Question about 1999 Jeep Grand Cherokee
The problem is an automatic transmission malfunction.
P0783 means 3-4 shift malfunction. The code is returned when the PCM does not detect decrease in engine revs after shifting from third to fourth gear.
If the problem happened only once, it may have been a temporary malfunction. If you keep getting the fault code, and you notice transmission problems (hanging in third for too long or wrong shifting), then the transmission must be repaired.
The most common cause for the problem is a faulty transmission shift solenoid in the solenoid pack located in the the valve body, in the transmission. The solenoids are tested accessing valve body and solenoid pack and reading Ohms at single solenoid contacts. When the solenoid is faulty it reads open.
Other faults that return P0783 are faulty transmission relay, faulty TCC solenoid, faulty gp solenoid, and faulty PCM (very unlikely). Here a diagram showing all parts involved:
Posted on Feb 10, 2011
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