P1551

DTC P1551
Idle Air Control Valve fault (closing) Drive cycle A:Signal missing.

Possible causes by suggested order of priority:
- Short circuit C641/1 (RG) to vehicle +12V.
- Short circuit C641/1 (RG) to vehicle earth.
- Open circuit C641/1 (RG) to C636/43 (RG).
- Connector(s) C641,ECM C636 (B).
- Voltage incorrect C641/2 (NK) to vehicle earth.
- Faulty IACV (closing coil).
- Faulty ECM.

Short circuit C641/1 (RG) to vehicle +12V.
- Check resistance < 5.0 Ohm

Short circuit C641/1 (RG) to vehicle earth.
- Check resistance > 1M Ohm

Open circuit C641/1 (RG) to C636/43 (RG).
- Check resistance > 1M Ohm

Connector(s) C641,ECM C636 (B).
- Check for connector not correctly latched, backed out pins, damaged pins, corroded pins

Voltage incorrect C641/2 (NK) to vehicle earth.
CHECK THE FOLLOWING:
- Voltage incorrect C641/2 (NK) to vehicle earth..
ACCEPTABLE RESULTS
Between 11.5V and 15.0V.
DIAGNOSTIC HINTS
- If the voltage is not present check F2 Engine Compartment Fusebox and open circuit C641/2 (NK) to C570/1 (NK).

Faulty IACV (closing coil).
CHECK THE FOLLOWING:
- Disconnect C641. Use a multimeter to check the resistance of the IACV closing coil (C641/2 (NK) to C641/1 (RG)). Acceptable range 10 Ohms to 100 Ohms.
- Check IACV by substituting a known good unit.
POSSIBLE FAULTS
- IACV Faulty

Faulty ECM.
CHECK THE FOLLOWING:
- Eliminate all other fault possibilities before suspecting the ECM.
- Failure of this component is unlikely.
- Check ECM by substituting a known good unit.
POSSIBLE FAULTS
- ECM Faulty