U0402 on 2021 Chrysler 300: Implausible Data from TCM Causes and Fixes

What's Unique About the 2021-2021 Chrysler 300

The 2021 Chrysler 300 is built on the LX platform and uses a sophisticated, electronically controlled ZF-designed 8-speed automatic transmission (such as the 850RE or 8HP50). The integration between the transmission's controller (TCM) and the Powertrain Control Module (PCM) is critical and highly sensitive to software calibration. For this platform, communication errors like U0402 are frequently traced back to software anomalies. Chrysler released Technical Service Bulletin (TSB) 18-013-22 specifically to address a list of communication DTCs, including U0402, by reprogramming the PCM with updated software. This indicates it's a known issue that requires a specific software fix rather than immediate hardware replacement.

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 warning light is on
• Vehicle enters 'limp mode' (stuck in one gear)
• Erratic, harsh, or delayed shifting
• Delayed or no gear engagement from Park to Drive
• Traction control or stability control light may illuminate
• Loss of Anti-lock Brake System (ABS) and cruise control

Most Likely Causes

1. Outdated or Corrupt PCM/TCM Software 🔴 High Probability Modern vehicle electronics often have software bugs that are fixed with updates. TSB 18-013-22 directly addresses U0402 on 2021 models, recommending a PCM software flash to resolve a list of communication faults. This is the most common and manufacturer-acknowledged fix.
   How to confirm: A dealership or qualified shop with a wiTECH factory scan tool can check the current PCM software version against the latest available from Chrysler.
   Typical fix: Update the software for the Powertrain Control Module (PCM) using the wiTECH Diagnostic Application. The TSB specifies this action to correct the condition.
   Est. part cost: $0-$0
2. Low Battery Voltage or Charging System Fault 🟡 Medium Probability → Shop Vehicle Battery Control modules are extremely sensitive to voltage. A weak battery, failing alternator, or poor ground can cause communication glitches on the CAN bus. Chrysler TSBs for software flashing explicitly require connecting a battery charger to maintain stable voltage (between 13.2 and 13.5 volts) to prevent flash failure and data corruption.
   How to confirm: Test the battery and charging system. The battery should have approximately 12.6 volts with the engine off and 13.5-14.5 volts when running. Check for clean, tight terminals and solid ground connections.
   Typical fix: Charge or replace the battery. Repair the charging system (e.g., replace the alternator) or fix bad ground connections.
   Est. part cost: $150-$400
3. Failing Transmission Control Module (TCM) ⚪ Low Probability → Shop Transmission Assembly While less common than software issues, the TCM can fail internally, causing it to send corrupted data. This is a diagnosis of exclusion after software and electrical issues are ruled out. A user with a 2021 Chrysler 300 reported similar symptoms that were resolved by replacing a defective TCU (TCM).
   How to confirm: This is a process of elimination. If the PCM software is up-to-date per TSBs, the battery/charging system is good, and the wiring is intact, the TCM itself becomes the likely culprit.
   Typical fix: Replace the Transmission Control Module and program it to the vehicle. This must be done by a dealer or a specialized shop with programming capabilities.
   Est. part cost: $500-$1200
4. Wiring Harness or Connector Issue ⚪ Low Probability The CAN bus wiring harness between the PCM and TCM can become damaged from heat, vibration, or corrosion, disrupting communication. A forum user on a related platform noted that checking for bent pins or loose connectors at the TCM and transmission is a key diagnostic step.
   How to confirm: Visually inspect the wiring harness for chafing, melting, or corrosion. Check for continuity and resistance on the CAN bus wires with a multimeter. A healthy CAN bus should have a termination resistance of approximately 60 ohms.
   Typical fix: Repair the damaged section of the wiring harness or clean/replace the affected connectors. Apply dielectric grease to protect connectors.
   Est. part cost: $20-$200

Rare But Worth Checking

• Faulty Powertrain Control Module (PCM): → Shop Engine Control Module (ECM) While possible, the PCM is rarely the cause. The module receiving the bad data (PCM) is usually not the one generating it. However, an internal PCM failure could misinterpret good data.
• Faulty Sensors Feeding the TCM: A failing sensor (e.g., transmission speed sensor) could provide the TCM with illogical data, which the TCM then broadcasts over the network, triggering the U0402 in the PCM. This would likely be accompanied by other sensor-specific DTCs.

Diagnosis Steps

1. Scan for all diagnostic trouble codes from all modules to get a full picture of network health. Note any codes listed in TSB 18-013-22.
2. Check the battery and charging system. Ensure voltage is stable and within the 13.5-14.5V range when the engine is running. A battery load test is recommended.
3. Check for Technical Service Bulletins (TSBs). Specifically, reference TSB 18-013-22 for 2021 Chrysler 300 models.
4. Using a wiTECH scan tool, verify the PCM has the latest software. If not, perform the software update as described in the TSB. Ensure a stable power supply (battery charger) is used during the flash.
5. Visually inspect the wiring harness and connectors between the TCM and PCM. Look for damage, corrosion, or loose pins. Pay attention to grounds.
6. With the ignition off, measure the resistance of the CAN bus at the OBD-II port. It should be approximately 60 ohms, indicating good termination resistors.
7. If all previous steps fail, the Transmission Control Module (TCM) is likely faulty and requires replacement and programming.

