Service Transmission Lamp (STL)

The Transmission Control Module (TCM) controls a dedicated Service Transmission Lamp (STL) which illuminates when certain non-emissions driveability conditions which relate to the TCM diagnostics report a fail. The Service Transmission Lamp (STL) is located in the Instrument Panel Cluster (IPC).

The TCM has no direct control of the engine MIL, but if a transmission fault occurs that is emissions related, the engine MIL must illuminate. A MIL Request circuit between the ECM and the TCM provides a means for illuminating the MIL, even though the fault was detected by the TCM. This circuit is pulled up to B+ within the ECM. In order to illuminate the MIL, the TCM pulls the circuit low. The ECM detects this and DTC P1700 is set (in the ECM), which illuminates the MIL.