DTC EFI-521

5-2-1 FRONT HEATED OXYGEN SENSOR PREHEATING





Trouble Code Conditions
- Monitoring of the heated oxygen sensor (HO2S) heating circuit starts approx. 3 minutes after heated oxygen sensor heating starts. Diagnostic trouble code (DTC) EFI-521 or EFI-522 are stored it the engine control module (ECM) registers too high or low a current in the heating circuit.

Substitute value(s)
- Twin heated oxygen sensor control disabled.

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

Signal too low:
- Short-circuit to ground in signal cable.
- Open-circuit in signal or power cable.
- Contact resistance in terminals.
- Detective heated oxygen sensor.

Fault symptom(s)
- None.