DTC Decoded: P1504

Ford DTC Code: P1504

Code Meaning: Intake Air Control Circuit Malfunction

Symptoms:

  • Service Engine Soon Light illuminates
  • Rough idle
  • Pulsing idle
  • Hard cold start

Causes:

  • Idle Air Control Valve harness is damaged
  • Idle Air Control Valve circuit has a bad electrical connection
  • Idle Air Control Valve is faulty

IAC valve

Description

When you see this code, there has been a detection by the Powertrain Control Module (PCM) of an electrical load failure of the Idle Air Control (IAC) circuit. This means that there may be an open or a short in the harness, the connection may be damaged, or the IAC is dirty or faulty.

Your IAC valve is in control of the engine idle speeds and lets the air bypass the engine’s throttle plate. It is only in fuel-injected vehicles, and it is controlled by information it receives from the ECM or PCM. If the valve is not operating properly, it can send too much air in. The PCM then will detect more air than it expects and trigger a check engine light. The PCM gets its data from a variety of sensors and then it sends out adjustment signals that affect the amount of air received by the engine. The IAC is not used at any speeds over an idle, which is why you will notice a fault in it at start up or waiting in traffic. You may notice it before the check engine light is illuminated.

The IAC has air ports that are sealed with gaskets that may begin leaking, which can cause the IAC to lose performance.

If the IAC is dirty from a build up of carbon, it will not operate properly, which can result in a high idle speed, rough idle or hard cold starting. A dirty IAC may also cause a pulsing idle. The bore air passages should be cleaned out any time you do a tune up.

What the Tech Says

Since the problem can be in a few places, you should first check for obvious signs of damage around the idle control valve and its wiring. If you see no sign of damage, then you will want to take it apart. Check the gasket and replace if necessary. Then clean the air ports to remove any carbon build up. Reassemble and return the IAC to the engine.

If a good cleaning does not fix the problem, you may need to replace the unit. Since the IAC has a lot of air that is pushed through it with a huge amount of pressure, it is possible that the unit is dirty or the gasket is leaking.