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Home >> Chevrolet >> 2000 >> Prizm Base, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System & Component Testing >> Circuit Tests >> Electrical Load Idle-Up Circuit (1.8L) >> Diagnostic Procedure

Diagnostic Procedure

NOTE: Before proceeding with this test, ensure rear defogger and parking lights 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. Monitor Idle Air Control valve (IAC) duty cycle while turning rear window defogger on and off. Duty cycle should increase between 3-5 percent and engine RPM should increase as well. If engine RPM or duty cycle of IAC does not increase when defogger switch is turned on, go to step  4. If engine RPM or duty cycle of IAC does increase, go to next step.
  3. Monitor IAC duty cycle and engine RPM while turning parking lights on and off. If engine RPM does not increase when switch is turned on, go to step  6. If engine RPM does increase, system is functioning normally.
  4. Turn ignition on, engine off. Using a test light connected to ground, backprobe electrical load idle-up signal circuit at PCM connector C3, terminal No. 2 (M/T and 3-speed A/T) or connector C3, terminal No. 10 (4-speed A/T). Turn rear defogger switch to ON position. If test light illuminates, go to step  8. If test light does not illuminate, go to next step.
  5. Turn ignition off. Disconnect PCM connector C3. Check for an open or short in electrical load idle-up signal circuit between rear defogger switch and PCM. Repair as necessary. After repairs, go to step  10. If circuit is okay, go to step  9.
  6. Turn ignition on, engine off. Using a test light connected to ground, backprobe electrical load idle-up signal circuit at PCM connector C3, terminal No. 3 (M/T and 3-speed A/T) or connector C3, terminal No. 20 (4-speed A/T). Turn parking light switch on. If test light illuminates, go to step  8. If test light does not illuminate, go to next step.
  7. Turn ignition off. Disconnect PCM connector C3. Check for an open or short in electrical load idle-up signal circuit between parking light switch and PCM. Repair as necessary. After repairs, go to step  10. If circuit is okay, go to next step.
  8. Check for a short to ground in diagnostic request circuit between underhood data link connector and PCM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. After repairs, go to step  10. If circuit is okay, go to next step.
  9. Replace PCM. After repairs, go to next step.
  10. After repairs are completed, operate vehicle within conditions under which original symptom was observed. If system operates properly, repair is complete. If system does not operate properly, see DIAGNOSTIC AIDS .
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