Running a modern car demands that a large number of modules and sensors communicate in real time. The sensors and modules send information through the controller area network (CAN) bus to the powertrain control module (PCM). If you notice strange symptoms, like engine trouble, and the locking system not working, the problem can be in the communication. Grab an OBD-II sensor and scan the car. In case you get a U0073 code you need to know what you are dealing with.
The U0073 code is defined as a “Control module communication bus A off”. That means that the CAN bus controller has detected a problem with a cable that is used for communication between several modules. That can impact problems and erratic behavior of several systems in the vehicle. The possible causes for this error are the damaged wiring harness of the CAN bus controller, faulty electronic control module, or connection issues.
The U0073, like the other communication errors, is very serious. It can cause unpredictable problems that can impact the safety of the car and the driver. If you detect it, refrain from driving the vehicle. You can try to diagnose and fix the issue yourself or contact the mechanic for a professional approach.
Understanding the U0073 Code: A Quick Snapshot
We are often not aware, but there are numerous electrical components in our car, like sensors and modules. They are constantly gathering and sending information. They are ensuring that every part and system of the vehicle is working properly.
To send and receive that information, the car uses the controller area network (CAN) bus. The CAN bus sends this information to the PCM and ECM where they are processed. For communication, the CAN bus uses two wires, A and B. There is a voltage difference in these wires. That way the CAN bus knows how to send and receive information.
Depending on the manufacturer and the model, the A or B wires can be used for either sending or receiving information. With proper information and good diagnostics, you won’t lose much time in finding the culprit.
What Exactly is the U0073 Code?
To use the simple terms a U0073 code is a signal that the modules are not sending or receiving information through the CAM network. When that happens, the engine, transmission, and other major car systems cannot adjust to the situation.
The Role of Control Module Communication Bus ‘A’ in Your Vehicle
There are two communication buses in the car, called high and low CAN. One is used to send information to the PCM and the ECM, and the other is to receive information. Depending on the vehicle made, the buses can have different purposes. So, bus A will not always send information, and so the bus B will not always deliver it.
These buses have different voltage readouts, so detecting which bus is which is easy. The low CAN bus readout is between 1.5 and 2.5 volts, while a high CAN bus readout is between 2.5 and 3.5 volts.
This CAN design allowed many different elements to communicate with each other. This also lowered the need for excess wiring. These features thus allowed the installation of additional systems in the car without overloading the modules.
Spotting the Signs: Symptoms of the U0073 Code
The U0073 code is a communication code and it comes with a variety of symptoms. Since there is a problem in sending and receiving information, that can lead to an erratic behavior of some components. Also, the engine will have trouble functioning. But, if these symptoms come together then you can guess that the U0073 code is the issue:
- Turned on the check engine light. Once the ECU gets the information about the lack of communication it will trigger a check engine light
- Gauges on the instrument panel may start showing erratic information. Since the modules are not communicating properly, the dashboard may receive conflicting information
- Problems with starting the engine. Depending on the module that is also afflicted by the error code, you can end up with a no-start condition
- Decrease in engine performance. You may notice the lack of acceleration. Because of the U0073 code’s wide array of underlying issues, it can also affect performance.
- Increased fuel consumption. Some sensors monitor the air-to-fuel ratio. They are responsible for adding the right amount of fuel to the mix. If they are affected by this error you will notice a rise in fuel consumption
- Strange door lock behavior. The doors can lock and unlock all of a sudden without your part in doing so
- The transmission is stuck in a gear. Most often, the transmission won’t move from the second gear.
Uncommon Vehicle Behavior to Watch Out For
Depending on the communication problem you may experience strange behavior from different car systems. The most common that we listed is erratic door lock sensor behavior. But other electrical systems can also act in the same way. Watch out for anything that is out of the ordinary.
Diagnostic Warning Lights and What They Mean
Like with most error codes once the ECU triggers them, it will trigger a check engine light too. In some situations, if the error is specific, it is followed with the oil pressure light or an ESP or ABS light. But, when the problem is too wide to narrow it with a specific error light, the check engine light will warn you of the problem.
The check engine light is there to notify you that there is a problem that requires your attention. To further diagnose the problem you will need a code reader.
The Possible Causes of the U0073 Code
Common Factors That Can Trigger the U0073 Code
- Bad battery
- Communication problem with the module on the CAN bus A
- Problem with wiring on the CAN bus A
- Faulty ECU.
Technical Glitches That Lead to the U0073 Code
The communication issues are usually triggered by the wiring problems. A short circuit or a bad ground wire can lead to several strange symptoms. The wiring problem can be anywhere on the CAN bus A. That includes the modules and the communication bus itself.
