U0402 on 2015-2017 Ram Promaster City: Causes and Fixes for Implausible TCM Data

What's Unique About the 2015-2017 Ram PROMASTER CITY

The 2015-2017 Ram Promaster City is particularly known for this issue, as evidenced by multiple Technical Service Bulletins (TSBs) issued by Ram. These bulletins directly address U0402 and other related communication codes, with the prescribed fix being a software update for the Powertrain Control Module (PCM). One TSB for the 2017 model is highly unusual, instructing technicians to call a specific engineer at the manufacturer before attempting a repair, which highlights how specific and known this software-related issue is to Ram. A recall was also issued for 2015-2016 models for a corroded CAN-C connector near the driver's seat that could cause loss of communication with the TCM.

Diagnostic Flowchart

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

Symptoms You May Notice

• Check Engine Light is on
• Transmission may enter 'limp mode,' often locking into a single gear
• Harsh, erratic, or delayed shifting
• Inability to select gears
• Flashing transmission or traction control warning light on the dashboard.

Most Likely Causes

1. Outdated Powertrain Control Module (PCM) or Transmission Control Module (TCM) Software 🔴 High Probability → Shop Engine Control Module (ECM) Multiple manufacturer TSBs (#18-063-17, #1806417, #18-008-16 REV. B, 21-018-17) confirm that software glitches are a primary cause for this code on this specific vehicle.
   How to confirm: A technician at a Ram dealership can check for applicable TSBs and determine if the vehicle's modules have the latest software version using a wiTECH scan tool.
   Typical fix: Reprogramming the PCM and/or TCM with the latest manufacturer software.
   Est. part cost: $0
2. Failing Transmission Control Module (TCM) 🟡 Medium Probability → Shop Transmission Assembly If software updates do not resolve the issue, the module itself can fail internally, sending out corrupt data.
   How to confirm: After a software update fails to fix the code, a technician will test the TCM's power, ground, and communication circuits. If circuits are good, the module is condemned.
   Typical fix: Replace the Transmission Control Module and program it to the vehicle.
   Est. part cost: $200-$500
3. Wiring Harness or Connector Issue ⚪ Low Probability A recall for 2015-2016 models was issued for a low-voltage electrical harness connector (CAN-C 'Star' connector) near the driver's seat that is susceptible to water intrusion and corrosion, causing loss of communication to the TCM.
   How to confirm: Visually inspect the wiring harness between the PCM and TCM for any signs of chafing, breaks, or corrosion at the connectors. A multimeter is used to check for continuity and shorts in the CAN bus wires.
   Typical fix: Repair the damaged section of the wiring harness or clean/replace the affected connectors. The recall involves relocating the CAN-C connector to under the instrument panel.
   Est. part cost: $10-$100

Rare But Worth Checking

• Low Battery Voltage or Poor Grounds: → Shop Vehicle Battery A weak battery or faulty charging system can cause unpredictable communication errors across many modules. Always check battery health (should be above 11.5V under load) and ground connections before replacing expensive components.
• Faulty Powertrain Control Module (PCM): → Shop Engine Control Module (ECM) While possible, the PCM is less likely to fail than the TCM for this specific code. This should only be considered after all other possibilities, including software and the TCM, have been ruled out.

Diagnosis Steps

1. Connect a professional scan tool capable of reading manufacturer-specific codes and check all modules for DTCs.
2. Check for any open Technical Service Bulletins (TSBs) related to U0402 for your vehicle's VIN. This is the most critical step.
3. If a software update TSB is found, have a dealership or qualified shop with a wiTECH tool reprogram the PCM/TCM to the latest version.
4. Clear all codes and perform a road test to see if U0402 returns. If it does not, the repair is complete.
5. If the code returns, inspect the battery, charging system, and all main power/ground connections for the PCM and TCM.
6. Visually inspect the wiring harness and connectors between the PCM and TCM for any signs of damage, corrosion, or loose pins. Pay special attention to the CAN-C 'Star' connector near the driver's seat on 2015-2016 models, which was subject to a recall for corrosion.
7. Perform a CAN bus resistance check. With the battery disconnected, measure resistance between Pin 6 (CAN-H) and Pin 14 (CAN-L) at the OBD-II port. A healthy network should read approximately 60 ohms. A reading of 120 ohms indicates an open circuit or a problem with one of the two terminating resistors.
8. If wiring is intact, the TCM is the next most likely suspect. Test its circuits and if they are good, the TCM likely needs replacement.
9. If a new TCM is installed, a 'Proxy Alignment' procedure must be performed with a dealer-level scan tool (wiTECH) to configure the new module to the vehicle network.
10. As a final step, if a new TCM does not solve the issue, the PCM may be at fault.
🎬 Watch: A walkthrough of a 2017 ProMaster City transmission replacement.

Parts You'll Likely Need

• Transmission Control Module (TCM) (OEM #68467810AA) — This part is the second most likely cause if a software update does not fix the problem. It is the source of the 'implausible data'.
  Trusted brands: Mopar
  OEM price range: $400-$700
  Aftermarket price range: $200-$500

Related Codes That Often Appear With This One

• U1424 — Often appears with U0402 in TSBs, indicating 'Implausible Engine Torque Signal Received,' which is another symptom of the communication breakdown between the TCM and PCM.
• P1DD2 — Listed alongside U0402 in TSB #18-063-17 REV. A, this code for 'Torque Request Signal From TCM Denied' shows the PCM is actively rejecting the TCM's commands due to the implausible data.
• P0128 — This 'Thermostat Rationality' code is mentioned in the same TSBs, suggesting the software update addresses multiple unrelated logic faults at once.
• ECU Configuration Mismatch — This code often appears when a module has been replaced and not correctly configured to the vehicle's network, requiring a 'Proxy Alignment' procedure.

