Jeep Wrangler engine codes 21 and 42 signify a problem with the oxygen sensor or automatic shutdown relay, respectively. The 55 engine code signifies the end of code display from the check engine light.Continue Reading
A slow response of the upstream oxygen sensor can lead to the 21 Jeep Wrangler code. Other probable causes of the code are circuit malfunctions of the upstream or downstream oxygen sensor heating elements, or low oxygen sensor voltage. The code may also appear if the input voltage to the downstream oxygen sensor remains above the normal operating range or temperature.
A 42 Jeep Wrangler code appears when the system detects a shorted or open condition in the auto shutdown relay circuit. Alternatively, the code may signify a shorted or open condition in the relay control circuit of the fuel pump. An open circuit or short circuit between the fuel gauge sending unit and the power train control module, or the absence of movement in the fuel level sender, may also cause the code to appear.
For the Jeep Wrangler 1991 through 1995 models, the check engine light helps to diagnose the trouble codes. Troubleshooting involves turning the ignition key to the on position, off position, on position, off position and finally back to the on position without starting the engine. The check engine light then flashes the number of the first digit, pauses, and flashes the number of the second digit for any code stored in the power train control module memory.Learn more about Car Makes & Models