800B CDR23: Diagnosis/troubleshooting

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DIAGNOSIS/TROUBLESHOOTING - 800B CDR23

Work instruction			Display OK	If not OK
1	Check CAN bus leads, CAN-high and CAN-low for short circuit	Switch off ignition Remove plug A from the instrument cluster Pull plug off the Tiptronic control unit Pull plug off the PSM control unit Pull off steering angle sensor plug Pull plug off the DME control unit Measure resistance on plug A of the instrument cluster between pin 15 and pin 31 Measure resistance between pin 3 and pin 4 on the plug on the DME control unit	Step 2	Repair wiring harness -> End
2	Check CAN bus lead, CAN-high for short to ground	Measure resistance between plug A on instrument cluster pin 15 and ground Measure resistance between pin 3 and ground on the plug B of the DME control unit	Step 3	Repair wiring harness -> End
3	Check CAN bus lead, CAN-low for short to B+	Switch on ignition Measure resistance between plug A on instrument cluster pin 31 and ground Measure voltage between pin 3 and ground on the plug B on the DME control unit	0 V Step 4	Repair wiring harness -> End
4	Determine faulty control unit	Switch off ignition Reconnect all plugs to control units Pull off plugs to the control units (except instrument cluster) individually and read out the fault memory of the instrument cluster and check whether the fault has been remedied	The fault is remedied by disconnecting the plug connection of a control unit. Step 5	The fault is still present Step 6
5	Replace the control unit which was last disconnected from the CAN bus		-> End
6	Replace instrument cluster		-> End