U0073
Control Module Communication Bus A Off
If your code reader dashboard displays the generic DTC error code U0073, your vehicle is currently experiencing an active failure related to "Control Module Communication Bus A Off". Proper system troubleshooting is required to safely clear this warning.
Driver's Summary
A U0073 fault code points directly to a problem with control module communication bus a off that the ECM has confirmed over multiple drive cycles. You may notice vehicle shuts off, no start, all dashboard lights on, 'no bus' message, all of which are direct consequences of this malfunction. This is a serious fault — avoid extended driving and have your vehicle inspected by a mechanic as soon as possible to prevent further damage.
Symptoms
Vehicle shuts off, no start, all dashboard lights on, 'no bus' message
Common Causes
- Short in CAN bus wiring
- Water damage to a control module (ABS, TCM, PCM)
- Corroded network connector
- Dead battery
How to Fix
- 1 Test battery and charging system
- 2 Disconnect modules one by one to find the shorted unit
- 3 Repair damaged CAN wiring
- 4 Replace faulty module
Technical Explanation
To set U0073, the PCM samples the affected circuit multiple times per second, comparing live readings against manufacturer-programmed operating windows. A bus-off condition (where the CAN transceiver disables itself due to excessive error frames) is detected when the receiving node counts more than 255 transmission errors — typically caused by a wiring short that creates dominant bit stuffing errors across the network. Once confirmed, the code is stored as a permanent DTC and the MIL is activated. The freeze frame snapshot — recording RPM, load, coolant temperature, and fuel trim at fault detection — is also saved and is critical for accurate diagnosis.
Is It Safe to Drive?
This fault carries real mechanical risk. The root causes — including short in can bus wiring — can trigger a chain reaction of component failures if the vehicle continues to be driven. Have it towed or drive directly to a shop without delay.
Mechanic's Pro Tip
Module replacement should always be the last resort for U0073 after exhaustively verifying all power supply circuits, ground connections, and communication bus wiring. Use a wiring diagram to locate all fuses, relays, and ground points for the affected module, and measure voltage drop on each ground with the circuit loaded. A module "failure" is frequently a corroded ground eyelet or a weak battery causing brownout conditions — fix these first and you'll save hundreds of dollars on an unnecessary module replacement.
Diagnostic testing: $150 - $300; Module replacement: $500 - $1,500+