Diagnosis & Repair
WARNING: This page is about a different car, the 2002 Lexus ES 300. However, it is still accessible from the selected car via links, so may be relevant.
- Access ECM behind glove box. Start engine. Using oscilloscope, check signal circuits of M+ and M- circuits between ECM and throttle control motor. Backprobe ECM at following terminals:
- For M+ Circuit
Connect oscilloscope between terminal No. 3 of ECM connector E8 (Black wire) and terminal No. 1 of ECM connector E8 (Brown wire). See Figure. - For M- Circuit
Connect oscilloscope between terminal No. 2 of ECM connector E8 (White wire) and terminal No. 1 of ECM connector E8 (Brown wire). See Figure.
Compare to specified oscilloscope patterns. See Fig 1. Waveform frequency should vary with engine speed. If either circuit does not display specified waveform, go to next step. If both circuits display specified waveform, replace ECM and retest system.
- For M+ Circuit
- Disconnect throttle control motor 2-pin connector. Measure resistance of motor between connector terminals at throttle control motor connector. Resistance should be .3-100.0 ohms at 68°F (20°C). If resistance is not as specified, replace throttle control motor. If resistance is as specified, go to next step.
- Check for open or short circuit in wiring harness or connector between throttle control motor and ECM. See WIRING DIAGRAMS article. Repair wiring as necessary. If wiring and connectors are okay, replace ECM and retest.