DTC 5-1-1

5-1-1 LONG TERM FUEL TRIM, IDLING, LOWER LIMIT

Condition(s) for DTCs
^ The MFI module receives information from the Heated Oxygen Sensor (HO2S) if the air/fuel mixture is too rich in the idling range (5-1-1) or in the part-load range (2-3-1). In this case, the HO2S signal will usually be over 0.5 Volts. The MFI module short term fuel trim compensates for this by making the mixture leaner so as to maintain a value of Lambda = 1. Deviation of the short term fuel trim mid-setting from its normal value will be compensated by the long term fuel trim function. When the long term function approaches the lean mixture limit (lower limit), the MFI module will interpret the condition as abnormal and the DTC will be recorded.

Substitute value
^ None.

Fault source(s)
^ Contact resistance and oxidation in MAF sensor connector.
^ Faulty Mass Air Flow (MAF) Sensor.
^ High fuel pressure.
^ EVAP system leakage.
^ Contaminated engine oil.
^ High oil level.
^ Leaking injectors.

Fault symptom(s)
^ May cause high fuel consumption.
^ May cause impaired performance.

TESTING PROCEDURE





Other DTCs
^ Read other DTCs.

If MFI DTC 5-1-2 is recorded:
- Proceed to DTC 5-1-2 Short Term Fuel Trim, Lower Limit.
If MFI DTC 5-1-2 is not recorded:
- Check MAF sensor signal.





Checking MAF sensor signal
^ Switch ON ignition.
^ Connect voltmeter between sensor connector terminal 4 and ground.

Instrument should indicate approx. 2.8 Volts.

If reading is correct:
- Check engine oil level.
If reading is incorrect:
- Check sensor connector for contact resistance and oxidation.

^ Repeat above measurement after connector has been checked.

If reading is still incorrect:
- Check power ground.





Checking engine oil level
^ Switch OFF ignition.
^ Check engine oil level.

Level should be below max. mark on dipstick.

If level is correct:
- Check oil.
If level is incorrect:
- Adjust to correct level.





Checking engine oil
^ START engine and allow to idle for a few minutes.
^ Display DTC parameter list.
^ Read and note short term fuel trim (integrator) signal value.
^ Disconnect and plug crankcase ventilation outlet.
^ Recheck short term fuel trim signal value.

Value should remain more or less unchanged.

If value is correct:
- Check fuel pressure.
If value increases:
- Engine oil is diluted by fuel. Change oil and filter.





Checking fuel pressure
^ Switch OFF ignition.
^ Check fuel pressure and residual pressure as shown.

If fuel and residual pressure are correct:
- Check EVAP system.
If fuel and residual pressure are incorrect:
- Carry out repairs as required.





Checking EVAP system
^ Check EVAP system as described in EMISSION CONTROL SYSTEMS.

If system is operating correctly:
- Connect test box to MFI system and check ground terminals.
- Plug MFI module into test box adapter.
- Check all signals to and from MFI module.





Checking power ground
^ Switch OFF ignition.
^ Disconnect MAF sensor.
^ Connect ohmmeter between sensor connector terminal 2 and ground.

Instrument should indicate approx. 0 Ohms.

If reading is correct:
- Try with new sensor.
If reading is incorrect:
- Check ground terminals at rear of engine and associated wiring for contact resistance.
- Check MFI module connector for contact resistance.