U0104 on 2025 Ram 1500: Lost Communication With Cruise Control Module Fixes

What's Unique About the 2025-2025 Ram 1500

For the 2025 Ram 1500, this code is exceptionally well-documented by the manufacturer as a software issue, not a hardware failure. Multiple Technical Service Bulletins (TSBs) were released for brand-new trucks, indicating a problem where the code would set and fail to clear on its own. The TSB snippets indicate the fault may be triggered during a cold start (engine coolant temperature below 122°F/50°C). Unlike on older vehicles where this code often points to wiring or module failure, on this specific truck, the very first diagnostic step should be checking if the software has been updated by a dealer.

Diagnostic Flowchart

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

Symptoms You May Notice

• Cruise control is inoperative or unavailable
• Check Engine Light (Malfunction Indicator Lamp, MIL) is illuminated
• A 'Service Adaptive Cruise Control' or similar warning message may appear on the dashboard
• Cruise control indicator on the instrument cluster may flash or stay illuminated.

Most Likely Causes

1. Powertrain Control Module (PCM) Software Needs Update 🔴 High Probability → Shop Engine Control Module (ECM) This specific issue is documented by Ram in Technical Service Bulletin #18-031-25 (Revisions A, B, and C) for the 2025 model year. The bulletin explicitly states a software update will allow this permanent fault code to clear naturally. The TSB mentions the fault can set on cold starts (coolant temp < 122°F).
   How to confirm: A Ram dealer or a qualified shop with access to OEM service information (like DealerCONNECT) can check the vehicle's software version against the latest version specified in the TSB using your VIN.
   Typical fix: Reprogramming the Powertrain Control Module (PCM) with the latest software version using the wiTECH scan tool. This must be done at a dealership or a properly equipped independent shop.
   Est. part cost: $0

Rare But Worth Checking

• Poor Power or Ground to Cruise Control Module: → Shop Cruise Control Module While software is the most likely culprit on this specific model, basic electrical issues are always a possibility. This includes a blown fuse (check fuse #82 in the under-hood panel), or a corroded/loose ground wire preventing the module from powering on.
• Damaged Wiring or Connectors: The CAN bus wiring harness that connects the modules can be damaged by chafing, corrosion, or impact. The Adaptive Cruise Control (ACC) module is located in the front bumper/grille area, making its wiring susceptible to front-end damage. A visual inspection of the harness is a valid diagnostic step if the software update does not resolve the issue.
• Faulty Cruise Control Module (CCM/ACC): → Shop Cruise Control Module It is possible for the module itself to fail, but this should be considered only after the software has been updated and all wiring/power has been checked and confirmed to be good. A replacement module will also require programming/calibration by the dealer.
• Faulty Brake Light Switch: A malfunctioning brake light switch can prevent the cruise control system from engaging, though it typically sets other codes. However, it's a known cause for inoperative cruise control on Ram trucks.

Diagnosis Steps

1. Contact a Ram dealership and provide your Vehicle Identification Number (VIN). Ask if Technical Service Bulletin #18-031-25 or any superseding software updates apply to your truck and if they have been performed.
2. If the update has not been performed, schedule an appointment to have the Powertrain Control Module (PCM) reprogrammed. This is the most likely fix.
3. If the software is already up-to-date or the flash does not fix the issue, proceed with traditional diagnostics.
4. Check the fuses related to the cruise control system in the under-hood fuse box (TIPM). Specifically, check fuse F82.
5. Inspect the wiring harness and connectors going to the Adaptive Cruise Control (ACC) module for any signs of damage, corrosion, or loose pins. The module is located in the lower front bumper area.
6. Using a multimeter, verify that the ACC module is receiving proper power (12V+) and has a solid ground connection. The module should not receive less than 10 volts.
7. Check the CAN bus termination resistance. With the battery disconnected, measure resistance between CAN-High (Pin 6) and CAN-Low (Pin 14) at the DLC; it should be approximately 60 ohms. A reading of 120 ohms suggests a problem with one of the two terminating resistors in the network.
8. If all wiring, power, and grounds are good, the Cruise Control Module itself may be faulty and require replacement and dealer programming.

Parts You'll Likely Need

• Powertrain Control Module Software Update — This is not a physical part, but a service. It is the most common and manufacturer-recommended fix for this code on a 2025 Ram 1500, as per TSB #18-031-25.
  Trusted brands: Mopar
  OEM price range: $150-$250
  Aftermarket price range: N/A
• Adaptive Cruise Control Module (OEM #68456215AE (supersedes 68456215AC, 68456215AD)) — This part, also called the radar sensor, should only be replaced if the software update and wiring checks do not solve the problem. It is a rare but possible point of failure.
  Trusted brands: Mopar
  OEM price range: $400-$600
  Aftermarket price range: $250-$450

Related Codes That Often Appear With This One

• U0405 — This code, 'Invalid Data Received From Cruise Control Module,' is often set alongside U0104. The official TSBs for the 2025 Ram 1500 list both codes as being resolved by the same software update.
• P1CEA-00 — Mentioned in TSB #18-031-25 as another code that may be present along with U0104 and is addressed by the software flash.
• P2AF6-00 — Also mentioned in TSB #18-031-25 as a related code resolved by the software update.

