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Home >> Chevrolet >> 2001 >> Prizm Base, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System & Component Testing >> Circuit Tests >> Electrical Load Idle-Up Circuit (Metro) >> Diagnostic Procedure

Diagnostic Procedure

NOTE: Before proceeding with this test, ensure rear defogger, parking lights and blower motor all operate properly.
  1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. After performing OBD system check, go to next step.
  2. Install scan tool. Start and warm engine to normal operating temperature. Turn off all accessories. Using scan tool, monitor electrical load parameter while turning parking lights, rear window defogger, and blower motor on and off. If scan tool does not indicate ON when accessories are turned on and off, go to next step. If scan tool indicates ON and OFF, system is functioning normally.
  3. If engine RPM does not increase when at least one accessory is turned on, go to next step. If engine RPM does increase, go to step  7.
  4. Turn ignition off. Disconnect PCM connectors. Turn ignition on, engine off. Using a test light connected to ground, probe PCM connector electrical load idle-up signal circuit. See WIRING DIAGRAMS article. Turn headlight switch to PARK or HEAD position. If test light illuminates, go to next step. If test light does not illuminate, go to step  6.
  5. Check for poor terminal connections at PCM. Repair as necessary. After repairs, go to step  10. If connections are okay, go to step  9.
  6. Check for an open in electrical load idle-up signal circuit between diode module and PCM. Repair as necessary. After repairs, go to step  10. If circuit is okay, go to step  8.
  7. Check components and circuits in related systems which did not increase engine RPM:
    • Faulty blower motor speed selector switch, poor connection or an open in blower motor speed selector switch circuit to diode module.
    • Faulty headlight switch, poor connection or an open in headlight switch circuit to diode module.
    • Faulty rear defogger switch, poor connection or an open in rear defogger switch circuit to diode module. Repair as necessary. After repairs, go to step  10. If no repairs were necessary, go to next step.
  8. Replace diode module. After repairs, go to step  10.
  9. Replace PCM. After repairs, go to next step.
  10. After repairs, operate vehicle within conditions under which original symptom was observed. If system operates properly, repair is complete. If system does not operate properly, go to DIAGNOSTIC AIDS .
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