Fault code U0073 – a step-by-step guide to diagnosing and fixing it

Error code U0073 is displayed and the check engine light is on - what does this mean?

The DTC U0073 is a communication error that occurs when the Control Module Communication Bus "A" Off detects a fault in the network between the control units. The OBD system registers this fault code if communication between various electronic control units via the CAN bus is interrupted or disrupted.

What causes can this fault code have?

• Defective gateway module or body control module (BCM)
• Damaged CAN bus cabling between the control units
• Corroded or loose plug connections on the CAN bus
• Short circuit in the bus cabling
• Defective fuses in the affected control units
• Faulty earth connections of the electronic modules
• Voltage fluctuations in the vehicle electrical system
• Defective control units blocking the bus

What symptoms occur in parallel with fault code U0073?

• Starting problems: The vehicle may not start or may exhibit delayed starting behavior. Instrument failure: Various displays in the dashboard do not function properly or fail completely. Electronics fault: Air conditioning, radio, navigation system or other electronic systems are malfunctioning. Warning lights: Multiple indicator lights may illuminate simultaneously. Loss of communication: Diagnostic devices cannot communicate with all control units.

How can the problem with fault code U0073 be rectified?

• Correcting trouble code U0073 requires a systematic diagnosis of the CAN bus communication.
• Checking all fuses of the affected control units and replacing defective fuses
• Checking the CAN bus cabling for damage, breaks or short circuits with subsequent repair
• Cleaning and securing all CAN bus plug connections, especially in areas at risk of moisture
• Measuring the CAN bus voltage and resistance values to identify defective cables
• Replacement of the gateway module or body control module if a defect is detected
• Checking and repairing the earth connections of all electronic modules involved
• Isolation of defective control units by gradually disconnecting the bus participants to isolate the fault