|Code||Fault Location||Probable Cause|
|U0073|| Control module - data bus Off |
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Table of Contents
- What Does Code U0073 Mean?
- What are the common causes of code U0073?
- What are the symptoms of code U0073?
- How do you troubleshoot code U0073?
- Codes Related to U0073
- Get Help with U0073
What Does Code U0073 Mean?Vehicles are controlled by electronic means in some fashion or another. Whether actively controlled with a button or switch or passively controlled by a module, electrical systems are operated based on the input supplied to them and their output response. In turn, modules communicate those parameters with each other so all systems operate seamlessly. Communication is done via a data bus network, often referred to as a Controller Area Network (CANbus). The communication is crucial to ensure body, engine, transmission, anti-lock brakes, and all other systems are able to safely work together. When communication breaks down intermittently or fully between modules, a code is set in a module to indicate the failure. The code, U0073, can register in one or more modules: powertrain control module (PCM), transmission control module (TCM), anti-lock brake (ABS) module, or body control module (BCM) in various locations. Typically, the code sets in the module that experienced a loss of communication.
What are the common causes of code U0073?
- The terminal pins have backed out at the module connector.
- A module's electrical connector is not fully seated.
- The CANbus are open or shorted to ground.
- Corrosion in various control module connectors.
- Intermittent or poor connections in the circuit connectors.
- The data link resistor is open or shorted.
- Water in various control module connectors.
- Shorted control module.
What are the symptoms of code U0073?
- The Check Engine light may be on.
- Instrument panel cluster warning lamps may illuminate.
- The transmission may not shift or defaults to 2nd gear.
- The door locks may cycle by themselves.
- The engine may not crank intermittently.
- A driver information center (DIC) message is displayed.
- The cluster gauges may operate erratically.
- Applying the brakes may cause the cluster to function erratically unwarranted chimes to sound.
How do you troubleshoot code U0073?Because DTC U0073 is used in multiple modules, it can be difficult and time-consuming to find its root cause. The code indicates an error in communication, but symptoms that occur may seem unrelated. For example, a communication error at the instrument panel can cause the transmission to get stuck in limp-in mode. To diagnose DTC U0073, a good-quality digital volt-ohmeter (DVOM) is needed. You'll also require detailed wiring diagrams for your specific vehicle for all modules on the CANbus system, which you can request at many auto parts stores. Image courtesy of General Motors Check for DLC communication Plug a scan tool into the data link connector port under the dash and attempt to read the codes. The scan tool should power up when plugged in. If it does not, check the fuse for the DLC and re-test. If DTC U0073 is present, check which codes, if any, are also present. This can help indicate a starting point for testing. If there is a related TCM loss of communication code, begin testing at the TCM. The same goes for ABS, BCM, and other modules with codes present alongside DTC U0073. Establish proper resistance at the Data Link Connector Determine the CANbus communication pins at the DLC with your vehicle wiring diagram. With your DVOM, probe the two pins while measuring resistance (ohms). Standard resistance for this test is approximately 60 ohms and it should hold steady. Monitor the resistance throughout your diagnosis for fluctuations, indicating when you've found the source of your communication problem. Wiggle Test CANbus Wires Begin your search for the source of your code by checking for breaks or loose connections that can cause high resistance, setting DTC U0073. If there was a specific module-related code along with U0073, begin at the module for that system and work your way back. Gently but firmly, wiggle the wires and connectors while monitoring the resistance on your DVOM. Resistance should hold steady if the circuit is good. If there are fluctuations in resistance, you've found an affected circuit. Locate the break in the wiring insulation. Perform a soldered repair and protect with weatherproof heat shrink. Clear the DTCs and retest. Check the Condition of Connectors Many times, water can penetrate into connectors and harnesses and form corrosion. The corrosion causes a poor connection and high resistance, either intermittent or constant, is experienced. Unplug connectors on the CANbus circuit and inspect for water or corrosion. Clean the connectors and apply dielectric grease to prevent recurrence. If the connector pins are damaged, splice in a new connector. Plug in all connectors firmly, ensuring the lock tabs are engaged. Check for Faulty Modules Should a module on the CANbus circuit experience an internal failure, DTC U0073 may set. If this is the case, your reference resistance will likely be high at the DLC. Unplug each module on the circuit, monitoring the resistance for changes. If the high resistance disappears when one module is unplugged, then reappears when reconnected, you've found your likely source. Check for bent pins, corrosion, or pushed-out connector pins. Repair as necessary. If the condition is still present, replace the module with a known good unit.
Codes Related to U0073
- U0100: Lost Communication With ECM/PCM
- U0101: Lost Communication With TCM
- U0102: Lost Communication With Transfer Case Control Module
- U0109: Lost Communication With Fuel Pump Control Module
- U0121: Lost Communication With ABS Control Module
- U0140: Lost Communication With Body Control Module (BCM)
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