P0491

Test 1 - 4:

Test 5 - 8:

Test 9 - 11:

SYMPTOM
P0491-AIR INJECTION SYSTEM PERFORMANCE

WHEN MONITORED
Engine Running. The Air Injection Pump is active for a calibrated amount of time. Once enough air flow has accumulated through the Air Injection system the test will begin.

SET CONDITION
If the PCM detects excessive air flow or not enough air flow though the Air Injection system a fault is recorded. Two Trip Fault.

POSSIBLE CAUSES
- Good trip equal to zero
- Visual and physical inspection of the air injection system
- ASD relay output circuit
- MAF sensor internal failure
- MAF signal circuit shorted to ASD relay output circuit
- MAF signal circuit shorted to battery voltage
- MAF signal circuit open
- MAF signal circuit shorted to ground
- MAF signal circuit shorted to (K4) sensor ground circuit
- Sensor ground circuit open
- PCM