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Test I: No Communication With Powertrain Control Module

  1. Turn ignition switch to LOCK position. Disconnect Powertrain Control Module (PCM) harness connector C421. Measure voltage at terminal No. 55 (Orange/Yellow wire) at PCM harness connector C421. See Figure . If battery voltage exists, go to next step. If battery voltage does not exist, repair power distribution circuit as necessary. See POWER DISTRIBUTION article in WIRING DIAGRAMS.
  2. Turn ignition switch to RUN position. Measure voltage at terminals No. 71 and 97 (both Green/Yellow wires) at PCM harness connector C421. If battery voltage exists at both terminals, go to next step. If battery voltage does not exist at both terminals, repair PCM power relay power distribution circuit. See POWER DISTRIBUTION article in WIRING DIAGRAMS.
  3. Turn ignition switch to LOCK position. Measure resistance between ground and terminals No. 24, 51, 77 and 103 (all Black/Yellow wires) at PCM harness connector C421. Measure resistance between ground and terminal No. 25 (Black/Red wire) at PCM harness connector C421. If all resistance readings are 5 ohms or less, repair module communication concern. See MODULE COMMUNICATIONS NETWORK - COUGAR article. If any resistance reading is greater than 5 ohms, repair open in appropriate wire. See GROUND DISTRIBUTION article in WIRING DIAGRAMS.
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