CHECK GEARBOX indicator lamp: Notes

Fig 1: Gearbox Indicator Lamp Communication Diagram

Courtesy of SAAB-SCANIA OF AMERICA, INC.

Fig 2: Gearbox Indicator Lamp Circuit Diagram

Courtesy of SAAB-SCANIA OF AMERICA, INC.

If there is a fault in the automatic transmission or its control module, the TCM lights the CHECK GEARBOX warning lamp in the main instrument unit.

The lamp is powered from the main instrument unit and grounded internally by the main instrument unit. TCM continuously sends bus information CHECK GEARBOX, unit ON/OFF.

On receiving CHECK GEARBOX ON, the control module grounds the output of the lamp which then lights up.

When the TCM sends the message CHECK GEARBOX OFF, the lamp goes out.

When the ignition is turned on, the TCM lights the lamp for approx. 3 seconds and if there is no fault the lamp will go out.