Test 3 (Elect Controlled Trans Communication CKT)

To reduce frequent automatic shifting between Drive and Overdrive when speed is set, the cruise control ECU communicates with the engine/transmission ECM as follows:

• When transmission has downshifted from Overdrive to Drive as a result of vehicle driving uphill, cruise control ECU detects downshift through terminal ECT.
• At terminal OD, cruise control ECU grounds reference signal received from engine/transmission ECM (terminal OD1).
• When engine/transmission ECM detects that reference signal has been grounded, it keeps transmission in Drive until end of uphill climb.

1. Warm engine to operating temperature. Drive vehicle to ensure overdrive operates. If overdrive does not operate, repair transmission. If overdrive operates, remove cruise control ECU. Disconnect electrical connector from cruise control ECU.
2. Turn ignition on. At cruise control ECU connector, measure voltage between ground and terminal no. 9. See Figure.
3. Voltage should be 4-6 volts. If voltage is as specified, go to next step. If voltage is not as specified, check for faulty circuit between cruise control ECU and engine/transmission ECM. If circuit is okay, replace engine/transmission ECM.
4. Turn ignition off. Reconnect electrical connector to cruise control ECU. Warm engine to operating temperature. Connect voltmeter between ground and terminal no. 22 of cruise control ECU connector. See Figure.
5. While driving vehicle, have an assistant watch voltmeter. With transmission in Drive, battery voltage should be present. With transmission in Overdrive, less than one volt should be present.
6. If voltage is as specified, perform next procedure listed in DIAGNOSIS BY SYMPTOM table. If voltage is not as specified, check for faulty circuit between cruise control ECU and shift solenoid No. 2. If circuit is okay, replace cruise control ECU.