P1788

DIAGNOSTIC TROUBLE CODES P1786, P1787 AND P1788
THROTTLE POSITION SIGNAL FROM THE TRACTION CONTROL SYSTEM, SIGNAL TOO LOW OR TOO HIGH/OPEN CIRCUIT OR SHORT CIRCUIT TO GROUND OR BATTERY POSITIVE VOLTAGE AND SIGNAL WRONG

Fault Symptom.
Hard gear shifting when the TCS function is activated.

Conditions.
Diagnostic trouble code P1786 is recorded if the TCS throttle position signal from the TCS ECM is wrong or outside permitted limits for more than 4 seconds.

Diagnostic trouble code P1787 is recorded if the TCS throttle position signal from the ECM is short-circuited to ground or if there is an open circuit.

Diagnostic trouble code P1788 is recorded if the TCS throttle position signal is short-circuited to the battery's positive terminal.

Diagnostic Procedure.
The signal is only found in the V-6 variant and is a 122 Hz PWM signal which states the opening angle of the TCS throttle.

1. If the TCS-lamp is on as well, read and remedy the fault code in the TCS system. If the fault code is still there, go to step 2.

WARNING: In order to activate the TCS function the car can be run on a lifting device. If this mode is used you must exercise the utmost care. If only the front of the car is lifted up and placed on trestles, the hand brake should always be applied and no one be allowed in front of the car or near the front wheels during the inspection. The speed should be kept as low as possible but over 4 km/h.





2. Connect ISAT scan tool to the car's data link connector.

Contact the transmission system with ISAT and look up TCS ACTIVE under the READ ON/OFF menu.

Activate the TCS function by running the car with the front lifted up and check that the display text on ISAT changes from TCS OFF to TCS ON at the same time as the TCS lamp comes on.

If this is not the case, check the wiring between TCS control module pin 12 and TCM pin 4 for any open circuit/short circuit.

3. Contact the transmission system with ISAT and look up TCS THROTTLE POS under the READ FUNCTIONS menu.

Check that the throttle position is about 70-92% when at a standstill and that it changes to a considerably lower value when the speed of the front wheels exceeds 4 km/h.

If the measurement result is correct, go to step 4.

If the measurement result is wrong, check and remedy the cable between TCS control module pin 4 and TCM pin 15 for an open circuit/short circuit.

4. Clear the fault code, start and test-drive the car and check if the fault code reappears.

If a fault code is recorded, go to "Actions Before Changing a TCM".