The Check Engine Light (CEL), also known as the Malfunction Indicator Lamp (MIL), is a dashboard indicator that illuminates when the Engine Control Unit (ECU) detects a malfunction in the engine or emissions control systems.

Retrieving Diagnostic Trouble Codes#

When the CEL is active, the ECU stores diagnostic trouble codes (DTCs) that can be retrieved to identify the cause of the fault.

OBD0 Systems (1988–1991)#

OBD0 ECUs feature an LED indicator mounted directly on the ECU circuit board:

1. Locate the ECU (typically under the passenger footwell).
2. Observe the blinking red LED through the circular viewing window in the ECU case.
3. Count the flashes to determine the error code.

OBD1 Systems (1992–1995)#

OBD1 systems utilize the dashboard CEL to flash the error codes:

1. Locate the 2-pin Service Connector (SCS) (typically behind the passenger-side kick panel).
2. Jump the pins together using a jumper wire or paperclip.
3. Turn the ignition to the ON position.
4. Observe and count the flashes on the dashboard CEL.

Importance of Diagnostics#

The CEL should never be ignored. It serves as the primary interface for communicating electrical or mechanical faults, ranging from minor sensor issues to critical engine malfunctions. Always retrieve and document the code before attempting repairs.