What does it mean?
P1503 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Idle Air Control Valve Circuit Short to Ground .
Symptoms
- MIL on
- Idle speed too high, too low, or constantly hunting up and down
- Stalling when coming to a stop or when the A/C compressor engages
- Hard starting, needing throttle to keep the engine running
- No idle-up when headlights or other electrical loads are switched on
- Erratic idle immediately after a cold start
Likely causes
- Idle air control valve control circuit shorted to ground
- Valve motor winding shorted internally
- Harness chafed and grounding against the intake manifold or a bracket
- Connector corroded or contaminated with oil from a crankcase ventilation leak
- Valve pintle seized with carbon, forcing high current draw that damages the circuit
- Poor ground or wiring damaged during previous intake work
- Module output driver stuck low
How to fix it
- Compare the commanded valve position on the scan tool with actual idle speed
- Unplug the valve and note whether idle behaviour changes at all
- Measure the resistance of each winding and compare it with specification
- With the valve disconnected, check the control wires for a short to ground
- Remove the valve and clean the pintle and its passage of carbon deposits
- Check for vacuum leaks that force the valve to sit at an extreme position
- Repair the wiring or replace the valve, then carry out the idle relearn procedure if one is specified