How do you check a 1989 Cadillac deville engine light?

A 1989 Cadillac DeVille doesn't have a standard "check engine light" in the same way modern cars do. Instead, it uses a system of diagnostic codes displayed through a series of blinks from a light, usually located on the instrument panel. This light is often referred to as the "Service Engine Soon" light, but it's not the same as the OBD-II system in later cars.

To check for trouble codes:

1. Locate the diagnostic connector: This is a two-terminal connector usually under the dashboard. The exact location varies slightly depending on the model year and trim level, but consult your owner's manual for the precise location. If you don't have a manual, online resources for 1989 Cadillac DeVille repair manuals might help.

2. Obtain a jumper wire: You'll need a small piece of insulated wire (paperclip works in a pinch, but is less ideal).

3. Jump the terminals: Connect the jumper wire to the two terminals in the diagnostic connector. This completes a circuit allowing the system to output diagnostic codes.

4. Monitor the light: With the ignition key turned to the "ON" position (not started), observe the check engine light (or whatever light represents the system). It will flash a series of short and long blinks.

5. Record the code: Each series of blinks represents a digit in the trouble code. For example, one long blink followed by two short blinks represents the digit "12." Note down the sequence for each group of blinks. The system will repeat the codes for verification. Write down each sequence until you have all codes.

6. Consult a manual: Once you've recorded the code(s), you'll need a 1989 Cadillac DeVille repair manual or a suitable online resource (like a Haynes manual or a repair website) to decipher the codes and find out what the problem is. This is crucial because the codes are not standardized like in later OBD-II systems.

Important Considerations:

* Safety: Always disconnect the battery's negative terminal before working on any electrical system in your vehicle to prevent short circuits.

* Accuracy: The jumper wire method is less precise than modern diagnostic scanners.

* Manual: Obtaining a repair manual specific to your 1989 Cadillac DeVille is highly recommended for proper interpretation of codes and repair procedures.

This process is significantly different from modern OBD-II systems. If you're uncomfortable performing this procedure, taking your vehicle to a qualified mechanic is the safest and most reliable option.