U0074
UNetworkControl Module Communication Bus B Off
What does this code mean?
Severity : HighU0074 means communication bus B (often a secondary CAN network) has gone into a bus off state: a control module stopped communicating on it after too many errors. Modules connected to this bus can no longer share data, which often triggers several other faults at the same time.
Symptoms
- Check engine light or several warning lights on the dashboard.
- Multiple U codes for lost communication stored at once.
- Features controlled by bus B modules not working or erratic.
- Hard start or no start depending on the modules involved.
- Possible limp mode on the engine or transmission.
Possible causes
- Bus B CAN wire broken, shorted or with damaged insulation.
- Corroded or loose connector on a module on the network.
- Faulty control module disrupting the bus.
- Missing or out-of-spec bus terminating resistor.
- Low battery voltage or poor ground connection.
- Aftermarket electrical accessory interfering with the network.
Diagnosis and repair
- Check battery condition, charging voltage and main grounds.
- Read all stored codes to identify which modules are silent.
- Measure resistance between CAN High and CAN Low with ignition off (about 60 ohms expected).
- Unplug modules one at a time to find the one pulling the bus down.
- Repair the wiring or replace the faulty module, then clear codes and retest.
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Code
U0074
Category
Network
Prefix
U
Standard
OBD-II / SAE J2012