U0402 on 2017-2018 Chrysler Pacifica: Implausible TCM Data Causes and Fixes

What's Unique About the 2017-2018 Chrysler PACIFICA

For the 2017-2018 Pacifica, this code is frequently linked to software issues that Chrysler has acknowledged in multiple Technical Service Bulletins (TSBs). Unlike many other vehicles where U0402 might immediately point to a bad part, on this platform, the first step is almost always to check for software updates. Furthermore, the Pacifica utilizes a dual-battery system (main and auxiliary) for its Engine Start-Stop (ESS) functionality. These control modules are highly sensitive to voltage, and a failing auxiliary battery is a known cause of various communication codes, including U0402. One TSB even instructs technicians to call a specific Chrysler engineer before attempting repairs on certain U0402 cases, highlighting that this can be a complex issue if not handled correctly.

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 gets stuck in one gear (limp mode).
• Erratic, harsh, or delayed shifting.
• Vehicle may stall or have trouble restarting.
• Transmission or stability control warning lights may illuminate.
• Message in EVIC: "Stop/Start Restart Required Fault Detected".
• Vehicle may not shift out of Park.

Most Likely Causes

1. Outdated Powertrain Control Module (PCM) Software 🔴 High Probability → Shop Engine Control Module (ECM) Chrysler has issued multiple TSBs (e.g., #18-001-19 REV B for 2018, #18-002-19 REV A for 2017) specifically to address this code with a software update. These bulletins explicitly list U0402-00 as a condition fixed by reprogramming the PCM.
   How to confirm: A Chrysler dealership or a qualified shop with a wiTECH scan tool must check the current software calibration ID against the latest available updates in the manufacturer's database.
   Typical fix: Reprogramming (flashing) the PCM with the latest software version. This is typically a 0.5-1.0 hour labor charge at a dealership.
   Est. part cost: $0
2. Low Battery Voltage or Failing Main/Auxiliary Battery 🟡 Medium Probability → Shop Vehicle Battery The Pacifica's Engine Start-Stop (ESS) system relies on both a main and an auxiliary battery. Control modules are highly sensitive to voltage, and a failure in either battery can cause widespread, seemingly unrelated electronic issues and communication codes. The TSBs for U0402 are often accompanied by battery state-of-charge codes (P00FD), indicating a direct link.
   How to confirm: Test both the main and auxiliary batteries and the charging system. A healthy system should have ~12.6V with the engine off and the alternator should produce 13.5-14.5V with the engine running. A weak auxiliary battery is a common culprit. 🎬 Watch: How to replace the auxiliary battery to fix Start/Stop faults.
   Typical fix: Charge or replace the weak battery (or both). In some cases, simply disconnecting the negative terminal for a few minutes can reset the modules and temporarily clear the fault.
   Est. part cost: $150-$500
3. Faulty Transmission Control Module (TCM) ⚪ Low Probability → Shop Transmission Assembly
   How to confirm: This is diagnosed by exclusion. If the software is up-to-date, both batteries are healthy, and wiring is intact, the TCM itself is the likely culprit. A technician may attempt to re-flash it first before recommending replacement.
   Typical fix: Replace the Transmission Control Module. The new module will require programming to the vehicle's VIN.
   Est. part cost: $400-$850
4. Wiring or Connector Issues ⚪ Low Probability Owners on other platforms have reported water intrusion into main harness connectors causing this code, suggesting a potential vulnerability in the wiring harness design.
   How to confirm: Visually inspect the wiring harness and connectors between the PCM and TCM for any signs of corrosion, damage, or loose pins. A multimeter can be used to check for continuity and proper voltage on the CAN bus wires.
   Typical fix: Repair the damaged section of the wiring harness or clean/replace the affected connectors. Applying dielectric grease can help prevent future corrosion.
   Est. part cost: $20-$100

Rare But Worth Checking

• Internal Transmission Failure: → Shop Transmission Assembly TSB #9003785 for the 2017 model suggests that a U0402 code can be related to a serious internal transmission concern, requiring specialized technician support before proceeding with repairs. This is a diagnosis of last resort after all other software and electrical causes have been ruled out.

Diagnosis Steps

1. Scan for all stored trouble codes in all modules. Pay close attention to any other communication (U-codes) or battery (P-codes) that are present.
2. Check for Technical Service Bulletins (TSBs). This is the most critical step. Provide your VIN to a dealer to check for applicable software updates like TSB #18-001-19 REV B or #18-002-19 REV A.
3. Thoroughly test the battery and charging system. This MUST include both the main and auxiliary batteries. A weak auxiliary battery is a known culprit for random electronic faults.
4. If a software update is available, have a dealer or qualified shop perform the update. This is the most common fix. According to forum users, this typically costs one hour of labor, around $100-$185.
5. If software is current and batteries are good, perform a thorough visual inspection of the wiring harness and connectors between the PCM and TCM. Look for any visible damage, corrosion, or loose connections.
6. As a temporary reset, you can try disconnecting the negative battery terminal for 10-15 minutes to reset all modules. This may clear the code temporarily and restore normal function, further pointing 🎬 Try this quick 3-minute TCM reset to improve harsh shifting. towards an electrical or software glitch rather than a hard mechanical failure.
7. If all the above steps do not resolve the issue, further diagnostics on the TCM itself are required, which may lead to its replacement.
8. As per TSB #9003785, if a transmission concern is present, consult a specialist as it may be an internal transmission fault.

