DTC 2-1-2

2-1-2 HEATED OXYGEN SENSOR (HO2S) SIGNAL

Condition(s) for DTC
^ The DTC is recorded if the HO2S signal does not vary from its mid-value (0.45-0.46 V) within 3 minutes after the engine temperature has exceeded 80°C (175°F).

Substitute value
^ The integrator is set to mid-range and the fuel trim function is inhibited.

Fault source(s)
^ Open-circuit in signal lead.
^ Faulty HO2S heater.
^ Faulty HO2S.

Fault symptom(s)
^ Fuel consumption may be high.

TESTING PROCEDURE





Status message
^ Check current Status Message.

If Status Message is: Permanent fault, signal faulty:
- Proceed to PERMANENT FAULT, SIGNAL FAULTY Section below.
If Status Message is: Intermittent fault, signal faulty:
- Proceed to INTERMITTENT FAULT, SIGNAL FAULTY Section below.

PERMANENT FAULT, SIGNAL FAULTY





Checking HO2S heater supply lead 2-pin connector
^ Switch ON ignition.
^ Disconnect HO2S heater connector (C/EP).
^ Connect voltmeter between HO2S heater connector (C/EP) 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/EP 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/EP) 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 MFl module A28 and HO2S connector terminal 2 (2-pin, C/EP or 4-pin, C/EP) for short-circuit to supply.





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





Checking resistance of signal lead to ground, 4-pin connector
^ Switch OFF 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/EP 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/EP 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/EP) 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 (C/EP) terminals 1 and 2 (HO2S side).

Instrument should indicate 3 - 13 Ohms depending on temperature.

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





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

Instrument should indicate approx. 0.5 Volts.





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

Instrument should indicate approx. 0.5 Volts.

If reading is correct:
- Check HO2S.
If reading is approx. 0 Volts:
- Check lead between HO2S connector terminal 2 (2-pin, C/EP) or terminal 4 (4-pin, C/EP) and MFI module A22 for open-circuit.

^ Following repair of lead, check that HO2S is operating correctly.
^ Display DTC parameter list and read HO2S voltage.

Value should oscillate between 0.1 - 0.9 Volts with HO2S in circuit and hot, with engine idling.





Checking HO2S
^ Connect HO2S.
^ START engine.
^ Display DTC parameter list.
^ Read HO2S signal value.

Value should oscillate between approx. 0.1 and 0.9 Volts when HO2S is hot.

If reading is correct:
- DTC is due to poor contact in connector at HO2S. Check that connector pins are undamaged.
If reading does not oscillate:
- Try with new HO2S.

Note: HO2S connectors must not be packed with grease.

INTERMITTENT FAULT, FAULTY SIGNAL





Checking wiring and connections

Note: HO2S connectors must not be packed with grease.

^ Check lead between main relay (2/32) terminal 3 and HO2S connector terminal 1 (2-pin, C/EP or 4-pin, C/EP) for intermittent open-circuit.
^ Check lead between MFI module A28 and HO2S connector terminal 2 (2-pin, C/EP or 4-pin, C/EP) for intermittent open-circuit, intermittent short-circuit to ground or intermittent short-circuit to supply.
^ Check HO2S and MFI module connectors for loose connections.
^ Check lead between MFI module A22 and HO2S connector terminal 2 (2-pin, C/EP) or terminal 4 (4-pin, C/EP) for intermittent open-circuit.