Diagnostic Aids

Check for any of the following conditions:

• High electrical load parameter on scan tool can indicate if PCM has received rear defogger or parking lamps on signal. Scan tool should indicate YES when rear defogger or parking lamps are turned on and engine speed should increase slightly. Check for fault in IAC system or short to ground in diagnostic request circuit if engine speed does not increase.
• Malfunctioning taillight circuit may cause erratic performance of electrical load idle-up circuit.
• Shorted PSP switch can cause engine idle speed to remain high even when driving straight ahead.
• Incorrectly calibrated PSP switch can cause engine idle speed to remain low when steering pump hydraulic pressure is high.
• Faulty ground for PSP switch can cause erratic switch operation. Ensure power steering pump and bracket are secure, insuring a good ground path. Check PSP switch for tight installation.
• Scan tool will display A/C relay command on when air conditioning control is turned on, blower switch is on, and A/C compressor is operating.
• Observe IAC duty cycle on scan tool while operating A/C. IAC duty cycle should increase 4 to 12 percent when A/C compressor is engaged. If scan tool indicates IAC duty cycle is increasing, but idle quality is unsatisfactory, inspect IAC system for proper operation.
• Check for a poor connection, rubbed-through wire insulation, or a wire broken inside insulation. Inspect PCM harness connector for backed-out terminals, improper mating, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.