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Test No. 3: Actual Vehicle Speed Deviates From Set Speed

WARNING: This page is about a different car, the 2002 Toyota Avalon. However, it is still accessible from the selected car via links, so may be relevant.
  1. Check cruise control actuator control cable adjustment. See CRUISE CONTROL ACTUATOR CONTROL CABLE  under ADJUSTMENTS. If cruise control actuator control cable adjustment is okay, go to next step. If cruise control actuator control cable adjustment is not okay, adjust as required. After repairs, perform confirmation test. See CONFIRMATION TEST .
  2. Check vehicle speed sensor. See DTC 23: VEHICLE SPEED SENSOR SIGNAL ABNORMAL  test under DIAGNOSTIC TESTS. If vehicle speed sensor is okay, go to next step.
  3. Start engine and warm to operating temperature. Test 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 DIAGNOSIS - A-541E article in AUTOMATIC TRANSMISSIONS.
  4. Turn ignition off. Remove cruise control ECU with connector attached. See Figure. Turn ignition on. Disconnect cruise control ECU 16-pin electrical harness connector. Using a DVOM, measure voltage by backprobing between cruise control ECU 16-pin electrical harness connector terminal No. 14 (Gray wire) and good body ground point. See Figure. If voltage is 10-14 volts, go to next step. If voltage is not 10-14 volts, go to step  7.
  5. Turn ignition off. Reconnect cruise control ECU 16-pin electrical harness connector, but do not install cruise control ECU. Start and warm engine to normal operating temperature. Test drive vehicle. During test drive, measure voltage by backprobing between cruise control ECU 16-pin electrical harness connector terminal No. 6 (Green/Yellow wire) and good body ground point when overdrive switch is turned to ON and OFF positions. See Figure. With overdrive switch in OFF position, voltage should be less than .5 volt. With overdrive switch in ON position, voltage should be 8-14 volts. 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, go to step  8.
  6. Turn ignition off. Disconnect cruise control ECU 16-pin electrical harness connector and electronically controlled transmission solenoid 6-pin Gray electrical harness connector. Using a DVOM, check for open and short circuit conditions in Green/Yellow wire between cruise control ECU 16-pin electrical harness connector terminal No. 6 and electronically controlled transmission solenoid 6-pin Gray electrical harness connector terminal No. 6. See Figure. If wires, harnesses and connectors are okay, go to step  10. If wires, harnesses and connectors are not okay, repair fault as required. See TRANSMISSION in SYSTEM WIRING DIAGRAMS article. After repairs, perform confirmation test. See CONFIRMATION TEST .
  7. Turn ignition off. Locate engine control module and disconnect engine control module 28-pin electrical harness connector E7. Also disconnect cruise control ECU 16-pin electrical harness connector. See Figure. Using a DVOM, check for open and short circuit conditions in Gray wire between cruise control ECU 16-pin electrical harness connector terminal No. 14 and engine control module 28-pin electrical harness connector E7 terminal No. 24. See Figure. If wires, harnesses and connectors are okay, go to step  10. If wires, harnesses and connectors are not okay, repair fault as required. See CRUISE CONTROL in SYSTEM WIRING DIAGRAMS article. After repairs, perform confirmation test. See CONFIRMATION TEST .
  8. Check cruise control actuator circuit. See DTC 11: SHORT IN CRUISE CONTROL ACTUATOR CIRCUIT OR DTC 15: OPEN IN CRUISE CONTROL ACTUATOR CIRCUIT  test under DIAGNOSTIC TESTS. If cruise control actuator circuit is okay, go to next step.
  9. Check idle signal circuit. See DTC 51: IDLE SIGNAL CIRCUIT  test under DIAGNOSTIC TESTS. If idle signal circuit is okay, go to next step.
  10. Turn ignition off. Disconnect cruise control ECU 16-pin electrical harness connector. Using DVOM, check cruise control ECU ground circuit. See CRUISE CONTROL in SYSTEM WIRING DIAGRAMS article. If ground circuit is faulty, repair and retest system. If ground circuit is okay, substitute original cruise control ECU with a known-good unit and recheck system operation. If system operates properly, original cruise control ECU was defective. If system still does not operate properly, perform cruise control ECU pin voltage check. See PIN VOLTAGE TESTS . Check wiring harness and electrical connectors for an intermittent problem. Repair wiring harnesses or connectors as necessary. See CRUISE CONTROL in SYSTEM WIRING DIAGRAMS article. If voltage values, harnesses and connectors are okay, replace cruise control ECU. See CRUISE CONTROL ELECTRONIC CONTROL UNIT  under REMOVAL & INSTALLATION. After repairs, perform confirmation test. See CONFIRMATION TEST .
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