Diagnostic Aids

Perform this test when instructed to or if directed by other test procedures. This test is used to diagnose the PCM.

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 ground and PCM harness connector terminal No. 48. See Figure. 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. 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 ground and PCM harness connector terminal No. 48. Measure resistance between negative battery terminal and PCM harness connector terminal No. 48. 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. 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 article. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open CTO circuit.
4. Check CTO Signal From PCM
   
   Reconnect PCM harness connector. Start engine. Using a DVOM, measure voltage between instrument harness connector CTO terminal 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.