How to Check the Engine Light on a 1991 Honda Prelude

If the "Check Engine" light comes on and remains on after the vehicle has been started, it indicates a problem with the emissions and/or fuel injection system. You will need to check the ECU (Electronic Control Unit) for diagnostic trouble codes (DTCs). This model uses an LED light in the ECU to flash trouble codes.

Things You'll Need

• Pen
• Paper
• Code chart

Instructions

Viewing the ECU

1. Pull the carpet down from the top in the front passenger's floorboard. This will reveal the ECU. On the top edge of the protective cover you will see a window for the LED.

2. Turn the ignition on without starting the car. This will cause the LED in the electronic control unit to flash. Watch and count the flashes.

3. Write down the codes. Trouble codes 1 through 9 are shown as a series of short flashes. For two-digit codes, the first digit is indicated by long flashes followed by short flashes for the second digit. For example, a code 4 would be four short flashes. A code 17 would be indicated by a long flash followed by 7 short flashes.

4. Check for multiple codes. Multiple codes are alternated. For example, a code 4 and 17 would be shown as four short flashes (for code 4) followed by a separator pause, then one long flash followed by seven short flashes (for code 17).

Tips & Warnings

• Count the codes several times for accuracy.

References

• "Chilton's Honda Accord/Prelude 1984-95 Repair Manual"; Will Kessler, A.S.E., S.A.E.; 1995

Resources

• 2CarPros: Diagnostic Trouble Code Definition Table