SERVICE MANUAL UPDATE DIAGNOSTIC GUIDELINES-CODE 42

MODELS AFFECTED: 1987 SOMERSETS WITH 2.5L ENGINES (VIN CODE U) 1987-88 SKYLARKS WITH 2.5L ENGINES (VIN CODE U) 1987-88 CENTURYS WITH 2.5L ENGINES (VIN CODE R)

SERVICE MANUAL UPDATE

Some 1987-88 Buicks with 2.5L engine may experience 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, Part Number 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 of one or more of the female terminals, the connector should be replaced with the proper connector pigtail assembly kit listed in Step B below.

B. The female terminals should also be checked for looseness in the 2-way and 6-way connectors. If one or more loose terminals are found, replace the connector(s) with the proper connector pigtail assembly, as required:

2-Way Connector Pigtail Assembly Kit, Part Number 12083034 6-Way Connector Pigtail Assembly Kit, Part Number 12085247

Parts are currently available from GMSPO.

Please follow the pigtail connector assembly splicing instructions included in the kit.

NOTICE: Heat-shrinkable tubing is recomwnded for improved sealing of the spliced and soldered joints.

WARRANTY INFORMATION

Labor Operation Labor Number Time ------ ---- T1391 .5 Hours (2-Way Connector) T1392 .6 Hours (6-Way Connector) T1393 .7 Hours (Both Connectors)

Trouble Code: 92

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 1 inch (2.5 cm).

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

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

NOTICE: Connect the positive lead of the ohmmeter 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 ohmmeter may have to be changed to obtain good readings.

Use applicable labor operation number 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.