For 1990-2009 cars

# CODE 42 DIAGNOSIS GUIDELINES SERVICE MANUAL UPDATE

CODE 42 SUPPLEMENTAL DIAGNOSTIC GUIDELINES AND REPAIR PROCEDURES SERVICE MANUAL UPDATE

#### VEHICLES AFFECTED: 1987-88 A/N/P CARS W/2.5L ENGINE

Some 1987-88 A, N or P cars with the 2.5L engine may experience a Code 42. The following information is supplemental to the diagnostic chart in the service manual Section 6E2-A-49, Code 42 Electronic Spark Timing (EST) Circuit - 2.5L engine. When diagnosing the condition, the following additional guidelines are recommended to assist in correcting the condition.

(1). A. The wire harness female terminals in the 2-way and 6-way connectors to the DIS module should be checked for proper contact. Make sure the female terminals grip the male terminals firmly. Test the grip by inserting a separate male terminal, P/N 12047581 from dealer stock, into a female terminal. With the male terminal inserted, turn the female connector upside down. If the male terminal falls out, then the female terminal should be replaced with a new terminal, P/N 12047680. Repeat this test for each female terminal in the connectors.

B. The female terminals should also be checked for looseness in the 2-way and 6-way connectors. If loose terminals are found replace the parts as required.

#### NOTICE: REFERENCE BULLETIN #86-8-124 OR 88-8-117 FOR PROPER TERMINAL SERVICING PROCEDURES.

C. Finally, the wire harness leading into the 2-way and 6-way connections at the DIS module should be checked to make sure that it is not too close to the spark plug wires. If the harness is close to the spark plug wires, the wire harness must be rerouted away from the spark plug wires at least 2.5 cm (1.0 inch).

(2). With the engine running and Code 42 cleared, lightly tap by hand on the outside case of the ECM. If Code 42 sets, then replace the ECM.

(3). When checking for a change from by-pass to EST modes, the current diagnostic procedure specifies less than 500 ohms between the ECM harness at CKT 423 and ground, and switches to over 5000 ohms when a test light connected to 12 volts touches CKT 424.

#### NOTICE: CONNECT THE POSITIVE LEAD OF THE OHM METER0338 TO EST CKT 423 AND THE NEGATIVE LEAD TO GROUND.

The values of 500 and 5000 ohms are not critical - just that a switch from "hundreds" to "thousands" of ohms occurs.

#### NOTICE: THE SCALES ON THE OHM METER MAY HAVE TO BE CHANGED TO OBTAIN GOOD READINGS.

Use applicable labor operation and time per the Labor Time Guide.

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.