U0002 on 2013 Ram 2500: Causes and Fixes for CAN C Bus Off Performance

What's Unique About the 2013-2013 Ram 2500

For this specific model year, Ram issued multiple Technical Service Bulletins (TSBs) acknowledging that code U0002, along with others like U0100, could be triggered due to software anomalies. These bulletins provide an updated software calibration for the control modules to prevent the Malfunction Indicator Lamp (MIL) from illuminating when no actual hardware defect is present. This makes checking for a software update a crucial first step, potentially saving significant time and money on unnecessary hardware diagnostics. The issue was prevalent enough that Ram revised the TSBs multiple times to expand the list of affected DTCs and refine the software fix.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Generation note: While the software-related cause is most prominent for the 2013-2014 model years, the underlying potential for wiring and module failures causing a U0002 code exists across the 4th Generation of Ram HD trucks (2010-2018) and other Chrysler/Dodge/Ram vehicles sharing the same CAN architecture.

Symptoms You May Notice

• Multiple warning lights on the dashboard (Check Engine, ABS, Traction Control, Airbag)
• Engine may stall or not start
• Erratic or no response from the instrument cluster gauges
• Transmission may not shift correctly or may enter limp mode
• Loss of communication with various control modules when using a scan tool
• Message in the EVIC (Electronic Vehicle Information Center) like "Service Electronic Braking System".
• Radio or Uconnect screen may reboot, freeze, or go blank.
• Loss of power steering assist
• Wipers may turn on by themselves.

Most Likely Causes

1. Software Anomaly in Control Module 🔴 High Probability Manufacturer TSBs #18-091-16, #18-057-15 REV A, and #18-030-14 REV. B were specifically released to address this code being set without a true hardware fault. TSB 18-091-16 explicitly states the update is to "Prevent or reduce MIL illumination when no defect is present for... U0002 - CAN C Bus Off performance - Bus Off."
   How to confirm: Contact a Ram dealership with your vehicle's VIN to determine if any of these TSBs are open and applicable. The dealer's wiTECH scan tool can verify the current software calibration and perform the update.
   Typical fix: Update (reflash) the software in the Powertrain Control Module (PCM) to the latest version. This procedure must be done by a dealer or a qualified shop with the correct tools.
   Est. part cost: $0
2. Wiring Harness Short or Open 🟡 Medium Probability Wiring harnesses can rub against chassis or engine components, leading to chafing and short circuits. A common area for rodent damage is in the passenger footwell. Connectors, especially the main connector on the ABS module behind the front driver's side wheel well, are prone to corrosion.
   How to confirm: Perform a thorough visual inspection of the CAN C bus wiring, paying close attention to the harness near the ABS module and where it passes through the firewall. With the battery disconnected, use a multimeter to check for approximately 60 ohms of resistance between Pin 6 (CAN C+) and Pin 14 (CAN C-) at the OBD-II port. 🎬 Watch: How to test CAN bus resistance with a multimeter A reading of 120 ohms suggests an open circuit or bad terminating resistor, while near 0 ohms indicates a direct short.
   Typical fix: Repair the damaged section of the wiring harness or clean/reseat the affected connector. In cases of rodent damage, multiple wires may need to be spliced.
   Est. part cost: $5-$50
3. Faulty ABS Control Module 🟡 Medium Probability The ABS module is a frequent point of failure on these trucks and is a primary node on the CAN C bus. An internal failure in the ABS module can corrupt the entire network, causing a U0002 code along with ABS and traction control warnings. Forum users report repeated issues with replacement ABS modules as well.
   How to confirm: This is often a process of elimination. If software is updated and wiring is confirmed good, disconnect the main electrical connector from the ABS module. If the other modules on the network begin communicating again and the bus resistance returns to a normal value (typically 120 ohms with one terminating module disconnected), the ABS module is the likely culprit.
   Typical fix: Replace the failed ABS module. The replacement module will require programming/calibration by a dealer or a specialized shop to function correctly with the vehicle. OEM part numbers include 68143491AA and 68204539AC (superseded by 68204539AJ). 🎬 Watch this helpful overview of the ABS module repair process
   Est. part cost: $300-$600

