XJ Jeep

Taken from NAXJA post
So, before outlining the proceedure (a.k.a. “key trick”) to get the codes, a few things to note:
1) You may have to set the parking brake for the codes to show
2) On older models, the blink-spacing is not always perfectly uniform, so if you see 23 23, it’s probably just a single 55 since codes are not repeated (55 is end of codes – it’s normal)
3) On newer models with a digital odometer, the codes are usually displayed on the odometer rather than blinking the check engine light.
4) When the computer indicates major failure, it can activate “Limp In” mode, which guesses about data to compensate for sensor failure, allowing you to get the car to a mechanic. One major symptom of this is losing third and/or fourth gear on autos.

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