2002 Mazda B2300 StandardFACTORY OEM SERVICE PROCEDURE

Tachometer Output Failure

  1. Check CTO Circuit For Short To Power

    Install breakout box, leaving PCM disconnected. With KOEO, measure voltage of CTO circuit between breakout box terminal No. 48 and ground. Turn ignition off. If voltage is less than 0.5 volt, go to next step. If voltage is 0.5 volt or more, repair short circuit. See WIRING DIAGRAMS article. Verify symptom no longer exists.

  2. Check CTO Circuit For Short To Ground In Harness

    Disconnect PCM connector. Disconnect instrument cluster 16-pin connector C214. Measure resistance between breakout box terminal No. 48 (CTO SIG circuit) and terminals No. 51, 76, 77 or 103 (PWR GND circuits) and chassis ground. Record readings. Measure resistance between breakout box terminal No. 48 (CTO SIG circuit) and chassis ground. Record reading. If both resistance readings are more than 10,000 ohms, go to next step. If either resistance reading is 10,000 ohms or less, repair short in wiring harness. See WIRING DIAGRAMS article. Verify symptom no longer exists.

  3. Check CTO Circuit For Open Harness

    Measure resistance of CTO circuit (Tan/Yellow wire) between breakout box terminal No. 48 and instrument cluster 16-pin connector terminal No. 15. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open circuit. See WIRING DIAGRAMS article. Verify symptom no longer exists.

  4. Check CTO Signal From PCM

    Connect PCM connector. With KOER, measure voltage of CTO circuit (Tan/Yellow wire) between instrument cluster 16-pin connector terminal No. 15 and ground. If voltage is 3-9 volts, see appropriate INSTRUMENT PANEL article in ACCESSORIES & EQUIPMENT. If voltage is not 3-9 volts, an open or short is present in PCM. Replace faulty PCM. Verify symptom no longer exists.
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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.

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