Table C-1B A/C Idle-Up Circuit Check

Table C-2A A/C Idle-Up Circuit Check:

Idle-Up Circuit:

Circuit Description
This signal is sent from the A/C amplifier. The Engine Control Module (ECM) detects whether or not the A/C system is operating via the A/C amplifier. The extra load the A/C system demands from the engine requires a higher idle speed. When the ECM receives the A/C "ON" signal, it will activate the Idle Air Control (IAC) valve and the idle speed will increase.

Diagnostic Aids
An intermittent malfunction may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connections before component replacement.

Using a scan tool you can monitor the A/C switch parameter. When the A/C switch is in the "ON" position and the blower speed is in any speed except "OFF," the scan tool should read "ON," and when the A/C switch is "OFF" the scan tool should read "OFF."

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
2. This checks for an open or short to ground in YEL/BLK wire, or a faulty ECM.
3. This checks for a faulty ECM or for a faulty A/C amplifier.