Diagnostic Aids

Check for any of the following conditions:

• The "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 a malfunction in IAC system or a short to ground in Diagnostic Request circuit if engine speed does not increase.
• A malfunctioning parking lamp (taillight) circuit may cause erratic performance of electrical load idle-up circuit.
• A PSP switch that is shorted can cause engine idle speed to remain high even when driving straight ahead.
• A PSP switch that is incorrectly calibrated can cause engine idle speed to remain low when steering pump hydraulic pressure is high.
• A faulty ground in PSP switch can cause erratic switch operation. Ensure power steering pump and bracket are secure, insuring a good path to ground. Inspect PSP switch for a tight installation.
• Scan tool will display "A/C Relay Command On" when air conditioning control is turned ON, blower switch is also ON, and A/C compressor is operating.
• Observe IAC Motor Command on scan tool while operating A/C. IAC Motor Command percentage should increase 4-12 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.
• If scan tool indicates IAC Motor Command is increasing, but idle quality is unsatisfactory, inspect IAC system for proper operation. See IDLE AIR CONTROL SYSTEM DIAGNOSIS (2.0L)  or IDLE AIR CONTROL SYSTEM DIAGNOSIS (2.5L)  .
• An intermittent malfunction may be caused by a fault in any one of the idle-up circuits. Inspect wiring harness and components for an intermittent condition. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - TRUCKS article.