Trouble Code Conditions

2-1-2 FRONT HEATED OXYGEN SENSOR, SIGNAL





Trouble Code Conditions
- Before fuel trim starts the front heated oxygen sensor (HO2S) must be ready - it should be at operational temperature and have the correct output voltage. Monitoring of the heated oxygen sensor function starts approx. 3 minutes after heated oxygen sensor heating starts. Diagnostic trouble code (DTC) EFI-212 is stored if there is a fault in the front or rear heated oxygen sensors or their cabling that affects the output voltage from the front heated oxygen sensor.

Substitute value(s)
- Fuel trim disabled.
- Three-way catalytic converter (TWC) diagnostic disabled.

Possible source(s)
Signal too high:
- Short-circuit to supply voltage in front heated oxygen sensor signal cable (+).
- Short-circuit to supply voltage in front heated oxygen sensor signal cable (-).
- Short-circuit to supply voltage in rear heated oxygen sensor signal cable (+).
- Short-circuit to supply voltage in rear heated oxygen sensor signal cable (-).
- Defective front heated oxygen sensor.
- Defective rear heated oxygen sensor.

Signal too low:
- Short-circuit to ground in front heated oxygen sensor signal cable (+).
- Short-circuit to ground in front heated oxygen sensor signal cable (-).
- Short-circuit to ground in rear heated oxygen sensor signal cable (+).
- Short-circuit to ground in rear heated oxygen sensor signal cable (-).
- Defective front heated oxygen sensor.
- Defective rear heated oxygen sensor.

Signal missing:
- Open-circuit in signal cable.
- Open-circuit in signal cable.
- Defective front heated oxygen sensor.

Faulty signal:
- Signal cable (+) short circuited to signal cable.
- Defective front heated oxygen sensor.

Fault symptom(s)
- None.





Other Diagnostic Trouble Codes
- Read off other diagnostic trouble codes.
- Is diagnostic trouble code EFI-521 stored?

Yes:
^ See: Code EFI-521, Front Heated Oxygen Sensor, Heating and Code EFI-522 Rear Heated Oxygen Sensor, Heating.

No:
^ Proceed to test step below.





Other DTCs and Status Messages
Status message
- Select one of the following options to continue:

Alternative 1:
- Refer to: Signal Too High. Permanent Fault.

Alternative 2:
- Refer to: Signal Too Low. Permanent Fault.

Alternative 3:
- Refer to: Signal Missing. Permanent Fault.

Alternative 4:
- Refer to: Faulty Signal. Permanent Fault.

Alternative 5:
- Refer to: Signal Too High. Intermittent Fault.

Alternative 6:
- Refer to: Signal Too Low. Intermittent Fault.

Alternative 7:
- Refer to: Signal Missing. Intermittent Fault.

Alternative 8:
- Refer to: Faulty Signal. Intermittent Fault.