ECM - Driveability Concerns/Erratic Warning Lamps: Overview
84cadillac03Bulletin No.T 84-92
File In Group 6C
Number 82
Date Aug. '84
SUBJECT: TELLTALE LIGHTS AND/OR DIGITAL DISPLAYS ERRATIC OR FLASHING, CRUISE DISENGAGES
MODELS AFFECTED: 1980-1985 CADILLACS EQUIPPED WITH DEFI, DFI, CCC OR CIMARRON EFI
A number of engine performance conditions, usually of an intermittent nature, can be caused by disturbances in other parts of the vehicle's electrical system. Voltage surges, intermittant opens and voltage transients can indirectly affect ECM or DFI system operation. Symptoms may include flashing or erratic telltale lamps and/or digital displays, engine quits, idle surges, poor performance, or disengagement of Cruise Control. This condition is sometimes called an ECM reset since these disturbances may cause erratic ECM operation until the ECM recognizes the fault, and "resets" itself, and resumes correct operation. Such erratic operation is usually of a temporary nature and does not damage the ECM.
This bulletin summarizes possible causes of ECM resets, and provides specific information relating to each of these possible causes. The following causes of ECM resets may not be all inclusive, and are not meant as a step-by-step diagnostic procedure. Use your knowledge of the vehicle's history and observation of any unusual vehicle equipment or replacement parts as a guide in diagnosis.
When diagnosing an ECM reset, you should first assure yourself that it is not an authentic intermittent code in the case of "Check Engine," or "Service" lights, or a simple ECC or fuel data circuit problem if the comment is intermittent displays.
When diagnosing an ECM reset, keep in mind that an resets originate as:
1. Power and ground loss to ECM.
2. Large voltage variations on ECM connected power and ground wires.
3. Large voltage variations or transients causing false signals on ECM connected low voltage signal line.
The vehicle history will often lead to a fix. Try to determine:
1. When did the condition begin?
2. Were any accessories recently added?
3. Was the car recently "tuned up"?
4. Was the car rebuilt after a theft or collision damage?
5. Has the car had a starter, generator or battery replaced recently?
6. Has there been heavy engine work done that may have disturbed power, grounds or sensor connections?