ON-CAR HEI MODULE TEST IF MODULE TESTER INOPERATIVE

VEHICLES AFFECTED: 1982-1985 RWD DEVILLE AND FLEETWOOD BROUGHAM, 1985-1988 DEVILLE AND FLEETWOOD, AND 1982-1988 ELDORADO AND SEVILLE

During a recent analysis of inoperative ignition modules, a dealer submitted an alternate test procedure for diagnosing HEI ignition modules. The test described below requires the use of only three jumper leads and a 12V electrical test light. It is presented here for use solely in the event that an approved module tester, such as the Kent-Moore tester J24642-F, is damaged or otherwise unavailable. Use of an approved module tester is still recommended as the primary diagnostic tool for ignition modules. Refer to Section 6E-C4, "Electronic Spark Timing (EST) System" and Section 6D4, "Ignition System" of the appropriate model year Service Information Manual for additional information.

ON-CAR HEI MODULE TEST CADILLAC DFI MODELS ONLY

1. Open the 4-way connector at the distributor wire harness.

2. Using two jumper leads reconnect the distributor reference line, circuit 430 (purple/white) and the distributor ground, circuit 453 (black/red).

3. Start the engine. A code "23" will set because the engine is running on Base Timing. If the engine will not start or stalls after start, refer to Chart A-3 in Section 6E-A of the Service Information Manual.

4. Connect a test light to 12V and probe pin "C", circuit 424 (tan/black) on the distributor side of the 4-way connector. Applying 12V to the bypass line drives the HEI module into the EST mode. With the EST line, circuit 423 (white) open, the engine should die. If the engine quits, bypass circuit operation of the HEI module is verified.

NOTE: Battery and cranking motor must be operating correctly to reach proper rpm.

5. On the distributor side of the 4-way connector jumper the EST line, circuit 423 (white) to distributor reference circuit 430 (purple/white). With the test light still applying voltage to the bypass line, circuit 424, start the engine. Engine operation verifies that the EST circuit in the HEI module is operating normally.

6. Remove the test light while the engine is running. If the engine quits, EST grounding in the HEI module is verified. When voltage is removed from the bypass line, the module grounds the EST circuit internally. Since the EST line was jumpered to the distributor reference signal, the reference signal will be grounded causing the engine to quit.

7. If any of the above tests fail, inspect the distributor wiring for shorts or opens. If O.K., replace the ignition module.

8. Remove all jumper leads and reconnect the distributor 4-way connector.

9. Enter diagnostics and clear code 23.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.