Another glitch that can cause the U0073 code is a low power voltage supply from the battery. The battery in ideal condition provides 12.5 or 12.6 volts of current. If it is lower then the modules and sensors will not work properly.
Risk of Ignoring the U0073 Code
Impact on Vehicle Performance
There are several modules and sensors that have an impact on the vehicle’s performance. Some of them are on the CAM bus A. If they are affected by the communication problem then the result can be a combustion issue. Sometimes there is a problem with the transmission.
If the combustion process is affected by this error then the car will consume more fuel, and will also have lower performance. It will not accelerate properly, and in some cases, you can press the pedal to the maximum with little or no effect.
If the transmission control module is plagued with this error, then gear shifting will be compromised. Usually, the car will not shift further from second gear. That will also raise the fuel consumption and can damage the engine.
But, if the symptoms are minor, like powered windows issues, and are not increasing that is a sign that there are no major issues. But, that doesn’t mean that the problem will not further develop. Even if the symptoms are minor, we advise diagnostics and fixing of the problem as soon as possible.
Long-Term Consequences of Neglecting the U0073 Code
The U0073 error code won’t go away without a proper fix. If you continue driving with this error the communication issues can develop even further. The two most important systems in every vehicle can be affected by this error – the engine and the transmission.
When this error is neglected the error can result in no-start situations. You can end up in the middle of nowhere with a car that cannot turn on. If the transmission is not functioning properly, the problem will only increase. If the car is constantly in the high RPMs that is not good, both for the engine and for the transmission.
The DIY Guide: How to Troubleshoot the U0073 Code
Step-by-Step Guide to Diagnose the U0073 Code
The U0073 error code can lead you in several different directions. If it is not diagnosed properly can cost you a lot more than it should. The best way to avoid the situation of spending hard-earned dollars with the problem still there is to follow this diagnostics process:
- Check the car with the error code reader. Connect the OBD-II code reader to the car’s computer. Scan the computer for errors. This way you will shorten diagnosis time. If there are other errors besides the U0073 identify them. Usually, the code is referred to as a communication fault with another module or a sensor. You can also erase the error codes and do a test drive. If the scanner has a freeze frame option, you can use it to identify the moment when the error shows up. You can also see what parameters led to the error
- Test the problematic modules. Those include all the modules on the CAN bus A. If there is an error code that shows a problem with a module or a sensor use the multimeter to test it. Check the continuity, and if the ground wire is good. Also, do a checkup of the connectors and the overall state of the wiring
- Inspect the condition of the battery. A worn or damaged battery is often the culprit for all communication codes. If the battery is not providing enough power, then the modules and sensors will not work as they should. When checking the condition of the battery, also inspect the battery cables for any obvious issues or a loose connection. Check for any corrosion on the battery terminals. If you notice green or blue buildup then you are dealing with a sulfated battery, and you will need to replace it
- Do a visual check of the CAN bus area. There are a lot of wirings and connectors. If you notice burned wire insulation or corroded or loose connections, they can cause a communication issue
- Obtain and check the technical service bulletin (TSB) for your vehicle. The manufacturer may already assess the problem you are dealing with, and in the TSB they are offering the solution. That way you can save a lot of time and money on diagnostics and replacement parts.
Tools Needed to Fix the U0073 Code
Like with all communication errors if you want to diagnose and fix the error you will need a good scan tool and a multimeter. The scan tool is needed to check the ECU for error codes. The multimeter is essential for testing and diagnosing problems with any electrical circuit, including the sensors and modules.
Precautions While Troubleshooting
Since you are dealing with electricity you should be extra careful. That means avoiding touching exposed wiring. You should also use safety goggles and gloves to narrow down the possibility of an injury.
Check Out 3 Easy Steps On How To Fix U0073 Code:
When to Consult a Professional for the U0073 Code
If you cannot detect or resolve the issue yourself, then you should turn to the help of a professional. A mechanic knows the ins and outs of every system in the car. He knows the best way to locate, reach, and diagnose every sensor in the car.
Scenarios That Call for Expert Assistance
If the problem persists and you cannot find the underlying issue, then the expert help will speed things up. Some of the most common scenarios are:
- You checked most of the modules, but you cannot find a problem in communication
- After checking the electronics system you concluded that the problem is in the ECU but it is too difficult task for you to resolve it
- There is a problem with the wiring harness, and you don’t want to deal with it. Replacing a wiring harness can be a difficult task due to problems with accessibility and location.
