Diagnostic Functions: Overview

Overview

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 transmission control module (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 Automatic Transmission. When a diagnostic trouble code (DTC) is stored the system registers and freezes the value of 3 different parameters which are stored together with the diagnostic trouble code (DTC). The transmission control module (TCM) can store up to 7 diagnostic trouble codes (DTCs). If the number of diagnostic trouble codes (DTCs) exceeds 7, the four first DTCs will always be saved, while the last three are replaced by the latest diagnostic trouble codes (DTCs) stored.
When there is a transmission malfunction registered by the transmission control module (TCM) (permanent fault) an emergency program is activated to deal with the fault. The transmission control module (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 transmission control module (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 diagnostic trouble code (DTC) that has been stored.
If a malfunction should for some reason disappear after a diagnostic trouble code (DTC) has been permanently stored in the transmission control module (TCM), information about the fault remains stored in the transmission control module (TCM).
For each diagnostic trouble code (DTC) stored a counter records the total number of times the ignition has been switched on without a malfunction since the diagnostic trouble code (DTC) was stored. When the counter is at 0 the transmission control module (TCM) treats the malfunction as a permanent fault. If the counter is greater than 0 the transmission control module (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.

On Board Diagnostics II (OBD II)
In some markets where an on-board diagnostics system II (OBD II) is a statutory requirement the transmission control module (TCM) can also activate the Malfunction Indicator Lamp (MIL) in the combined instrument panel. The malfunction indicator lamp (MIL) is controlled by the engine control module (ECM). A transmission malfunction that affects exhaust emissions will cause a diagnostic trouble code (DTC) to be posted and the transmission control module (TCM) sends a request to the engine control module (ECM) to activate the malfunction indicator lamp (MIL). The request to activate the malfunction indicator lamp (MIL) is maintained while the diagnostic trouble code (DTC), whether the fault is permanent or intermittent. This situation applies to the certain transmission diagnostic trouble codes (DTCs). See also On Board Diagnostics II (OBD II) On Board Diagnostics II (OBD II).
Engine Control Module (ECM) Motronic 4.4 posts a diagnostic trouble code (DTC) when the transmission sends a request for the malfunction indicator lamp (MIL).