General

The control module has an integrated diagnostics system, Volvo On-board Diagnostics (OBD). The Transmission Control Module (TCM) continuously monitors its own functions and the in/out signals in the system. If the TCM detects a malfunction it stores a Diagnostic Trouble Code (DTC) and the combined instrument panel warning lamp flashes. There are exceptions, see DTC Table found under Testing and Inspection. When a DTC is stored the system registers and freezes the value of 3 different parameters which are stored together with the DTC. The TCM can store up to 7 DTCs. If the number of DTCs exceeds 7, the four first DTCs will always be saved, while the last three are replaced by the latest DTCs stored.

When there is a transmission malfunction registered by the TCM (permanent fault) an emergency program is activated to deal with the fault. The TCM takes corrective action to protect the transmission and maintain as much driveability as possible.
There are different emergency programs depending on the type of malfunction and how serious it is:

- Emergency mode I
- Emergency mode II
- Emergency mode III
- Limp-home mode

Emergency mode I is activated for minor malfunctions and the Limp-home mode for the most serious malfunctions.

For a more detailed description of the emergency programs, see Emergency programs. Emergency Programs In the Event of A Fault

If the malfunction is intermittent the TCM returns to normal operation the next time the ignition is turned on and the indicator and warning lamps stop flashing after the ignition is switched on and off a certain number of times. The ignition may have to be switched on up to five times, depending on the DTC that has been stored.

If a malfunction should for some reason disappear after a DTC has been permanently stored in the TCM, information about the fault remains stored in the TCM.

For each DTC stored a counter records the total number of times the ignition has been switched on without a malfunction since the DTC was stored. When the counter is at 0 the TCM treats the malfunction as a permanent fault. If the counter is greater than 0 the TCM assigns the fault a "no malfunction" status which is the same as an intermittent fault. If the malfunction recurs, the counter is reset to 0.