Choosing the Right Mechanic for Your U0073 Code Troubles
When choosing a mechanic you should look for one with car electric experience. Solving problems with electronic communication between modules is not something that every mechanic knows to do. It demands general knowledge about communication in the vehicle, diagnosing and testing, and pinpointing the real issue.
Some mechanics start replacing parts which is the common cause of this issue, without proper diagnosis. That way they are wasting your money and time, and you still end up with a car with the same problem.
FAQs about the U0073 Code
What Is the Code for a Malfunctioning Transmission Control Module?
Since the transmission control module is a complex system, several error codes are associated. If you have detected any of these errors you should know that the TCM is in trouble:
- P0700 – transmission control module malfunction. This is a generic code that points to a problem with the TCM. The underlying cause for this error can be the connectors and wiring of the TCM, a faulty TCM itself, or damaged input and output transmission sensors
- P0706 – Transmission range sensor circuit range. This error is frequently a result of starting the vehicle while it is in gear. That can cause erratic shifting, or even inability to start the car. The usual suspects for this TCM error code are a damaged shift linkage, a faulty neutral switch, or a TCM wiring problem
- P0613 – Transmission Control Module System Fault. This error is a result of a problem with the internal control processor. The root causes for this error are either a poor electrical connection and wiring or a failing TCM.
You can test the TCM with only the multimeter, and see what is the real cause for the problems.
What Are the Signs of a Defective Fuel Composition Sensor?
The fuel composition sensor monitors the fuel composition and triggers a problem if there is an abnormal amount of non-gasoline composition in the fuel. If there is a problem with this sensor it is followed with P0178 and P0179 error codes. The common symptoms of these problems are increased fuel consumption, low engine performance, and having a hard time starting the engine.
Will a Bad Fuel Pump Cause a Code?
No, the bad fuel pump will not cause a U0073. But, if after scanning the car with an OBD-II scanner you also get a U0109 code, that means that the CAN has lost the communication with the fuel pump relay. That can point to a problem with a fuel pump.
How Can You Tell If Your Control Module Is Faulty?
The ECM is the heart of the car’s electrical system, and if it goes bad it will be followed with several symptoms. The most common issues are
- Check engine light is on
- Poor engine performance
- Poor fuel economy
- Increase in bad emission
- Problems with stalling.
There are a couple of ways to diagnose a bad ECM:
- Check it with the OBD-II scanner. Error codes P0700, P0602, P0600, and P0606 indicates a possible issue with the ECM
- Do a visual inspection. Check if the ECU emitting a burnt smell. Next, check the pins on the connectors. Finally, open the ECU board and look for any damaged components, or corrosion on the board
- Swap with another ECU. When you are not sure if the ECU is working okay, swap it for the ECU that fits your car. If it is working properly, then the ECU is the issue. This method helps only with cars made before 1996 because then the ECU didn’t require programming
- Check the battery. Inspect the overall state of the battery, and check the wiring and terminals for damage or rust. Test it with the multimeter. The proper voltage for the regular acid battery is 12.5 or 12.6 volts.
How Can I Tell If My CAN Bus Is Working?
The best way to check if the CAN bus working properly is to test it. There are two CAN lines, CAN low and CAN high and you need to test them both. This test includes testing resistance (ohms) between the two lines. For this testing, you will need a multimeter and a CAN electrical diagram.
- Disconnect the battery. This is done because the resistance measures are not correct with the connected battery
- With the help of a diagram locate the CAN point that is easy to access. Much of the wiring is behind the dashboard, and your goal is to make your job as easy as possible. You don’t want to end up disassembling half of the car
- Do not disconnect any connections. Measure the resistance between CAN high and CAN low lines. The readout should be 60 ohms. Anything lower than 57 and higher than 62 ohms is a potential issue
- Find one of the CAN terminal resistances in the diagram and disconnect the unit that contains it. Check the internal resistance by testing the pins on the CAN connector. The value of the multimeter needs to be about 120 ohms. If it is below 117 and above 123 ohms then you found a possible problem.
Need More Help with a U0073 Code?
Communication codes can have very different symptoms. Sometimes the issue is benign, and the driver doesn’t resolve the problem. In other, the whole car is confused and working out of synch. In both situations, the problem needs to be addressed as soon as possible. Problems from the first group can grow, and those in the second group are already a potential hazard.
If you cannot resolve these issues alone, contact a professional. Ask around for a mechanic who deals with electronic issues, and contact him. Let him check the whole system and find the underlying issue. That way you will spend some money, but will save a lot of nerves. Do not forget, this problem can be a safety issue, so by fixing it, you are keeping yourself, and others safe.
