Engine

P1504 — Idle Air Control Valve Control Circuit High

Severity: low Drive with care, to a shop

What P1504 means

P1504 is a manufacturer-specific code, so its definition varies by brand. In its generic form, the engine control module sees an open circuit or abnormally high voltage in the idle air control (IAC) valve control circuit. The IAC valve lets a metered amount of air bypass the closed throttle plate to keep idle speed steady.

Symptoms

  • High idle speed
  • Surging or hunting idle
  • Stalling when stopping or braking
  • Hard or unstable starting
  • Check Engine light on

Possible causes

  1. Open or poor connection in the IAC control wiring
  2. Failed IAC valve (coil or stepper motor)
  3. Disconnected or corroded IAC connector
  4. Dirty or sticking valve or air passage
  5. Faulty engine control module (rare)

How to diagnose

  1. Scan all codes and freeze-frame data, clear the code and see whether it returns.
  2. Inspect the IAC valve connector and harness for looseness, corrosion and damaged insulation.
  3. Watch idle speed and its response to loads such as lights and A/C with a scan tool.
  4. Measure the IAC valve coil resistance and compare it with the spec for your vehicle.
  5. Check for power and ground at the connector with the ignition on.
  6. Test the control wire from the valve to the ECM for opens and shorts.
  7. Remove the valve and throttle body and look for carbon buildup or sticking.
  8. If wiring and valve are good, test the ECM.

Common fixes

  • Repair the wiring or replace a damaged connector
  • Replace the idle air control valve
  • Clean the throttle body and IAC passage, then perform an idle relearn
  • Replace or reprogram the ECM if it is confirmed faulty

P1504 on different brands

Chrysler
Vehicle Speed Output circuit: the module found improper operation in that circuit.
Ford · manuals
Intake Air Control circuit malfunction.
Hyundai · manuals
Cruise Control Malfunction - Cancel.
Kia · manuals
Cruise control master switch signal malfunction.
Land Rover
Idle air control (IAC) fault.
Mazda · manuals
Idle air control (IAC) system circuit malfunction.
MINI
Open circuit in the idle speed control valve closing solenoid control.
Subaru · manuals
Vehicle speed sensor CAN malfunction.

Questions and answers

What does P1504 mean?

It is a manufacturer-specific code. On many engines it points to an open or high condition in the idle air control valve circuit, but on Chrysler, Ford, Hyundai, Kia and Subaru it means something different. Check the definition for your brand.

Can I drive with P1504?

If it relates to the idle air control valve, you can usually drive carefully for a short time, but the engine may stall at stops. Do not put off diagnosis.

How do I fix P1504?

Start with the valve connector and wiring, then test the valve and clean the throttle body. Most often the fix is a wiring repair or a new IAC valve.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.