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Pcm Power & Ground Check

  1. Diagnose and clear any Diagnostic Trouble Code (DTC) that are present. Turn ignition on. Using a DVOM, backprobe between each PCM terminal C4, D4 and ground. See Fig 1 .
  2. If voltage on both terminals measure greater than 10 volts, go to step 4). If voltage on both terminals measure less than 10 volts, go to next step. If voltage on only one of the terminals measure less than 10 volts, check for open in Red wire between PCM and engine harness connector.
  3. Check 20-amp PCM/VATS fuse. If fuse is blown, check and repair short to ground in Red wire between PCM and fuse block. If fuse is okay, check and repair open in Red wire between PCM terminals C4 and D4, and fuse block. See Fig 1 .
  4. Backprobe PCM terminal D5 and ground. If voltage is greater than 10 volts, go to next step. If voltage is less than 10 volts, check 10-amp PCM fuse. If fuse is okay, repair open in Pink wire between PCM and fuse block. If fuse is blown, repair short in Pink wire between PCM and fuse block.
  5. Backprobe PCM terminals C2, C3, D2 and D3. If voltage on all terminals measure less than .1 volt, go to next step. If voltage on all terminals measure greater than .1 volt, check and repair open in Black/White wire between PCM terminals C2, C3, D2 and D4 and engine block ground.
  6. Turn ignition off. Disconnect and check contacts in PCM connectors "C" and "D". Measure resistance between PCM harness connector terminals C2, C3, D2, D3 and ground. If resistance on all terminals measure less than 5 ohms, go to next step. If resistance on all terminals measure greater than 5 ohms, repair open in Black/White wire between PCM harness connector and engine block ground. If only one of the terminals measure greater than 5 ohms, repair open in that particular circuit.
  7. Reconnect PCM harness connectors "C" and "D". Turn ignition on. Using a DVOM, backprobe between PCM harness connector terminals C12, C13 and ground. If both terminals measure 1-4 volts, check PROM contact. If PROM is properly seated, check for faulty PCM. If either terminals measure less than one volt or greater than 4 volts, perform diagnostic system check using Tech 1 scan tester.
Fig 1: PCM Power & Ground Circuit (Aurora)
G95F12562Courtesy of GENERAL MOTORS CORP.
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