Electronically Controlled Transmission (ECT) Circuit
- Start engine and bring to operating temperature. Drive vehicle and ensure overdrive operation is turned on and off when overdrive ON-OFF switch is operated. If overdrive switch is okay, go to next step. If overdrive switch is not okay, see appropriate ELECTRONIC CONTROLS article in AUTOMATIC TRANSMISSIONS.
- Turn ignition switch to OFF position. Remove cruise control ECU and disconnect connector. See Figure. Turn ignition switch to ON position. Measure voltage by backprobing between cruise control ECU harness connector terminal No. 14 (Red/White wire) and ground. If battery voltage is present, go to next step. If battery voltage is not present, go to step 5.
- Turn ignition switch to OFF position. Reconnect cruise control ECU connector. Bring engine to operating temperature and test drive vehicle with overdrive switch moved from ON to OFF position. Measure voltage by backprobing between cruise control ECU connector terminal No. 6 (Brown/Yellow wire) and ground. With overdrive in OFF position, voltage should be less than .5 volt. With overdrive in ON position, battery voltage should be present. If voltage is not as specified, go to next step. If voltage is as specified, no problem is indicated at this time. Fault may be intermittent. If sent here from SYMPTOM TESTS, perform next test under appropriate symptom.
- Check wiring harness and connectors between cruise control ECU terminal No. 6 (Brown/Yellow wire) and electronically controlled transmission solenoid. Repair as necessary. If wiring harness and connectors are okay, replace cruise control ECU and retest system.
- Check wiring harness and connectors between cruise control ECU connector terminal No. 14 (Red/White wire) and Engine Control Module (ECM) 16-pin connector terminal No. 9 (Red/White wire). Repair as necessary. If wiring harness and connectors are okay, replace cruise control ECU and retest system.