For 1990-2009 cars

### Circuit Description

This DTC indicates that the engine control module (ECM) received a message from the transmission control module (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 controller area network (CAN) link to the body control module (BCM), which will send a message over the class 2 link to the instrument panel (I/P) cluster to turn ON the MIL.

### Conditions for Setting the DTC

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

DTC P1780 is a type B DTC.

### Diagnostic Aids

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

DTC P1780 does not indicate a fault with the ECM.

Diagnose any TCM related DTCs first.