct oil level.
- Then continue with: Checking the engine oil.





Checking the Engine Oil
^ START the engine and let it run at idling speed for a few minutes.
^ Look up the DTC parameter.





^ Read off the value on the short term fuel trim and note the value.
^ Disconnect and plug the crankcase ventilation.
^ Read off the value of the short term fuel trim once again.

The value should remain more or less unchanged.

If the value is OK:
- Connect measuring instrument.
If the value rises:
- This indicates that the engine oil is diluted with fuel.
- Change the oil and oil filter. Then clear DTCs and reset adaption.





Connecting the Break-Out Box
^ Connect the break-out box and check the ground connectors.
^ Connect the ECM.
^ Check all the signals to and from the ECM.
^ Rectify as necessary, then clear DTCs and reset adaption.