P0491

P0491

Secondary Air Injection System, Bank 1 - Below Limit

Diagnostic conditions
- Intake air temperature between 4.5 °C and 80 °C
- Engine starting temperature below 37 °C
- Engine temperature above 4.5 °C
- Air mass between 16 kg/h and 160 kg/h
- Oxygen sensor ahead of TWC operational
- Oxygen sensor basic adaption completed
- No fault in secondary air injection pump output stage
- Diagnosis has not yet taken place during this cycle

Possible cause of fault
- Fuse F3 faulty
- Open circuit to secondary air injection pump
- Short circuit to ground in the lead to secondary air injection pump
- Secondary air injection pump relay mechanically faulty
- Secondary air valve sluggish
- Secondary air injection pump (air cleaner) blocked
- Air hose to secondary air injection pump slipped off or crushed
- Secondary air injection pump faulty/stuck

Affected terminals
Secondary air injection pump relay, bank 1, pin 2 and secondary air injection pump, bank 1, pin 2

Diagnosis/troubleshooting

NOTE:
- The fault is set if 75 % of the conveyed secondary air mass when driving or 50 % of the conveyed air mass during the short test is lacking.
- This is diagnosed via the oxygen sensors.

NOTE: The lead from the secondary air injection pump relay, bank 1, pin 2, to the secondary air injection pump, bank 1, pin 2, is routed via the KE 1 disconnection point, pin 3.