DTC 2-1-2

2-1-2 HEATED OXYGEN SENSOR SIGNAL




Trouble Code Conditions
If sensor voltage constantly exceeds 1.1 volts (signal too high): constantly lies below 0.09 volts (signal too low): or if the sensor voltage does not deliver its average 0.5 volts (signal absent) 3 minutes after the engine temperature has reached 75°C (167°F) and a certain amount of load has been experienced, Diagnostic Trouble Code (DTC) 2-1-2 is set.

Substitute value(s)
- Fuel trim inhibited.

Fault source(s)
Signal too high:
- Signal lead short circuited to live.
- Defective Heated Oxygen Sensor (HO2S).

Signal too low:
- Signal lead short circuited to ground.
- Defective heated oxygen sensor.
- Air leakage or fuel pressure too low.
- Faulty Mass Air Flow (MAF) signal.

Signal absent:
- Break in signal lead.
- Break in power lead.
- Break in ground lead.
- Contact resistance in connections.
- Defective heated oxygen sensor.

Fault symptom(s)
- High fuel consumption.

TEST PROCEDURE

NOTE: Releasing spray or oil must not be used in HO2S connector.




STATUS REPORT
^ Signal too high:
- Proceed to SIGNAL TOO HIGH section below.

^ Signal too low:
- Proceed to SIGNAL TOO LOW section below.

^ Signal absent:
- Proceed to SIGNAL ABSENT section below.




SIGNAL TOO HIGH
Check signal lead
- Ignition off.
- Disconnect HO2S connector.
- Start engine.
- Enter DTC parameter list.
- Read off HO2S voltage.

Value should be approx. 0.460 volts.

If value OK:
^ Test with new HO2S.

If value differs:
^ Check lead between ECM # 28 and HO2S for short circuit to live.

- After fixing: Check HO2S. Proceed to CHECK HO2S section below.




CHECK HO2S
HO2S can break down as a sequential fault if signal lead has been short-circuited to live. Check HO2S as follows.

- HO2S connected.
- Start engine.
- Enter DTC parameter list.
- Read off HO2S voltage.

Value should alternate between 0.100 - 0.900 volts.

If value differs:
^ Test with new HO2S.




SIGNAL TOO LOW
Check signal lead
- Ignition off.
- Disconnect HO2S connector.
- Start engine.
- Enter DTC parameter list.
- Read off HO2S voltage.

Value should be approx. 0.460 volts.

If value OK:
^ Check air leakage in intake system. Proceed to CHECK AIR LEAKAGE IN INTAKE SYSTEM section below.

If value differs:
^ Check lead between ECM # 28 and HO2S for short circuit to ground.

CHECK AIR LEAKAGE IN INTAKE SYSTEM
- Check for air leakage.
- Check air leakage in intake system.

If no air leakage detected:
^ Check load signal. Proceed to CHECK LOAD SIGNAL section below.

If air leakage detected:
^ Fix as necessary.




CHECK LOAD SIGNAL
- Start engine.
- Gear selector: neutral, A/C: off, warm engine.
- Power consumers such as engine coolant fan, heated rear window, etc.: off.
- Enter DTC parameter list
- Read off load signal.

Value should be 2.3 - 2.4 volts at idle.

If value OK:
^ Test with new HO2S.

If value differs:
^ Check MAF sensor connector for contact resistance and oxidation.

- After fixing, recheck MAF sensor signal.

If value differs:
^ Test with new MAF sensor.




SIGNAL ABSENT
Check signal lead
- Ignition off.
- Disconnect HO2S connector.
- Ignition on.
- Connect a voltmeter between HO2S connection 4 (to ECM) and ground.

Voltmeter should read approx. 0.5 volts.

If value OK:
^ Check HO2S voltage measurement. Proceed to CHECK HO2S VOLTAGE MEASUREMENT section below.

If value differs:
^ Check connector. Proceed to CHECK CONNECTOR section below.




CHECK CONNECTOR
- Ignition off.
- HO2S connector disconnected.
- Check ECM connector and 55-pin connector in central relay unit (A3/F) connection 2 for contact resistance and oxidation.
- ECM connected.
- Ignition on.



- Connect a voltmeter between HO2S connection 4 (to ECM) and ground.

Voltmeter should read approx. 0.5 volts.

If value OK:
^ Source of DTC is bad contact in connector.

If value differs:
^ Check lead between ECM # 28 and HO2S for break.

CHECK HO2S VOLTAGE MEASUREMENT
- Ignition off.
- HO2S connector disconnected.
- Start engine.



- Connect a voltmeter between HO2S connection 1 and ground.

Voltmeter should read battery voltage.

If value OK:
^ Check control point. Proceed to CHECK CONTROL POINT section below.

If value differs:
^ Check connector. Proceed to CHECK CONNECTOR section below.




CHECK CONNECTOR
- Ignition off.
- Check 53-pin connector in central relay unit (A3/E) connection 1 for contact resistance and oxidation.
- HO2S connector disconnected.
- Start engine.



- Connect a voltmeter between HO2S connection 1 and ground.

Voltmeter should read battery voltage.

If value OK:
^ Source of DTC is bad contact in connector.

If value differs:
^ Check lead between HO2S connection 1 and ignition relay (2/46) connection 5 for break.




CHECK FUSE
- Check that fuse 30 is OK.

If fuse OK:
^ Check lead between HO2S 2-pin connection 1 and fuse 30 for break.

If fuse not OK:
^ Check lead between:
- fuse 30 and HO2S
- fuse 30 and fuel priming pump (6/33-2) for short circuit to ground.

CHECK CONTROL POINT
- HO2S connector disconnected.
- Engine running.



- Connect a voltmeter between HO2S connection 1 and 2.

Voltmeter should read battery voltage.

If value OK:
^ Check control point voltage drop. Proceed to CHECK CONTROL POINT VOLTAGE DROP section below.

If value differs:
^ Check lead between HO2S connection 2 and control point (31/57) for break.

CHECK CONTROL POINT VOLTAGE DROP
- HO2S connector disconnected.
- Engine running.



- Connect a voltmeter between HO2S connection 2 and ground.

Voltmeter should read approx. 0 volts.

If value OK:
^ Check signal ground. Proceed to CHECK SIGNAL GROUND section below.

If value differs:
^ Check lead to control point for contact resistance and oxidation.

CHECK SIGNAL GROUND
- Ignition off.
- HO2S connector disconnected.



- Connect an ohmmeter between HO2S connection 3 (to ECM) and ground.

Ohmmeter should read approx. 0 ohms.

If value OK:
^ Test with new HO2S.

If value differs:
^ Check lead between HO2S connection 3 and ECM # 19 for break.