Fault codes cannot be read out for the following faults (these faults must be rectified beforehand):
– If the display on the HHT remains dark:
First check fuse terminal 30 and ground connection of diagnostic socket, then check on other vehicle whether the Multiplexer is in order.
– If "Switch on ignition" is shown in the HHT display when the ignition is switched on:
Check fuse terminal 15 of diagnostic socket.
– If "System is not contacted or open-circuit in diagnostic line" is shown in the HHT display:
Check fuse F4 on fuse carrier A3.
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– If the TCC is not recognized after several short tests, the diagnostic line (to pin 18 on TCC control module) may be open-circuited or the control module (TCC and retarder control module separately) does not yet have diagnostic capability.
– for fault text shown in the HHT display:
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TCC
Diagnostic socket contact
XX
System does not respond
Possible cause:
– Diagnostic line
– Control module
voltage supply
– Control module
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Short test/system selection
Commercial vehicle
Actual values cannot be read out:
– If the display on the HHT remains dark:
First check fuse terminal 30 and ground connection of diagnostic socket, then check on other vehicle whether the Multiplexer is in order.
– If "Switch on ignition" is shown in the HHT display when the ignition is switched on:
Check fuse terminal 15 of diagnostic socket.
– If "System is not contacted or open-circuit in diagnostic line" is shown in the HHT display:
Check fuse F4 on fuse carrier A3. If the fuse blows again when the ignition is switched on, see remedy below.
– If the TCC is not recognized after several short tests, the diagnostic line (to pin 18 on TCC control module) may be open-circuited or the control module (TCC and retarder control module separately) does not yet have diagnostic capability.
– for fault text shown in the HHT display:
Remedy if the fuse F4-A3 blows immediately when the ignition is switched on.
1. Switch off ignition and replace fuse F4-A3.
2. Disconnect TCC control module and switch on ignition:
- If fuse F4-A3 blows again, check wiring (voltage supply) to control module and wiring to relay carrier A35 and if necessary check A31-K5 for short-circuit to ground.
- If fuse does not blow, replace TCC control module on an experimental basis.
Diagnostic socket contact
XX
System does not respond
Possible cause:
– Diagnostic line
– Control module
voltage supply
– Control module
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TCC
Short test/system selection
Commercial vehicle