1) Fix the known problem
2) If the bucking continues, Test the TPS and wire harness
3) If the bucking continues, test the O2 sensors and wire harness
Disconnecting the clock spring may eliminate the symptoms and confirm a clock spring diagnosis.
COMPLAINT: TPS CODE P0123 WILL NOT CLEAR
A late model Jeep with a 2.5 or 4.0 liter engine and the AW4 transmission comes in with the “MIL” Check Engine Light illuminated and a complaint of late shifts. A scan reveals a code P0123, “TPS Voltage High”, is stored. The scan tools data list indicates that the TPS signal wire voltage is at 5.0 volts at closed throttle, and then ranges up to 11.5 volts. A back probe of the TPS signal wire (usually is an Orange/Dk Blue wire), shows 5.7 volts at closed throttle, with a similar rise in voltage as the throttle is opened. A check of the TPS 5 volt supply and ground circuit prove that both of these circuits are good.
A check of the TPS signal wire with the TPS disconnected shows the same 5.7 volts. Inspection of the wiring between the TPS and the PCM and TCM shows no faults. A replacement TPS does not cure the problem, neither does replacement of the PCM or TCM.
CAUSE:
The Switch Sense circuit in the Clock spring in the steering wheel hub has shorted to battery voltage from the horn button circuit. When the Switch Sense Circuit shorts to the 12 volt HORN circuit the TPS signal voltage is driven high and remains there as shown. This is because the 5 volt reference voltage used by the Cruise Control “Switch Sense” circuit and the TPS are shared inside the PCM.
CORRECTION:
Replace the Clock spring assembly. Once the Clock spring has been replaced, be sure to check the sensor 5volt reference voltage at the PCM to insure that circuit has not been damaged by the short to power. Also check the TPS signal range to insure the TPS has not been damaged.
