Diagnosis & Repair
- Remove glove box for access to ECM with electrical connectors still installed on ECM. See Figure. Waveform pattern should be checked for throttle control motor M+ and M- circuits at ECM. Connect oscilloscope between terminals No. 17 (Brown wire) at ECM electrical connector E10 and No. 9 (Red wire; M+ circuit) or No. 31 (Green wire; M- circuit) at ECM electrical connector E9. This is the E1, M+ and M- terminals on ECM. For ECM electrical connector terminal identification, see Figure. Start engine and allow engine to idle. Note M+ and M- waveform pattern with engine idling. Ensure M+ and M- waveform patterns are properly displayed. See Fig 1. Ensure engine is idling when checking waveform pattern, as waveform pattern will change with throttle opening. If any waveform pattern is not as shown, shut engine off. Go to next step. If both waveform patterns are as shown, shut engine off. Replace ECM.
- Check resistance of throttle control motor by checking resistance between terminals No. 1 and 2 on throttle control motor. See THROTTLE BODY under IDLE CONTROL SYSTEMS in SYSTEM & COMPONENT TESTING - V6 & V8 article. If throttle control motor is okay, go to next step. If throttle control motor is defective, replace throttle body with throttle control motor as an assembly. See THROTTLE BODY under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION - V6 & V8 article.
- Check for open and short in Green and Red wires and electrical connectors between throttle control motor and ECM. See WIRING DIAGRAMS article. If wiring harness and electrical connectors are okay, replace ECM. If wiring harness or electrical connector is defective, repair as necessary.
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