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Electronically Controlled Transmission Communication Circuit

  1. Warm engine to operating temperature. Drive vehicle to ensure overdrive operates. If overdrive does not operate, repair transmission before continuing test. If overdrive operates, go to next step.
  2. Remove cruise control ECU, leaving electrical connector attached. Turn ignition on. Disconnect electrical connector from cruise control ECU. Measure voltage (backprobe) between cruise control ECU connector terminal No. 14 and ground. See Figure. Voltage should be 10-14 volts. If voltage is as specified, go to next step. If voltage is not as specified, go to step  5.
  3. Connect cruise control ECU connector. Warm engine to operating temperature. Test drive vehicle and have an assistant measure voltage (backprobe) between cruise control ECU connector terminal No. 6 and ground while operating overdrive switch. See Figure. With overdrive switch on, voltage should be 8-14 volts. With overdrive switch off, voltage should be less than 0.5 volt. If voltage is not as specified, go to next step. If voltage is as specified, perform next procedure listed in SYMPTOM DIAGNOSIS  table under TROUBLE SHOOTING.
  4. Check wiring and connectors between cruise control ECU and electronically controlled transmission solenoid. Repair or replace as necessary. If wiring and connectors are okay, check cruise control ECU. See CRUISE CONTROL ECU PIN VOLTAGE TESTS  under COMPONENT TESTS. If cruise control ECU is defective, replace ECU.
  5. Check wiring and connectors between cruise control ECU and Engine Control Module (ECM). Repair or replace as necessary. If wiring and connectors are okay, check cruise control ECU. See CRUISE CONTROL ECU PIN VOLTAGE TESTS  under COMPONENT TESTS. If cruise control ECU is defective, replace ECU.
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