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U0073 — Control Module Communication Bus Off

Generic OBD-II · all makesNetwork / communication

U0073 indicates that a control module on the vehicle's Controller Area Network (CAN) bus has detected a bus-off condition, meaning it has lost communication with other modules. This is typically caused by a wiring fault, a defective module, or a short in the network, not the engine computer itself.

Symptoms

What causes it — most likely first

1. CAN bus wiring fault

Short circuit, open circuit, or high resistance in the twisted-pair CAN wires (CAN-H and CAN-L) is the most common cause. This can occur at connectors, chafed wires, or damaged harnesses.

2. Faulty control module (other than PCM/ECM)

A defective module (e.g., ABS, BCM, TCM) can pull the bus voltage low or generate excessive noise, causing a bus-off condition. This is more likely than a PCM failure.

3. Missing or incorrect termination resistor

The CAN bus requires 120-ohm termination resistors at each end. A missing, open, or shorted resistor can disrupt communication and trigger U0073.

4. Corroded or loose connector pins

Oxidation or poor pin contact at module connectors or splice points can intermittently break the bus, especially in high-humidity or salt-belt vehicles.

5. Aftermarket accessory interference

Improperly installed aftermarket electronics (e.g., remote start, alarm, stereo) can tap into the CAN bus incorrectly, causing a short or data corruption.

6. PCM/ECM internal failure

Rare but possible; the PCM itself can fail and go bus-off. This is the least likely cause and should only be considered after all wiring and other modules are verified.

How it's diagnosed

  1. Check for other stored codes (e.g., U0100-U0300) to identify which module(s) lost communication.
  2. Visually inspect the CAN bus wiring and connectors for damage, corrosion, or loose pins, especially near areas prone to rubbing or moisture.
  3. Measure resistance between CAN-H and CAN-L at the diagnostic connector (DLC) with the battery disconnected; should be approximately 60 ohms (two 120-ohm resistors in parallel).
  4. If resistance is 120 ohms, one termination resistor is missing; if 0 ohms, there is a short. Use a multimeter and oscilloscope to isolate the fault.
  5. Disconnect modules one at a time while monitoring bus voltage or resistance to identify which module causes the bus to return to normal.
  6. If all wiring and modules check out, test the PCM/ECM by swapping with a known-good unit (if possible) or performing a manufacturer-specific bus-off recovery procedure.

Code facts & related codes

SystemNetwork / communication
StandardizationSAE generic — identical on every make
Related codesU0070 — Vehicle Communication Bus E LowU0071 — Vehicle Communication Bus E HighU0072 — Vehicle Communication Bus E Shorted U0074 — Control Module Communication Bus B OffU0075 — Control Module Communication Bus C OffU0076 — Control Module Communication Bus D Off

Frequently asked

Do I need to replace the PCM for code U0073?

Almost never. The PCM is rarely the cause of a bus-off code. Most U0073 cases are due to wiring faults, a bad connector, or a different module failing. Replacing the PCM without proper diagnosis is a common and costly mistake.

Can a dead battery cause U0073?

Yes, a severely discharged or failing battery can cause low voltage on the CAN bus, leading to communication errors. Always check battery voltage and charging system before diving into wiring repairs.

Will clearing the code fix the problem?

Clearing the code may temporarily turn off the check engine light, but if the underlying fault (e.g., a shorted wire) remains, the code will return. Diagnosis is required to find and fix the root cause.

Is it safe to drive with U0073?

It depends. If the bus-off affects critical systems like the engine or transmission control, the vehicle may stall or not shift properly. If only comfort modules are affected, driving may be possible but with reduced functionality. Have the issue diagnosed promptly.