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Questions and Answers

Jeep Cherokee Check Engine Light

Q. 1992 Jeep Cherokee 4.0 liter 6 cylinder, 120,000 and automatic transmission. The Check Engine Light comes on after one or two minutes of driving. I have tried to extract the fault codes as you suggested, turning the ignition switch: On-Off-On-Off-On, but nothing happens. The Check Engine Light goes out after three seconds or so.

Jeep Cherokee Check Engine Light

I have tried disconnecting the battery for five minutes to allow the computer to re-set itself in case it simply was a mis-read, but no change.

Related/unrelated?? Just prior to the light coming on, one week ago, the speedometer/odometer quit. Is this related? I thought the speedometer/odometer is mechanical, not electrical so how would the computer know?


A. You have to do the On-Off-On-Off-On thing within five seconds or it will not go into self-diagnostics. If you are sure you did the procedure correctly, then I would try having it scanned with a Chrysler scan tool. If you still don't get codes the PCM probably needs to be replaced.

With the Check Engine Light on and no speedometer, I'm willing to bet the Vehicle Speed Sensor is bad. It's pretty easy to test.

  1. Test the speed sensor with an ohmmeter. Place the ohmmeter leads on the terminals in the sensor connector.
  2. Rotate the transmission output shaft and observe the ohmmeter needle. The needle should deflect indicating the switch is opening/closing as the rotor moves past the sensor. Replace the sensor if the ohmmeter does not display any kind of reading.

Jeep Cherokee Check Engine Light

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