Diagnostic trouble code (DTC) information

Condition 

Fig 1: Identifying Automatic Transmission Control Module (TCM)

Courtesy of VOLVO CARS OF NORTH AMERICA.

The automatic transmission control module (TCM) receives speed signals from the vehicle speed sensor (VSS) on the transmission. The transmission control module (TCM) uses the signals to select the correct gear. The control module derives and compares the transmission speed with engine speed (RPM) at the transmission. Diagnostic trouble code (DTC) TCM-0020 is stored if the control module registers that transmission vehicle speed signal does not correspond to the transmission speed (RPM).

Substitute Value 

• None.

Possible Source 

• Contact resistance in terminals.
• Open-circuit, short-circuit to ground, short-circuit to supply voltage in power supply.
• Open-circuit, short-circuit to ground, short-circuit to supply voltage in signal cable.
• Defective vehicle speed sensor (VSS).

Fault symptom[s] 

• General orange warning lamp lit.
• Malfunction indicator lamp (MIL) lit.
• No lock-up function.
• Harsh gear shifting.

HINT: Harsh gear shifting can be caused by: 

• No adaptation of the gear slippage times at high altitude (High Altitude Compensation).
• No reduction of line pressure when shifting.
• No reduction of line pressure when moving the gear selector between positions P-R, N-R and N-D.
• No torque limiting request to engine control module (ECM) when shifting.