Rare But Worth Checking

• Faulty Star Connector (CAN Bus Hub): The star connectors act as hubs for the CAN bus wiring. On these trucks, CAN C and IHS hubs are located under the dash near the steering column. While rare, corrosion or a poor connection within these hubs can disrupt the network. Diagnosis involves checking for continuity through the hub.
• Aftermarket Electronics: Improperly installed aftermarket devices like remote starters, alarms, or even plug-in devices like power steps connected to the OBD-II port can interfere with or short out the CAN bus network, causing communication errors. One owner on a forum fixed their issue by reseating the OBD-II connector for their AMP power steps.
• Faulty Radio/Uconnect Module: The radio is an active module on the CAN bus. A failing Uconnect head unit can broadcast corrupt data, bringing down the network. Symptoms often include the radio freezing or rebooting on its own. If disconnecting the radio module restores network stability, it is the source of the fault.
🎬 See a real-world diagnosis of Ram CAN bus communication issues

Diagnosis Steps

1. Check for TSBs: Contact a Ram dealer with your VIN to see if TSBs #18-091-16, #18-057-15 REV A, or #18-030-14 REV. B apply. If so, have the recommended PCM software update performed first. This is the most common fix.
2. Check Battery and Grounds: Ensure the battery is fully charged (above 12.4V) and the alternator is functioning correctly (13.5-14.5 volts when running). Low voltage can cause unpredictable module behavior. Verify that all main ground connections to the chassis and engine are clean and tight.
3. Visual Inspection: Thoroughly inspect all visible wiring harnesses. Pay special attention to the harness leading to the ABS module (located in the driver's side front wheel well) for chafing or corrosion. Also check harnesses in the passenger footwell for potential rodent damage.
4. Measure Bus Resistance: Disconnect the battery. Use a quality multimeter to measure the resistance between Pin 6 (CAN C High) and Pin 14 (CAN C Low) at the OBD-II port. A healthy bus will read approximately 60 Ohms. A reading of 120 Ohms indicates an open in the circuit or a disconnected terminating module. A reading near 0 Ohms indicates the CAN High and Low wires are shorted together.
5. Isolate the Faulty Module/Branch: If the resistance reading is incorrect, begin disconnecting modules from the CAN C network one by one. Start with the most likely culprits: the ABS module and the Radio. After unplugging each module, re-measure the resistance at the OBD-II port. The fault lies with the module or wiring branch that, when disconnected, causes the resistance to return to a normal value (e.g., from 0 Ohms to 60 Ohms, or from 120 Ohms to 60 Ohms).
6. Check for Shorts to Power/Ground: With the battery disconnected, check for continuity between CAN C High (Pin 6) and ground, and CAN C Low (Pin 14) and ground. There should be no continuity. Then, with the battery reconnected and key on, carefully check for voltage on CAN C High and Low. Normal readings are around 2.5V; any reading near battery or ground voltage indicates a short.
7. Advanced Diagnostics: If the problem is intermittent, an oscilloscope is the bes

Parts You'll Likely Need

• No Specific Part - Diagnosis is Key — U0002 is a network fault, not a component failure code. The 'fix' is often a software update or a wiring repair. If a part is needed, it will be the specific module (e.g., ABS module, PCM, TCM) that is identified as faulty during diagnosis, and the part number will vary.
• ABS Control Module (OEM #68204539AC, 68204539AJ, 68143491AA) — The ABS module is a common failure point on this platform that can cause a U0002 code. If diagnosis points to the module, it must be replaced.
  Trusted brands: Mopar
  OEM price range: $300-$500
  Aftermarket price range: $200-$400 (Remanufactured)

Related Codes That Often Appear With This One

• U0100 — Lost Communication With ECM/PCM. This code is frequently logged with U0002 because if the CAN bus is down ('Bus Off'), no modules can communicate with the ECM/PCM. It is specifically mentioned in the same TSBs as U0002.
• U0126 — Lost Communication With Steering Angle Sensor Module. The steering angle sensor is another module on the CAN bus, and its communication will be lost if the bus is down.
• U0415 — Invalid Data Received From Anti-Lock Brake System Control Module. This indicates the data from the ABS module is corrupt or missing, which is a direct symptom of a CAN bus failure and often points towards the ABS module itself being the source of the problem.
• U0101 — Lost Communication with TCM. Similar to U0100, if the CAN bus fails, the Transmission Control Module cannot communicate with other modules.

Technical Service Bulletins (TSBs) & Recalls

• 18-091-16: Addresses MIL illumination for U0002 when no defect is present.
• 18-057-15 REV A: Also mentions improvements to prevent false MIL illumination for U0002.
• 18-030-14 REV. B: Cites U0002 in a list of codes affected by a software update that changes diagnostic fault trip logic.

