OBD-II trouble code
U0073: Control Module Communication Bus A Off
A control module has counted so many communication errors that it shut itself off the CAN bus to protect the network — the 'bus off' state. Almost always a wiring short or a failed module transceiver.
Quick facts
- System
- Network
- Category
- Network Communication
- Severity
- High severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $100 – $1,200
- DIY difficulty
- Shop recommended
What does U0073 mean?
U0073 means a control module has entered the CAN 'bus off' state on communication bus A. CAN modules keep two internal error counters, and when a module accumulates too many transmit errors, the protocol forces it to disconnect itself from the bus entirely as a self-protection measure. This prevents one malfunctioning node from flooding the network with errors and taking everyone down with it. U0073 is the code that records that a module had to take itself offline.
Reaching the bus off state takes a serious, repeated fault — not occasional noise. The most common triggers are a hard short on the CAN wiring (CAN-High or CAN-Low shorted to power, to ground, or to each other), a complete open in the bus, a failed terminating resistor, or a module whose CAN transceiver has failed and can no longer transmit valid frames. Unlike a soft performance fault, bus off is a definitive event: the module gave up after the error count crossed its limit.
The symptoms are usually severe because a module dropping fully off the bus takes its functions with it. Depending on which module went bus off and which bus is affected, you can see a no-start, no shifting, dead gauges, or a cascade of warning lights as other modules lose the data they expected. U0073 is a tow-it-in code in most cases — diagnosis centers on finding the wiring short or the failed module that drove the error counter to its limit.
Common causes
- CAN-High or CAN-Low shorted to power or ground
- CAN-High and CAN-Low shorted together
- Complete open (break) in a CAN bus wire
- Failed CAN transceiver inside a control module
- Both terminating resistors lost, collapsing the bus
- Severe connector corrosion or water intrusion on the bus
- Damaged harness from rodent activity, accident, or chafing
- A defective module continuously transmitting errors before going offline
Symptoms
- One or more systems completely non-functional (no-start, no shift, dead cluster)
- Multiple warning lights illuminated at once
- Scan tool cannot communicate with the affected module at all
- Gauges dead or frozen
- Transmission in limp mode or fully disabled
- Loss of comfort and convenience features tied to the affected bus
- Bus off / lost-communication U-codes stored in several modules
Diagnostic steps
- 1.Scan every module and note which report communication faults; identify which bus (A) and which module went bus off.
- 2.With the battery disconnected, measure resistance across CAN-High and CAN-Low. About 60 ohms is healthy; near 0 indicates a short, infinite indicates an open, ~120 ohms means a lost terminator or branch.
- 3.Inspect the bus wiring end to end for shorts to power/ground, breaks, chafing, and rodent damage.
- 4.Check connectors and splice packs for corrosion, water intrusion, and backed-out terminals.
- 5.Key on, measure CAN-High and CAN-Low voltages (rest near 2.5 volts) to confirm the bus is balanced.
- 6.If wiring checks out, disconnect modules one at a time to identify a module with a failed transceiver that is driving the bus off.
Repair cost
$100 – $1,200
Diagnosis typically runs $150-$300. A wiring short or open repair lands at $150-$600 depending on where the damage is and how hard it is to reach. A failed terminator or connector repair is on the lower end. Replacing a module with a failed transceiver, including programming, runs $400-$1,000. European and luxury vehicles with multiple buses tend toward the upper range.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with module communication / can bus diagnosis preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
Leave this one to a qualified shop. It typically involves emissions-critical components, refrigerant handling, or other work that requires manufacturer-grade tooling, training, or certification. DIY attempts often produce a more expensive problem than the original code.