Communication with the retarder
Check whether the GMS control unit has generated any fault codes. If not: Check the connection between the red CAN bus and the GMS control unit. Check the GMS control unit supply voltage circuit (30) and the GMS control unit activation signal circuit (15). Check the red CAN bus cable harness and connectors. Measure the resistance between the coordinator's pin for CAN-High and CAN-Low of the red CAN bus with the battery disconnected. Resistance should be around 60 ohm. (Due to the two termination resistors connected in parallel.)
What you'll see
No driver-visible symptom recorded.
System reaction
No system-reaction text recorded.
Diagnostic depth
Communication between coordinator and retarder, which is controlled by the GMS control unit, has been interrupted.
The fault may be due to: Fault in the GMS control unit connection to the red CAN bus. Short circuit or open circuit in the GMS control unit supply voltage circuit. Internal fault in the GMS control unit.