Vehicles older than 1995 models typically feature the OBD-1 trouble-code system; cars made after 1995 usually have the OBD-2 system. The differences between the two systems are that the older codes contain two digits, while the new codes begin with a letter indicating what system in the engine is malfunctioning, followed by a series of numbers (see Resources). The key "On/Off" method works on older vehicles; the digital dash and jumper-wire methods work for newer vehicles.
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Things you need
- Ignition key
- Jumper wire
- Paper clip
Insert the key into the ignition. Turn the car on and off quickly, ending with the key in the "On" position. How many times you need to do this depends on the engine; some require three times, some five, others more. Don't crank the engine during this sequence or you'll have to begin again.
Watch the "Check Engine" light on the dash. Once the sequence has been initiated, the "Check Engine" light begins to flash. Each flash represents a number in a two-digit trouble code stored in the computer. A pause separates the first digit from the second digit. For instance, the code "23" flashes as follows: flash, flash, pause, flash, flash, flash.
Record the codes as they flash. Check with your owner's or service manual for the meanings of the codes. Each manufacturer has a different set of codes and meanings.
Locate the diagnostic test link where a scan device plugs in, usually found under the dash on the driver's side. If the link has 12 ports rather than 16, connect ports "A" and "B" with a paper clip or jumper wire. Watch the "Check Engine" light for codes as documented previously.
Turn the key to the "On" position while simultaneously depressing the odometer "Trip" and "Reset" buttons if your dash cluster is digital. The trouble codes read from the odometer display in this method.
Depress the odometer "Trip" and "Reset" buttons while turning the car on and off several times, ending with the key in the "On" position. Release the odometer buttons. The odometer will count down, then display the trouble codes in certain models.
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