INTERMITTENT OR HARD CODE 25 PERFORM A GROUND TEST

VEHICLES AFFECTED: 1982 DEVILLE, BROUGHAM, ELDORADO AND SEVILLE

Code 25 on 1982 Cadillacs equipped with an HT4100 engine is designed to detect instances when the HEI ignition module is not in control of the electronic spark timing (EST) line, circuit 423. If the ECM detects voltage on the EST circuit when in bypass mode, it assumes that the EST circuit is open and code 25 is set. Code 25 turns the check engine light on and causes the HEI system to operate on backup spark timing built into the HEI distributor module. After the code is set, the HEI system will run in backup spark mode until the ignition is turned off.

Poor ground connections from the ECM to the right cylinder head can cause the ECM to read improper voltage on the EST circuit when in bypass and set a false code 25. To determine if the code is being set falsely, perform the following ground test.

1. Disconnect the distributor four-way, C432, connector.

2. Connect the positive (+) lead of a voltmeter to the engine harness side of the open connector, pin D.

3. Connect the negative (-) lead of the voltmeter to the negative (-) battery terminal.

4. Crank the engine and record the voltage.

If the voltage is greater than 0.9 volts, a poor ground connection should be suspected. Check the following connections:

- ECM ground terminal, G335, at the right cylinder head. It should be clean and tight with a star washer underneath the ring terminal.

- circuit 450 at the centre bulkhead connector, C101, cavity AX.

- circuit 450 at the environmental connector, C106, cavity V.

- circuits 450 and 453 at pins 1, 2, and 17 of the blue Pl ECM connector.

- check for opens in circuit 450 or 453 wiring.

If the voltage is less than 0.9 volts, refer to page 8DI-34 of the 1982 Electrical Information Diagnosis Manual - Final Edition.

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.