Diagnostic Trouble Code (DTC) Information

Diagnostic trouble code (DTC) information EFI-521, EFI-522

EFI-521 Front heated oxygen sensor (HO2S), preheating EFI-522 Rear heated oxygen sensor (HO2S), preheating

Condition




Monitoring of the heated oxygen sensor (HO2S) heating circuit begins approximately 3 minutes after the HO2S heating sequence starts. Diagnostic trouble codes (DTCs) EFI-521 or EFI-522 are stored if the engine control module (ECM) registers too high or low a current in the heating circuit.

Substitute value
- 2-heated oxygen sensor (HO2S) control disabled

Possible source

Signal too high:
- short-circuit to supply voltage in signal cable
- defective heated oxygen sensor (HO2S).

Signal too low:
- short-circuit to ground in signal cable
- defective fuse 11B/5 (1998-)
- open-circuit in signal- or power cable
- contact resistance in terminals
- defective heated oxygen sensor (HO2S).

Fault symptom[s]
- none.