U0074: Control Module Communication Bus "B" Off

What Does The U0074 Code Mean?

This communication system diagnostic trouble code typically applies to most domestic and import fuel injected engines manufactured since 2004. Those manufacturers include but are not limited to Acura, Buick, Chevrolet, Cadillac, Ford, and Honda.

This code is concerned with the communications circuit between control modules on the vehicle. This communications circuit is most often referred to as Controller Area Network bus communications, or simply put, CAN bus. Without this CAN bus, control modules cannot exchange information, and your scan tool may not be able to communicate with the vehicle, depending on which circuit is affected.

Troubleshooting steps may vary depending upon manufacturer, type of communications system and wire colors and number of wires in the communication system. U0074 refers to the Bus “B” whereas U0073 refers to Bus “A”.

What Are The Symptoms Of The U0074 Code?

Symptoms of a U0074 engine code may include:

• Malfunction Indicator Lamp (MIL) illuminated
• Lack of power
• Poor fuel economy
• All instrument cluster indicator “lights” on
• Possibly a no-crank, no start condition

What Are The Potential Causes Of The U0074 Code?

Potential causes for this code to set are:

• Open in the “B” CAN bus + circuit
• Open in the “B” CAN bus – circuit
• Short to power in either “B” CAN bus circuit
• Short to ground in either “B” CAN bus circuit
• Rarely – faulty control module

How Can You Fix The U0074 Code?

A good starting point is always to check for technical service bulletins (TSB) for your particular vehicle. Your issue may be a known issue with a known fix put out by the manufacturer and can save you time and money during diagnosis.

First, see if you are able to access fault codes and if so, note if there are any other diagnostic fault codes. If any of them are module communication related, diagnose them first. Misdiagnosis has been known to occur if a technician diagnoses this code before any other module communication related system codes have been thoroughly diagnosed.

Next, locate all bus communication connections on your particular vehicle. Once located, visually inspect the connectors and wiring. Look for chafing, rubbing, bare wires, burn spots or melted plastic. Pull the connectors apart and carefully inspect the terminals (the metal parts) inside the connectors. See if they look corroded, burnt or possibly green in color versus the normal metal color you are probably used to seeing.

You can get some Electrical Contact cleaner at any parts store if cleaning of the terminals is needed. If this is not possible, find some 91% rubbing alcohol and a light plastic bristle brush to clean them with. Afterwards let them air dry, get some dielectric silicone compound (same stuff they use for light bulb sockets and spark plug wires) and put some where the terminals come into contact.

If your scan tool can now communicate, or if there were any module communication related fault codes, clear the diagnostic trouble codes from memory, and see if this code returns. If it does not, then the connections were most likely your problem.

If communication is not possible, or you were unable to clear the module communication related fault codes, the only thing left that can be done is to unplug one control module at a time and see if communication with the scan tool occurs or the codes clear. Disconnect the negative battery cable before unplugging the connector at a given control module. Once disconnected, unplug the connector(s) at the control module, hook the battery cable back up and retest. If communication now occurs or the codes now clear, that module / connection is at fault.

If communication is not possible, or you were unable to clear the module communication related fault codes, the only thing left that can be done is to seek assistance from a trained automotive diagnostician.

Recommended Parts

Below are some recommended auto parts to help you address the trouble code affecting your vehicle and get it running smoothly again:

>>> Twippo 372Pcs Waterproof Wire Connectors Kit
>>> INNOVA 5210

Note: During the purchasing process, please check carefully whether the part you want to buy fits your car!

Reference Sources

U0074 Control Module Communication Bus B Off, OBD-Codes.