Chart A6: Won't Flash Code 12 Test

1984 Pontiac 6000 STESECTION Chart A6: Won't Flash Code 12 Test
NOTE: The following step numbers refer to the numbers in the accompanying flow chart(s).
  1. This step checks for short to battery voltage in wire to term. "C" or faulty lamp driver. Normal reading is 9 to 11 volts.
  2. This step checks to see if problem is related to the ECM or lamp driver. Grounding term. "C" should turn lamp "OFF".
  3. Grounding term. "G" at ECM and finding light "ON" indicates an open in the wire to term."C" of lamp driver. Grounding term. "G" should turn lamp "OFF".
  4. This step checks for open in wire from ECM to test terminal in ALDL connector. The lamp should flash Code 12 when term. 5" is grounded.
  5. This checks for proper voltage supply to ECM, both should read over 9 volts. Term. "C" is ignition and term. "R" is constant battery for long term memory.
  6. This test checks for bad ground in ECM. Terms. "A" and U" are connected together in the ECM.
  7. This step distinguishes between a faulty ECM and PROM. Normal response is for Code 51 to flash even though the PROM is not installed in the ECM. If no Code 51, ECM is faulty.
Fig 1: Chart A6: Won't Flash Code 12 Flow Chart
G9303
RENDER: 1.0x

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • β€’ You smell fuel, burning insulation, or see smoke.
  • β€’ Brakes feel soft, pull hard to one side, or make grinding noises.
  • β€’ The engine overheats, stalls repeatedly, or misfires under load.
  • β€’ You are missing required tools, torque specs, or safe lifting equipment.
  • β€’ You are not confident in the next step or safety outcome.