Platform-Specific Known Issues

• Mandatory Software Update Check: A series of TSBs were issued for the 2013 Ram 2500 to correct software logic that could falsely trigger U0002. Bulletin #18-091-16 notes, "Improvements to prevent or reduce MIL illumination when no defect is present for: U0002 - CAN C Bus Off performance - Bus Off." This should always be the first step in diagnosis.
• ABS Module Connector Corrosion: Owners on forums like RamForum.com frequently report that the main electrical connector on the ABS module, located in the driver's side wheel well, is susceptible to water intrusion and corrosion, leading to intermittent CAN bus faults. Applying dielectric grease after cleaning is a recommended preventative measure.
• Rodent Damage in Passenger Footwell: A user on RamForum.com shared a detailed story of their truck failing to start and throwing multiple communication codes. The cause was found to be rodent damage to a CAN bus connector located in the passenger footwell. After repairing the chewed wires, the truck started, though some HVAC issues remained until codes could be properly cleared.

Mechanic-Grade Diagnostic Values

• CAN C Bus Resistance (at OBD-II Port) — expected: 53.5 to 67 Ohms. Failure: Near 0 Ohms = Short between CAN +/- wires. ~120 Ohms = Open circuit or one terminating resistor offline. Above 67 Ohms = High resistance in wiring.
• CAN C Bus (+) Voltage to Ground (Key On) — expected: ~2.5 Volts. Failure: 0 Volts may indicate a short to ground. Above 2.7V or near battery voltage indicates a short to power.
• CAN C Bus (-) Voltage to Ground (Key On) — expected: ~2.5 Volts. Failure: Above 10.0 Volts indicates a short to voltage. Near 0V can indicate a short to ground.
• Resistance of CAN C wiring from Star Connector to a module connector — expected: Below 5.0 Ohms. Failure: Resistance above 5.0 Ohms indicates an open or high resistance in that wiring branch.

Scan Tool Commands That Help

• wiTECH 2.0: Loss of Comm Test — This function continuously 'pings' all expected modules on the network every 100 milliseconds. It is used to identify an intermittent module that is dropping off the network, which may not be caught with a standard DTC scan. The tool will highlight any module that fails to respond, helping to pinpoint the source of a Bus Off event.

Wiring & Ground Locations

• CAN C Star Connector — On 2013+ models, the primary CAN C hub (Star Connector, also called a 'diagnostic can-c connector') is often located under the instrument panel, sometimes accessible by removing the panel around the headlight switch or in the passenger footwell area. It serves as a central junction point for the bus.. This is the central point for network diagnostics. A technician can disconnect individual branches of the CAN bus here to isolate a faulty module or wiring short that is bringing the entire network down.
• G300 / G301 — There are major ground points located on the driver's side inner fender, below or near the battery. These are critical chassis grounds for multiple systems.. A corroded or loose main ground connection at this point can cause floating voltages and communication errors across multiple modules, leading to a U0002 code. The connection can look visually okay but be corroded internally.
• ABS Module Connector — Located in the driver's side front wheel well, behind the fender liner.. This connector is exposed to the elements and is a common point for corrosion and water intrusion, which can short the CAN C pins (Pins 25 & 26 on some diagrams) and cause a bus failure.
• Instrument Cluster (CCN) — In the dashboard, behind the steering wheel.. The Instrument Cluster (Cab Compartment Node or CCN) can act as a gateway between different bus systems. A failure within the cluster can disrupt communication, and in some cases, it contains a terminating resistor for the bus.

Real Owner Repair Stories

• cumminsforum.com user (2013 Ram 2500) — Truck would not start, multiple warning lights, gauges not working, "no bus" message. Codes U0002 and U0100 present.
  ❌ Tried (didn't work) Checking all fuses., Checking wiring harness for visible damage., Replacing the ABS module., Replacing the PCM.
  ✅ What actually fixed it The Totally Integrated Power Module (TIPM), which acts as the central gateway, was faulty. Replacing the TIPM and having it programmed to the vehicle resolved all communication issues and codes.

OEM Part Supersession History

• 68204539AC → 68204539AJ — Revision and update by manufacturer. The supersession list includes multiple previous part numbers (AA, AB, AC, AD, AE, AG, AH).
  Heads up: While multiple part numbers have been used, the latest version 'AJ' replaces all prior versions for the 2013 model year. Note that some vendors list this part as discontinued, which may affect availability.