Technical Service Bulletins (TSBs) & Recalls

• 9003785: Instructs technicians to call a specific contact for transmission concerns with DTC U0402 on 2017 models.
• 18-063-17 REV. A: Involves a software update to fix U0402 along with other codes like U1424 and P1DD2-00.
• 18-063-17: Mentions U0402 as a code fixed by software enhancements.
• 1806417: Lists U0402 as a code that may be set and is addressed by a software enhancement.
• 18-008-16 REV. B: Groups U0402 with a long list of other DTCs that are resolved with a PCM software update.
• 21-018-17 REV. C: Supersedes previous bulletins and involves reprogramming the TCM with the latest software to address multiple DTCs 🎬 See a demonstration of the transmission shift alignment process. and improve shift quality.

Platform-Specific Known Issues

• A pattern of software-related faults causing this code is well-documented in Ram TSBs #9003785, #18-063-17 REV. A, #18-063-17, #1806417, and #18-008-16 REV. B.
• TSB #9003785 specifically instructs technicians working on a 2017 model with a transmission concern and code U0402 to contact a specific Chrysler engineer before proceeding with repairs, indicating a known, complex issue.
• The fix often involves a PCM software flash that corrects a bundle of unrelated trouble codes simultaneously, not just U0402.
• A recall was issued for 2015-2016 models due to potential corrosion in the CAN-C 'Star' connector located by the driver's seat, which can cause a loss of communication with the TCM and lead to the transmission shifting to neutral unexpectedly.

Mechanic-Grade Diagnostic Values

• CAN Bus Network Resistance — expected: Approximately 60 Ohms. Failure: A reading of 120 Ohms indicates an open in the circuit or a fault with one of the two terminating resistors. A reading near 0 Ohms indicates a short between the CAN High and CAN Low wires.
• CAN High Voltage (Key On) — expected: Average of ~2.6 Volts (fluctuates between 2.5V and 3.5V). Failure: No voltage or voltage outside the expected fluctuating range.
• CAN Low Voltage (Key On) — expected: Average of ~2.4 Volts (fluctuates between 1.5V and 2.5V). Failure: No voltage or voltage outside the expected fluctuating range.
• TCM Supply Voltage (Key On) — expected: 11.5V - 13.5V. Failure: Voltage drops or readings outside this range indicate a power supply or ground issue to the module.

Scan Tool Commands That Help

• wiTECH or equivalent dealer/J2534 tool: Proxy Configuration Alignment (Proxy Alignment) — This procedure is required after replacing a network module like the TCM. It synchronizes the new module with the vehicle's central configuration stored in the Body Control Module (BCM). Failure to perform this will cause the odometer to flash and can set 'ECU Configuration Mismatch' or communication codes.
• wiTECH: Reprogram TCM/PCM — This is the primary fix for U0402 when a relevant TSB exists. It updates the module's operating software to correct logic errors that cause the implausible data.

Wiring & Ground Locations

• CAN-C 'Star' Connector — Originally located by the front driver's seat in 2015-2016 models. A recall involved relocating it to under the instrument panel.. This connector is a junction point for the CAN-C communication network. It was found to be susceptible to water intrusion and corrosion, which directly interrupts communication between the TCM and other modules, causing U0402 and potentially causing the transmission to shift to neutral.
• Interior Fuse Panel — Located on the driver's side, under the instrument panel.. This panel contains fuses for various control modules, including potentially the TCM or related systems. A blown fuse here can cause a loss of power to a module, leading to communication codes.
• Underhood Fuse Box (Front Distribution Unit) — Located on the right side of the engine compartment, next to the battery.. Contains main fuses and relays for the powertrain, including the ECM and TCM power loads (Fuses F18, F19, F20). A fault here can cut power to the control modules.
• Chassis Ground — Multiple points on the vehicle's frame and body. A common practice is to find a bare metal spot on the chassis/frame to attach ground wires.. Poor ground connections for the TCM or PCM can introduce electrical noise or voltage drops, corrupting data signals on the CAN bus and triggering communication codes like U0402.

Real Owner Repair Stories

• Best Car Fixes (YouTube Channel) (2015-2016 Ram Promaster City 2.4L I4) — Hard shifting, transmission problems, multiple communication codes including 'ECU configuration mismatch'.
  ❌ Tried (didn't work) Clearing codes without addressing the configuration mismatch.
  ✅ What actually fixed it A 'Proxy Alignment' procedure was performed using a dealer-level tool (wiTECH). The scan tool showed the TCM was 'not configured or mismatched'. Running the alignment function successfully configured the module to the vehicle network, resolving the communication faults.

Model Year Variations Within This Range

• 2015-2016: These model years were subject to a specific recall (Chrysler S21) for a corroded CAN-C bus connector near the driver's seat that could cause loss of communication with the TCM. The fix involved inspecting, replacing if corroded, and relocating the connector.
• 2017: TSB #9003785 is highly specific to 2017 models, instructing technicians to call a named engineer at the manufacturer before attempting repairs for U0402, suggesting a unique or complex issue known for this year that differs from the earlier software and recall-related problems.