Monday, May 22, 2006

Check engine light codes P0123 and P1596 for 1999 Jeep Cherokee

Beware when you see these 2 codes together on 1999 Jeep Cherokee. It is misleading because if you break down the meaning of each code:

P0123 is a failure in the tps circuit where signal voltage is higher than maximum setting.
P1596 is a failure in the cruise control circuit where the speed control switch is always high

Basic Concept:

On 1999 Cherokee, both the TPS sensor and the speed control switch are connected together thru a common brown yellow wire. This is a ground wire located at the right rear of the engine. However, this ground wire also passes the clock spring assembly located in the steering column. This clock spring is a triggering devise that helps activate the airbag and the speed control switch which sends a signal to the engine power train. This can be better understood if you have a wiring diagram of the cruise control circuit which shows in detail the various circuit flows of these components.

In layman’s language, as long as both tps and cruise control codes appear together, don’t try to fix this as if they are separate codes. Example; trying to replace the tps sensor and then fixing the cruise control circuit next are a no, no. The best approach to this is to monitor the signal voltage of the tps sensor and try disconnecting the clock spring terminals. If the clock spring is the culprit, the tps voltage should return to normal.


When working on the clock spring, beware that the airbag could accidentally deployed and can cause injury. Please consult your service manual or authorized Jeep dealer.


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