P0506

Diagnostic Chart:

Schematic:

The idle speed on DOHC and SOHC engines is controlled by the PCM via an Idle Air Control (IAC) valve. The IAC valve consists of a two coil stepper motor that moves a pintle valve in and out from the seat controlling the amount of air entering the intake manifold. The PCM controls the IAC valve by supplying ignition voltage or ground to any of the four circuits of coil "A" or coil "B". When one circuit of a coil is supplied ignition voltage, the other side is supplied ground. Coil "A" and coil "B" are independent of each other, however both must be functional in order for the valve to move. The IAC position is measured in counts which can be read on the Scan tool. When the engine is turned Off, the IAC is retracted 80 to 100 counts allowing for maximum air during a restart. After the engine is started, the motor position command is based on ECT and TP sensor values. DTC P0506 sets when the actual engine speed is 100 RPM or more below the desired engine speed.

DTC PARAMETERS
DTC P0506 will set if idle speed is too low when:
^ Actual engine speed is 100 RPM or more below the desired idle speed
^ STFT is between 122 and 134 counts
^ ECT is greater than 60°C (140°F)

DTC P0506 diagnostic runs continuously every 17 seconds when the above conditions have been met. DTC P506 is a type B DTC.

DIAGNOSTIC AIDS

IMPORTANT: If DTC P0508 or P0509 is set, diagnose that DTC first. A diagnosed IAC valve circuit may have caused this DTC to set.

To locate an intermittent problem, use Scan tool to command different idle speed Rpms (650-875). ENGINE SPEED should match the DESIRED IDLE SPEED within 100 RPM.

IAC terminal resistance:
^ A to B 40-80 ohms
^ C to D 40-80 ohms
^ All other combinations should be open

Use flowchart for possible causes of low idle speed.