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HOMESERVICE MANUALSTOYOTA2004CELICA GT, STANDARDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 139 (CRUISE CONTROL SYSTEMS)DIAGNOSTIC TESTSDTC 21: VEHICLE SPEED SENSOR CIRCUITDIAGNOSTIC PROCEDURE
2004 Toyota Celica GT, Standard

Diagnostic Procedure

2004 Toyota Celica GT, StandardSECTION Diagnostic Procedure
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. Perform speedometer input signal check. See STEP 4 of Cruise Control Input Signal Check. See Figure. If CRUISE indicator light operates as described, go to step  5. If CRUISE indicator light does not operate as described, go to next step.
  2. Check speedometer circuit. See INSTRUMENT PANELS - AVALON article. If speedometer circuit is okay, go to next step. If speedometer circuit is defective, repair as required or replace instrument cluster. After repairs, perform confirmation test. See CONFIRMATION TEST .
  3. Turn ignition off. Disconnect cruise control ECU 16-pin electrical harness connector and instrument panel 28-pin electrical harness connector. Using a DVOM, check for open and short circuit conditions in Violet/White wire between cruise control ECU 16-pin electrical harness connector terminal No. 12 and instrument panel 28-pin electrical harness connector terminal No. 18. See Figure. Also check wires, harnesses and connectors between instrument panel and vehicle speed sensor. Wire colors and electrical harness information are not available from manufacturer for vehicle speed sensor. If wires, harnesses and connectors are okay, go to next step. 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 .
  4. Check vehicle speed sensor. See appropriate TEST NO. 2: SPEEDOMETER DOES NOT OPERATE under SYSTEM TESTS under INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. If vehicle speed sensor is okay, go to next step. If vehicle speed sensor is defective, replace vehicle speed sensor. After repairs, perform confirmation test. See CONFIRMATION TEST .
  5. 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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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.