DTC 2-2-1

2-2-1 LONG TERM FUEL TRIM, PART LOAD, UPPER LIMIT

Condition(s) for DTCs
^ The MFI module receives information from the Heated Oxygen Sensor (HO2S) if the air/fuel mixture is too lean in the idling range (2-3-2) or in the part-load range (2-2-1). In this case, the HO2S signal will usually be less than 0.5 Volts. The MFI module short term fuel trim compensates for this by enriching the mixture so 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. Enrichment by the long term almost to a maximum (upper limit) will be interpreted as abnormal and the DTC will be recorded.

Substitute value
^ None.

Fault source(s)
^ Open-circuit in HO2S heater supply or signal lead.
^ HO2S heater signal lead short-circuited to ground or supply.
^ Faulty HO2S.
^ Contact resistance and oxidation in HO2S connector.
^ Faulty MAF sensor.
^ Low fuel pressure.
^ Air leakage.
^ Incorrect sensor signals.

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

TESTING PROCEDURE





Other DTCs
^ Read other DTCs.

If MFI DTC 1-1-3 is recorded:
- Proceed to DTC 1-1-3 Short Term Fuel Trim, Upper Limit.
If MFI DTC 1-1-3 is not recorded:
- Check HO2S heater supply lead.





Checking HO2S heater supply lead, 2-pin connector
^ Switch ON ignition.
^ Disconnect HO2S heater connector (C/EF).
^ Connect voltmeter between HO2S heater connector (C/EF) terminal 1 (MFI module side) and ground.

Instrument should indicate battery voltage.





Checking HO2S heater supply lead, 4-pin connector
^ Switch ON ignition.
^ Disconnect HO2S.
^ Connect voltmeter between HO2S connector (C/EP) terminal 1 (MFI module side) and ground.

Instrument should indicate battery voltage.

If reading is correct:
- Check HO2S heater signal lead.
If reading is incorrect:
- Check lead between main relay (2/32) terminal 3 and HO2S connector terminal 1 (2-pin, C/EF or 4-pin, C/EP) for open-circuit.





Checking HO2S heater signal lead, 2-pin connector
^ Switch ON ignition.
^ Disconnect HO2S heater.
^ Connect voltmeter between HO2S heater connector (C/EF) terminal 2 (MFI module side) and ground.

Instrument should indicate approx. 2 Volts.





Checking HO2S heater signal lead, 4-pin connector
^ Switch ON ignition.
^ Disconnect HO2S.
^ Connect voltmeter between HO2S connector (C/EP) terminal 2 (MFI module side) and ground.

Instrument should indicate approx. 2 Volts.

If reading is correct:
- Check HO2S heater element.
If Instrument Indicates approx. 0 Volts:
- Check resistance of signal lead to ground.
If Instrument indicates over 5 Volts:
- Check lead between MFI module A28 and HO2S connector terminal 2 (2-pin, C/EF or 4-pin, C/EP) for short-circuit to supply.





Check resistance of signal lead to ground, 2-pin connector
^ Switch ON ignition.
^ Disconnect HO2S heater.
^ Connect ohmmeter between HO2S heater connector (C/EF) terminal 2 (MFI module side) and ground.





Check resistance of signal lead to ground, 4-pin connector
^ Switch ON ignition.
^ Disconnect HO2S.
^ Connect ohmmeter between HO2S connector (C/EP) terminal 2 (MFI module side) and ground.

If resistance is approx. 0 Ohms:
- Check lead between MFI module A28 and HO2S connector terminal 2 (2-pin, C/EF or 4-pin, C/EP) for short-circuit to ground.
If resistance is infinite (no continuity):
- Check lead between MFI module A28 and HO2S connector terminal 2 (2-pin, C/EF or 4-pin, C/EP) for open-circuit.





Checking HO2S heater element, 2-pin connector
^ Switch OFF ignition.
^ Disconnect HO2S heater.
^ Connect ohmmeter between HO2S heater connector (C/EF) terminals 1 and 2 (HO2S side).

Instrument should indicate 3 - 13 Ohms depending on temperature.





Checking HO2S heater element, 4-pin connector
^ Switch OFF ignition.
^ Disconnect HO2S.
^ Connect ohmmeter between HO2S connector terminals 1 and 2 (C/EP) (HO2S side).

Instrument should indicate 3 - 13 Ohms depending on temperature.

If reading is correct:
- Check MAF sensor signal.
If reading is incorrect:
- Try with new HO2S.





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

Instrument should indicate approx. 2.8 Volts.

If reading is correct:
- Check fuel pressure.
If reading is incorrect:
- Check MAF sensor connector for contact resistance and oxidation.

^ Repeat above measurement.

If reading is still incorrect:
- Check power ground.





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

If fuel pressure and residual pressure are correct:
- Check for air leakage.
If fuel pressure and residual pressure are incorrect:
- Correct as required.





Checking for air leakage
^ Check hoses and connections for air leakage.

If no leakage is present:
- 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 MAF sensor connector terminal 2 and ground.

Instrument should indicate approx. 0 Ohms.

If reading is correct:
- Try with new MAF 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.