O/D Off Indicator Remains Lit

"OD/OFF" Indicator Remains Lit:

"OD/OFF" Indicator:

CIRCUIT DESCRIPTION

When the OD Switch button is released, a signal is sent to the Transmission Control Module (TCM). The TCM turns on the "OD/OFF" indicator lamp in the instrument panel cluster, informing the driver that the transmission will not shift into overdrive. If the button is depressed, the TCM receives a signal, the "OD/OFF" indicator lamp goes out and the transmission is allowed to shift into overdrive (4th gear) when appropriate.

The "OD/OFF" indicator also will flash on and off to alert the driver that a problem has occurred with the transmission and that the vehicle should be taken for service. At the same time, it is also used by a technician to identify any Diagnostic Trouble Codes (DTCs) stored in the TCM memory by code flashing method.


TEST DESCRIPTION

Numbers below refer to the circled numbers on the diagnostic chart.

1. Checks for a short to ground in wire between the TCM and I/P gauge cluster.

2. Checks for a defective (constantly open) OD Switch.

3. Determines whether the condition was caused by a short to ground in wire between the TCM and the OD switch and not by a faulty TCM.


DIAGNOSTIC AIDS

Check fuses for opens, and grounds for clean and tight connections.

An intermittent condition may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.

Check for poor connections at component and inline harness connector terminal for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and for poor terminal-to-wire connections before replacing components. After repairs have been made, repeat the TCM OBD System Check to ensure the system is functioning normally.