|Trouble Code||Fault Location||Probable Cause|
|U0001||Controller area network (CAN) data bus: high speed bus/communication control module|
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What Does Code U0001 Mean?
This code is concerned with the communications circuit between control modules throughout 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 in some cases, your scan tool may not be able to communicate with the vehicle, depending on which of these CAN circuits is affected.
For this particular code, the communication circuit we will be working with is CAN C, which may also be referred to as under-hood or under-vehicle CAN bus, as the modules that typically communicate on this network can be found under-hood or under-car.
What is causing this code to set is one main module has the task of communicating with other modules on CAN C to make sure they all report in. This “main module” could be the Body Computer or a Central Gateway Module, depending on the vehicle. For this particular code to set, most often the Anti-Lock Brake (ABS) Controller at some point in time did not “check in”. Usually this code will set only as a history / memory code. If it is active or present right now, then you probably will not be able to access ABS codes or data.
This code is possible to be set for other modules on CAN C bus, depending upon the vehicle manufacturer.
What are the common causes of code U0001?
- Open in the power supply to the module that set the code
- Open in the ground supply to the module that set the code
- Open in the CAN bus + circuit
- Open in the CAN bus – circuit
- Short to ground on either CAN C bus circuit
- Faulty module – rarely
What are the symptoms of code U0001?
- Malfunction Indicator Light (MIL) “On”
- All engine related indicators (lights) “on” in the instrument cluster
- All engine related gauges inoperative in the instrument cluster
- Functions related to the non-communicating module inoperative
How do you troubleshoot code U0001?
Before opening the hood or popping body panels a good practice to get into is to always check for technical service bulletins (TSB) for your particular vehicle. The vehicle manufacturer may have a known issue for the particular problem you are dealing with on your vehicle and it pays to check it out before you head down the wrong path.
Next, see if you are able to access fault codes.
If your scan tool can access fault codes and the only one you retrieve from other modules is the U0001, then the U0001 code is either intermittent or a memory code. The only way to access this code is to do so as a history code. If the code is current, chances are you would not be able to access codes for any of the modules on CAN C bus. (depends on the vehicle)
The most common failure is loss of power or ground.
Check all fuses that power up the module that the other modules were unable to communicate with. Check all grounds for that module too. Locate where the ground attaching points are on the vehicle and make sure that these connections are clean and tight. If you have to, take them loose, get a small wire bristle brush and baking soda/water solution and clean each one, both the connector and where it contacts.
After checking powers and grounds, if any repairs were made, clear the diagnostic trouble codes from memory, and see if the U0001 code returns or communication with all modules has been re-established. If the code does not return or communication is re-established, then the fuses/connections were most likely your problem.
Next, locate the CAN C bus communication connections on your particular vehicle, and most importantly the connector at the module that was having the communications issue. Disconnect the negative battery cable before unplugging the connector at a given control module. 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 or burnt. 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 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 the U0001 code continues to return or communication is still not possible, the only thing left that can be done is to seek assistance from a trained automotive diagnostician.