Parts You'll Likely Need

• Transmission Control Module (TCM) (OEM #68347573AA (Note: This is for a related application and may not be exact for a 2021 300. VIN confirmation is required)) — If software updates and wiring/power checks don't solve the problem, the module itself is the most likely point of failure.
  Trusted brands: Mopar
  OEM price range: $800-$1200
  Aftermarket price range: $500-$900

Related Codes That Often Appear With This One

• U0101 — 'Lost Communication With TCM'. This code is listed alongside U0402 in TSB 18-013-22, indicating a pattern of communication faults that can be resolved with a PCM flash.
• U0403 — 'Implausible Data Received From T-Case'. Also listed in TSB 18-013-22, suggesting a systemic software issue affecting multiple modules.
• U0140 — 'Lost Communication With Body Control Module'. Another code mentioned in TSB 18-013-22, reinforcing that the root cause is often a central communication software problem in the PCM.

Technical Service Bulletins (TSBs) & Recalls

• TSB 18-013-22 (January 20, 2022): Titled 'Flash: Powertrain Control Module (PCM) Updates', this TSB applies to 2021 Chrysler 300s with the 3.6L engine. It directly lists U0402 - 'Implausible Data Received From TCM' as a code that can be resolved by flashing the PCM with new software.

Platform-Specific Known Issues

• NHTSA Technical Service Bulletin 18-013-22 is the primary document for this issue on 2021 models. It lists U0402 as part of a large group of communication DTCs that can be fixed by reprogramming the PCM. Symptoms can include MIL illumination, loss of shifting, or fixed third gear operation.

Mechanic-Grade Diagnostic Values

• CAN C Bus Voltage (Idle) — expected: ~2.5 V on both CAN-H and CAN-L lines at the DLC.. Failure: Significant deviation from 2.5V, or one line being stuck high or low, indicates a short or open.
• CAN Bus Termination Resistance — expected: ~60 Ω between Pin 6 (CAN-H) and Pin 14 (CAN-L) at the DLC with the battery disconnected.. Failure: A reading of ~120 Ω indicates one of the two terminating resistors is offline. A reading near 0 Ω indicates a short between the two lines.
• TCM Power Supply Voltage (Key On) — expected: 11.5 V - 13.5 V at the TCM power input pin.. Failure: Voltage below 11.5V can cause module instability and communication errors.

Hidden / Shadow Codes Worth Checking

• Environmental Data / Event Data: Chrysler vehicles store a snapshot of vehicle operating conditions at the time a DTC is set. This data, viewable on a wiTECH scan tool, can include vehicle speed, engine RPM, and transmission temperature, which helps in duplicating the fault. (see via This data is accessible within the specific DTC details on a wiTECH or equivalent advanced scan tool.)

Scan Tool Commands That Help

• wiTECH: Quick Learn — This procedure is required after replacing the TCM, valve body, or the entire transmission, or after clearing adaptation memory cells. It allows the TCM to relearn clutch fill times and adaptive values to ensure proper shift quality.
• wiTECH: PROXI Configuration Alignment — This function is mandatory after replacing the TCM. It updates the vehicle's configuration file (stored in the BCM) to recognize the new module, ensuring all other modules on the network can communicate with it correctly.
• wiTECH: VIN Verification — After flashing a TCM with new software, this routine must be performed to ensure the module is correctly programmed to the vehicle's Vehicle Identification Number.

Wiring & Ground Locations

• G901a — Located in the left front of the engine compartment.. This is a primary ground point for the Transmission Control Module on the LX platform. A loose or corroded connection at G901a can cause intermittent power loss or electrical noise, leading to data corruption and codes like U0402.
• TCM Main Connector — On the 8-speed transmission, the main round connector is on the passenger side of the transmission case. Access often requires lowering the transmission crossmember.. This is the single point of connection for all power, ground, and communication lines to the TCM. It's susceptible to heat and vibration, and a poor connection here will directly cause communication faults.
• Front Power Distribution Center Fuses — Under the hood, on the passenger side.. Fuse F29 (15A) and Fuse F37 are commonly associated with power supply to the TCM and shifter assembly. A loss of power from these fuses will cause a U0101 (Lost Communication) and can also lead to U0402.
• Rear Power Distribution Center Fuse — In the trunk, near the battery.. Fuse F26 in the trunk fuse box can also be part of the TCM power circuit. Verifying this fuse is crucial before diagnosing deeper wiring issues.

Real Owner Repair Stories

• YouTube - 'No Crank No Start! U0101 FIX!' (2012 Chrysler 300 AWD 3.6L (LX Platform, similar wiring to 2021)) — No crank, no start, and a U0101 'Lost Communication with TCM' code.
  ❌ Tried (didn't work) Checking fuses, which were all good., Checking for power at the fuse box, which was present.
  ✅ What actually fixed it The wire providing power from the front fuse box (Fuse 29) to the TCM connector had an internal break. Power was present at the fuse but not at the TCM connector (pin 13). The fix was to run a new wire from the fuse panel to the TCM harness near the transmission connector, bypassing the break in the factory harness.

OEM Part Supersession History

• 68293698AA, 68259190AB, 5150913AC → 68347574AA — Part has been updated multiple times for reliability and software compatibility.
  Heads up: This part number is for the 5-speed transmission but illustrates the frequent supersession of Chrysler TCMs. Using an older, non-superseded part number can re-introduce known software or hardware flaws. Always verify the latest part number with a dealer using the vehicle's VIN.