Engine Controls - Updated Code 42 (EST) Diagnostic Chart
88buick13Bulletin: 88-6E-19
Date: Aug., '88
Ref. No.: 88-218-6E
Corp. Ref. No. 836532
SUBJECT: CODE 42 SUPPLEMENTAL DIAGNOSTIC GUIDELINES AND REPAIR PROCEDURES SERVICE MANUAL UPDATE
MODELS AFFECTED: 1987-88 CENTURYS WITH 2.5L ENGINE (VIN CODE R) 1987-88 SKYLARKS WITH 2.5L ENGINES (VIN CODE U)
1987 SOMERSETS WITH 2.5L ENGINES (VIN CODE U)
SERVICE MANUAL UPDATE
Some 1987-88 Centurys, Skylarks, or Somersets 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-2, 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, Part Number 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 Corporate Bulletin 86-8-10 or 88-8-6 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 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, then 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 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 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 and time per the Labor Time Guide.