What Does Engine Code U0073 Mean?

Engine code U0073 means that one of the wires connecting your car’s controller area network bus is not communicating with the other modules.
Written by Brittni Brinn
Reviewed by Melanie Reiff
Jan 19, 2022
If your car is showing a U0073 engine code, it means that communication between your vehicle’s modules has been lost. The modules send information about your car’s performance through the controller area network (CAN) bus to the powertrain control module (PCM), where the data is used to make adjustments to the engine.
Diagnostic Trouble Codes (DTC) are how your car communicates the nature of a problem or malfunction. You (or your mechanic) can view the DTCs by using an OBD-II code reader. Once you know the meaning of a DTC, you can evaluate the problem and decide on the best course of action.
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What does the engine code U0073 mean?

Definition: Control module communication bus ‘A’ off
There are many module devices located throughout your vehicle. These modules send information about your car’s performance through the CAN bus to the PCM. The PCM then uses the data to make adjustments to your engine’s fuel intake.
The CAN bus communicates with the modules in your car using two wires: CAN high and CAN low. The difference in voltage between the two wires is how the CAN bus receives and sends information. Depending on the make of vehicle you drive, ‘A’ may refer to either the CAN high or CAN low wire.

How much will it cost to fix?

The cost to fix a U0073 engine code varies depending on the nature of the problem, your make of vehicle, and your location. Diagnosing the cause will take a mechanic around one hour. Labor costs for car repair shops range from $75 to $150 an hour.

What can cause the U0073 engine code?

A U0073 engine code indicates there is a problem with the CAN bus unit. The ‘A’ circuit is one of two wires that gathers information from the car’s modules. If your car records a U0073 engine code, it may be caused by the following problems:
  • The ‘A’ circuit may be disconnected or shorted
  • Other wiring or connection problems with CAN bus
  • The module harness is open or shorted
  • Faulty control module

Common symptoms of the U0073 engine code

If your car shows a U0073 engine code, you may see these common symptoms: 
In some cases, this problem may also prevent your car from starting. Depending on which modules are unable to send information to the CAN bus, everything from your dashboard indicators to your car’s transmission may be affected.
Key Takeaway When your car loses communication with the modules monitoring your vehicle’s performance, it affects your fuel economy and may even stop your car from starting.

How serious is the U0073 engine code?

The U0073 engine code is very serious and should be repaired as soon as possible. Because all of the data needed to keep the engine running smoothly goes through the CAN bus, a break in communication can be disastrous. 
If left unchecked, your car’s fuel economy will plummet and you may have trouble starting and running your car.

Can I fix the U0073 engine code myself?

Fixing a U0073 engine code is a challenging process. Because the U0073 engine code covers a range of problems that result from a communication loss with the CAN bus, the cause must be correctly diagnosed before starting repairs. To be safe, it’s best to leave the diagnosis to the professionals.
There are steps you can take to rule out some of the problems that may be triggering a U0073 code:
  • Check your battery—low power can cause a U0073 code
  • If you have a UCB II code reader, see if there are other DTCs logged—they may indicate if other problems are causing the U0073 code
  • Do a visual inspection of the CAN bus area—if you see broken wires or loose connections, they may be the cause of the U0073 code
  • Look for technical service bulletins (TSBs) put out by your car’s manufacturer
If you’re comfortable doing more complicated tests on your vehicle, check each module to see if there is a communication issue or failure. It may be that one of your modules needs to be replaced.

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