Technical Service Bulletins (TSBs) & Recalls

• 18-031-25 REV. C: Specifies that a software update will allow the permanent U0104-00 fault code to clear naturally. Notes condition may be set when coolant temp is less than 50°C (122°F).
• 18-031-25 REV. B: Notes that a software flash will address the U0104-00 code in Active or Stored status.
• 18-031-25 REV. A: Mentions that U0104-00 and U0405 may be set along with other codes and are addressed by a software flash.
• 18-031-25: The original bulletin linking U0104 and U0405 to a software flash fix.

Platform-Specific Known Issues

• A widely documented software issue on 2025 models causes U0104 and U0405 to set and become 'permanent,' meaning they cannot be cleared with a standard scan tool until a specific software update is performed by a dealer, as outlined in TSB #18-031-25.
• The TSBs indicate the fault may be triggered during cold engine starts, when coolant temperature is below 122°F (50°C).

Mechanic-Grade Diagnostic Values

• CAN C Bus Termination Resistance — expected: 53.5 to 67 Ohms. Failure: A reading near 120 Ohms indicates an open in the bus or a problem with one of the two terminating resistors. A reading near 0 Ohms indicates a short between the CAN High and Low wires.
• CAN C Bus Voltage (Key On, Engine Off) — expected: CAN High (Pin 6 at DLC): ~2.7V, CAN Low (Pin 14 at DLC): ~2.2V in the recessive state.. Failure: Voltages shorted to ground (0V), shorted to power (~5V or 12V), or stuck at a specific level indicate a bus fault.
🎬 Watch: Troubleshooting a Ram 1500 interior CAN bus fault
• ACC Module Power Supply Voltage — expected: 12V+ (Battery Voltage). Failure: Voltage dropping below 10.0 volts for more than 15 seconds can set a fault.
• ACC Module Ground Circuit Resistance — expected: Less than 5.0 Ohms. Failure: High resistance (greater than 5.0 Ohms) indicates a poor ground connection, which can cause the module to malfunction.

Hidden / Shadow Codes Worth Checking

• U0104-00: The '-00' suffix is a symptom byte indicating 'No Sub Type Information.' For this specific vehicle, the TSBs note that this code can become 'permanent' and will not clear with a standard scan tool until a specific PCM software update is performed. (see via A professional scan tool or the dealer's wiTECH tool will display the code with its symptom byte.)

Scan Tool Commands That Help

• wiTECH: Restore Vehicle Configuration — This function is critical after reprogramming or replacing a module (like the PCM, BCM, or ACC). It forces the module to adopt the master configuration file from the vehicle's gateway, resolving mismatches that can cause communication codes.
• wiTECH: Network View / ECU View — Used during initial diagnosis to see a topology map of all modules on the network. This quickly confirms if the ACC module is not communicating ('offline') versus communicating but setting a fault.
• wiTECH: Flash ECU — This is the primary repair procedure identified in TSB #18-031-25 to load the updated software into the PCM that corrects the U0104 permanent fault condition.

Wiring & Ground Locations

• CAN C Star Connectors (IP and Dash) — Chrysler/Ram vehicles use star connectors as junction points for the CAN bus. On 5th Gen Rams, there is typically one located behind the instrument panel (IP) on the driver's side and another behind the glove box area on the passenger side (Dash).. These connectors allow a technician to isolate different branches of the CAN bus. If a module or wire on one branch is causing a network-wide fault, unplugging that branch from the star connector will restore communication to the rest of the modules, pinpointing the location of the problem.
• ACC Module Ground Circuit (Z909) — This refers to the ground wire in the ACC module's harness connector. The physical ground point is on the chassis near the front of the vehicle, but the critical test is at the module's connector itself.. A high-resistance or open ground will prevent the ACC module from powering on and communicating, directly causing a U0104 code. Resistance should be checked from the ground pin at the connector to a clean point on the chassis.

Real Owner Repair Stories

• 5thGenRams Forum user 'jfcody3962' (2020 Ram 1500) — Auto high-beams not working, Aero Mode not working.
  ❌ Tried (didn't work) Dealer initially stated the truck was running the current software version and that there was 'nothing wrong' or 'no option to reconfigure'.
  ✅ What actually fixed it The owner showed the dealer a forum thread discussing the issue. The dealer then performed a 'Reconfigure the BCM' using the wiTECH tool, which resolved both the auto high-beam and the previously unnoticed inoperative Aero Mode issues. This highlights that a 'reconfiguration' can be necessary even when no 'update' is available.
• Ram Heavy Duty Forum user 'Harv91' (2019 Ram 2500) — Adaptive cruise and regular cruise not working, 'service required' message appears after the system cycles on/off five times at startup.
  ❌ Tried (didn't work) Cleaning the camera and radar sensor., Repairing loose pins in the module connector.
  ✅ What actually fixed it The user performed detailed diagnostics, confirming 12V power, good ground, and correct CAN bus voltages (2.7V/2.2V). Despite this, the module (DASM) would not appear on the scan tool. The final diagnosis from a dealer tech was a likely internal failure of the cruise control module itself. The thread did not have a final confirmation post-repair, but it serves as an excellent example of diagnosing beyond the software issue.

OEM Part Supersession History

• 68456215AC, 68456215AD → 68456215AE — Standard part revision and improvement by the manufacturer.
  Heads up: No incompatibility is noted. The latest part number (68456215AE) is the correct service replacement for the previous versions.

Model Year Variations Within This Range

• 2025: On 2025 Ram 1500 models equipped with the optional 'Hands-Free Driving Assist' system, there is no longer a 'regular' or 'standard' cruise control mode. The only available function is Adaptive Cruise Control (ACC). This is a change from previous models where holding the cruise control button could toggle between ACC and standard cruise.