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Home › Ford › 2003 › Excursion 7.3 F, 4WD › Repair and Diagnosis › Engine Performance › System › Engine Controls - System Test JE Through Z - CNG, Flex-Fuel & Gasoline › Test JH: Tachometer Output Failure › Testing

Test JH: Tachometer Output Failure: Testing

  1. 1) Check CTO Circuit For Short To VPWR In Harness

    Turn ignition switch to OFF position. Disconnect PCM connector. Inspect connector for loose, damaged or corroded terminals. Turn ignition switch to ON position. Using a DVOM, measure voltage between chassis ground and PCM harness connector terminal No. 48. See PCM CONNECTOR IDENTIFICATION . If voltage is less than .5 volt, go to next step. If voltage is .5 volt or more, repair short to VPWR in CTO circuit.

  2. 2) Check CTO Circuit For Short To Ground In Harness

    Turn ignition switch to OFF position. Disconnect instrument cluster connector. Using a DVOM, measure resistance between PCM harness connector terminal No. 48, chassis ground and negative battery terminal. If both resistance measurements are more than 10 k/ohms, go to next step. If either resistance measurement is 10 k/ohms or less, repair short to ground in CTO circuit.

  3. 3) Check CTO Circuit For Open In Harness

    Using a DVOM, measure resistance of CTO circuit between PCM harness connector terminal No. 48 and instrument cluster harness connector. See WIRING DIAGRAMS . If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open CTO circuit.

  4. 4) Check CTO Signal From PCM

    Reconnect PCM harness connector. Start engine. Using a DVOM, measure voltage between CTO circuit at instrument cluster harness connector and negative battery terminal. If voltage is not 3-9 volts, replace PCM. If voltage is 3-9 volts, CTO signal from PCM is okay. Check instrument cluster and repair as necessary. See appropriate INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT.
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