P0506

Diagnostic Chart:

The ECM can control idle speed by electrically controlling the throttle plate, advancing/retarding spark timing or increasing/decreasing the air/fuel ratio. The ability for the ECM to control the throttle plate is performed by the use of the throttle actuator control (TAC) module. This assembly (internal to the: throttle body assembly) houses a DC motor along with two independent throttle position sensors, which relay the position of the throttle plate. The throttle plate is held open 7% by the use of spring pressure for minimum idle air. The throttle plate is also held closed by spring pressure, which keeps the throttle in the idle position in the event of a motor circuit malfunction. The ECM monitors the throttle actuator control system for faults in the TP sensors, TAC motor circuit and for a correlation between the actual and desired throttle plate position. The ECM also compares its commanded idle speed to the actual idle speed to ensure idle control is in check. DTC P0506 will set if the actual idle speed is less than a calibrated amount from the ECM commanded idle speed after a certain period of time.

DTC PARAMETERS
DTC P0506 will set if the actual idle speed is less than 100 rpm from the ECM commanded idle speed when:
^ Condition exists for longer than 2 seconds after the ECM has attempted to correct the condition within a limited range
^ ECT is greater than 80°C (176°F)
^ IAT is greater than 0°C (32°F)
^ Vehicle speed = 0 mph
^ EVAP diagnostics are not running
^ No ECT, EVAP leak, EVAP purge solenoid, IAT, TP or vehicle speed DTCs have been set

DTC P0506 diagnostic runs continuously once the above conditions have been met.

P0506 is a type B DTC.

DIAGNOSTIC AIDS

IMPORTANT: If a fuel trim, HO2S, MAF, misfire, system voltage, throttle actuator or TP sensor DTC is also set, diagnose that DTC first.

Verify the ECM ability to control engine speed by using the Scan tool to perform the ENGINE SPEED CONTROL special function. The test will allow the RPM to be raised or lowered in increments of 25, 100 and 500 rpm. Compare the actual ENGINE SPEED to the DESIRED IDLE SPEED. Both should be within 100 rpm of each other.

Make an underhood visual inspection first. Possible causes of low idle speed:
^ Air induction tubing cracked, damaged or loose
^ Carbon around throttle plate/bore
^ Accessory drive component loading engine
^ System voltage low