What does it mean?
P1504 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Idle Air Control Valve Circuit Continuity-Open Load .
Symptoms
- Check engine light on with idle data stored in freeze frame
- Idle held at a fixed base value, usually too low
- Engine stalls when coming to a stop or when the clutch is pressed
- No idle-up when the A/C compressor, headlights or blower switch on
- Hard cold starting, or the throttle has to be held slightly open to keep the engine running
- Idle stays uneven long after the engine has warmed up
Likely causes
- Open winding inside the idle air control valve motor
- Corroded, spread or backed-out terminals in the valve connector
- Broken or chafed wire between the module and the valve, typically where the harness flexes near the intake
- Missing ignition-switched feed to the valve because of a blown fuse or a failed relay contact
- Poor module ground or a failed low-side driver inside the module
- Non-original valve whose coil resistance falls outside the range the module expects
How to fix it
- Read freeze frame and note whether the fault is current or historic, then clear it and run the engine at idle again
- Inspect the valve connector for corrosion, oil contamination and spread terminals, then reseat and clean it
- Measure the valve winding resistance at the component; an infinite reading confirms the open coil
- With the ignition on, check for battery voltage on the supply pin and continuity on the drive wire back to the module connector
- Wiggle-test the harness while watching resistance to catch an intermittent open
- Replace the idle air control valve if the winding is open, using an original-specification part
- Only after wiring and valve test good, check the module driver output and consider module repair