Transmission Diagnosis

This DTC indicates that the ECM received a message from the TCM to turn On the MIL (SERVICE ENGINE SOON) telltale due to a transmission related OBD II failure. The ECM will send a message via the CAN link to the BCM, which will send a message over the Class II link to the I/P cluster to turn On the MIL.

DTC PARAMETERS
DTC P1780 will set when the ECM received a MIL request message from the TCM over the CAN link.

P1780 is a (type B) DTC

DIAGNOSTIC AIDS
DTC P1780 does not indicate a fault with the CAN link circuit.

Diagnose any TCM related DTCs first.


P1779 - Engine Torque Delivered To TCM Signal
P1780 - Torque Reduction Signal
P1791 - Throttle/pedal Position Signal
P1792 - Engine Coolant Signal
P1795 - Throttle Body Position Signal





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.

DTC PARAMETERS
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.