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HOMESERVICE MANUALSPONTIAC1983GRAND PRIX BASE, 5.0 HREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 11 (FEEDBACK CARBURETOR TESTS W/CODES)CODE 42: ELECTRONIC SPARK TIMING (EST)NOTES
1983 Pontiac Grand Prix Base, 5.0 H

Code 42: Electronic Spark Timing (Est): Notes

1983 Pontiac Grand Prix Base, 5.0 HSECTION Notes
WARNING: This page does not describe the selected car, but rather 28 other vehicles, including the 1984 Pontiac Phoenix, 1984 Pontiac Parisienne, 1984 Pontiac Grand Prix, 1984 Pontiac Firebird, and 1984 Pontiac Bonneville. However, it is still accessible from the selected car via links, so may be relevant.

Code 42 says that the ECM has seen:

  • Open or grounded By-pass Circuit (term. "11").
  • Open or grounded EST Circuit (term. "12").

With a grounded EST Circuit, the engine may not run. A grounded EST may sometimes not set a code unless cranked 10 seconds or longer with circuit grounded.

NOTE: The following step numbers refer to the numbers in the accompanying flow chart(s).
  1. This checks operation of EST. Grounding the "test" terminal causes timing to go to a fixed value which is normally different from that obtained with EST operating. Therefore, the timing should change. Usually the change can be heard in engine RPM. If so, the timing change does not have to be checked.
  2. This step eliminates the ECM and ECM connections from the module input. By jumpering terms. "A" and "B", the distributor reference signal is fed directly into the EST line of the module. By putting voltage through the test light on term. "C" of the harness, the module is switched to the EST mode and the vehicle should run. If the engine stops, there is no EST signal reaching the module due to open or poor connections, or the module is faulty.
  3. By removing the jumper, you are opening the EST signal, and the engine should stop.
  4. The engine ran when the module was jumpered. The problem is not in the distributor (if the correct HEI module is installed). The wrong HEI module can set a Code 42.
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:

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