Diagnostic Aids

Perform this test when instructed to or if directed by other test procedures. This test is used to diagnose the Powertrain Control Module (PCM).

1. 1) Check CTO Circuit For Short To Power In Harness
   
   Turn ignition switch to OFF position. Disconnect PCM connector(s). Inspect connector for loose, damaged or corroded terminals. Turn ignition switch to ON position. Measure voltage between PCM connector terminal No. 48 and chassis ground. If voltage is less than .5 volt, go to next step. If voltage is .5 volt or more, repair short to power in CTO circuit.
2. 2) Check CTO Circuit For Short To Ground In Harness
   
   Turn ignition switch to OFF position. Disconnect appropriate instrument cluster connector which has CTO circuit terminal. See appropriate INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT for connector identification and wiring diagram. Measure resistance between PCM connector terminal No. 48 and chassis ground. If resistance is more than 10 k/ohms, go to next step. If resistance is 10 k/ohms or less, repair short to ground in CTO circuit.
3. 3) Check CTO Circuit For Open In Harness
   
   Measure resistance of CTO circuit between PCM connector terminal No. 48 and appropriate instrument cluster harness connector. 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 connector. Start engine. Measure voltage between CTO terminal at instrument cluster harness connector and negative battery terminal. If voltage is not 3-9 volts, replace PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Program PCM. See FLASH VEHICLE IDENTIFICATION BLOCK PROCEDURE . 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.