Circuit Description
The engine control module (ECM), transaxle control module (TCM), and the body
control module (BCM) communicate with each other over the controller area network
(CAN) BUS circuits 2500 and 2501. The CAN BUS is a communications protocol that is
used by the TCM to communicate vital engine control inputs from a stand-alone engine
controller. The diagnostic checks the information received in CAN to determine whether
to pass or fail a code. Before checking the information, the TCM makes sure the CAN
messages are being received by checking the BUS failure timer.
Conditions for Setting the DTC
DTC P1779, P1791, P1792 or P1795 will set if the TCM did not receive a needed
engine parameter over the CAN BUS from the ECM when:
| • | Engine speed is greater than 500 rpm for 5 seconds and not at fuel cutoff. |
| • | System voltage between 8 and 18 volts. |
Diagnostic Aids
| • | This code does not indicate a problem with the TCM. It does indicate the
ECM is not sending the required information to the TCM. |
| • | Check for and diagnose any DTCs stored in the ECM related to the ECT,
pedal position or TP sensor circuits. |
| • | Check for any DTCs stored in the EBTCM related to the torque reduction/request
circuit. |