Parts You'll Likely Need

• Powertrain Control Module (PCM) Software Update — This is the most common fix documented in Chrysler's own Technical Service Bulletins for the U0402 code on this vehicle.
  OEM price range: $100-$250
  Aftermarket price range: N/A
• Battery (Main or Auxiliary) — Low or unstable voltage from either the main or auxiliary battery is a common cause of communication faults between modules. The TSBs for U0402 also list battery state-of-charge codes.
  Trusted brands: Mopar, Interstate, Duralast
  OEM price range: $250-$400
  Aftermarket price range: $150-$250
• Transmission Control Module (TCM) (OEM #68315880AA, 68249614AA) — If software updates and battery checks do not resolve the issue, the TCM itself may have an internal fault.
  Trusted brands: Mopar
  OEM price range: $550-$850
  Aftermarket price range: $300-$500 (Refurbished)

Related Codes That Often Appear With This One

• P00FD — Battery -B- State Of Charge Performance, often seen in TSBs with U0402, suggesting low voltage from the main or auxiliary battery can be a root cause.
• U145D-00 — Implausible Data Received From TCM On D-PT, another TCM communication code listed in the same TSBs.
• U1465-00 — Implausible Driver Shift Request Signal Received, also listed in the same TSBs, pointing to a network communication problem related to the transmission.
• P0607-00 — ECU Internal Performance, listed in TSBs, indicating a potential module performance issue.
• P06E9 — Engine Starter Performance, another code addressed by the same PCM software update in TSB 18-002-19 REV A.

Technical Service Bulletins (TSBs) & Recalls

• 18-001-19 REV B: Flash: Powertrain Control Module (PCM) Updates, which includes a fix for U0402-00 for 2018 models.
• 18-002-19 REV A: Flash: Powertrain Control Module (PCM) Updates, which includes a fix for U0402-00 for 2017 models.
• 9003785: Advises technicians to call a specific expert for transmission concerns involving DTC U0402 on 2017 models.

Platform-Specific Known Issues

• TSB #18-001-19 REV B for the 2018 Pacifica lists U0402-00 as a code that can be resolved by a PCM software update. The update also addresses issues like ESS battery dry-out and engine stall during panic braking.
• TSB #18-002-19 REV A for the 2017 Pacifica also lists U0402-00 in a list of codes related to various module performance issues fixed by a PCM flash.
• TSB #9003785 for the 2017 Pacifica specifically warns technicians

Mechanic-Grade Diagnostic Values

• CAN Bus Network Resistance — expected: ~60 Ohms. Failure: A reading of ~120 Ohms indicates a missing terminating resistor or an open in the circuit. A reading of 0 Ohms indicates a short circuit.
• TCM Power Supply Voltage (Key On) — expected: 11.5V - 13.5V. Failure: Voltage below 11.5V can cause the module to reset or send incomplete data frames.
• Charging System Voltage (Engine Running) — expected: 13.5V - 14.5V. Failure: Voltage outside this range indicates a problem with the alternator or voltage regulator, which can cause module communication errors.

Hidden / Shadow Codes Worth Checking

• U0402-00: The '-00' is a symptom byte that often accompanies the main DTC on Chrysler vehicles. While not truly 'hidden', it can provide extra context for dealer technicians. In this case, it specifies 'Implausible Data Received From TCM' without further subtype information, as seen directly in the TSBs. (see via A professional scan tool like wiTECH will display the code with its symptom byte.)

Scan Tool Commands That Help

• wiTECH: TCM VIN Verify/Rewrite — This function is used after replacing the TCM to program the vehicle's VIN into the new module. A VIN mismatch will set a fault code and prevent proper operation.
• wiTECH: Valve Body Solenoid Learn — After a transmission or TCM replacement, this procedure is necessary to calibrate the new components and ensure smooth shifting.
• wiTECH: Clear All Adaptive Values — This resets the transmission's learned shift patterns. It can be useful after a repair to force the TCM to relearn, potentially improving shift quality.
• wiTECH: ECU Flash — This is the primary function used to load updated software onto the PCM or TCM as instructed by TSBs to resolve the U0402 code.

Real Owner Repair Stories

• pacificaforums.com user (2018 Chrysler Pacifica Touring L Plus) — Check engine light on, code U0402. Vehicle went into limp mode.
  ❌ Tried (didn't work) Initial diagnosis at an independent shop could not resolve the issue.
  ✅ What actually fixed it The user took the vehicle to a Chrysler dealer. The dealer performed a software update on the Powertrain Control Module (PCM) which resolved the code and the limp mode condition. The repair was covered under the 8-year/80,000-mile federal emissions warranty.

When the Usual Fixes Don't Work

• While software updates and battery issues are the most common causes, a non-scanner procedure to reset the TCM's adaptive memory exists. This involves a sequence of turning the ignition on (without starting the engine), pressing and holding the accelerator pedal for 10 seconds, turning the ignition off, and then waiting for two minutes before starting the car. Some owners attempt this to improve harsh shifting, and while it won't fix an underlying software bug that requires a reflash, it can sometimes clear temporary glitches in the adaptive learning tables.

OEM Part Supersession History

• 68294293AB → 68383660AE — Part was updated by the manufacturer. This specific part is a Transfer Case Control Module, not the TCM, but shows a typical supersession path for related electronics on similar platforms.

Model Year Variations Within This Range

• 2018: For the 2018 model year, Chrysler made the previously optional 7-inch Uconnect touchscreen standard, replacing the 5-inch unit. Both the 7-inch and optional 8.4-inch systems were updated to support Apple CarPlay and Android Auto. A new, lower-priced 'L' trim was introduced. While these are not direct causes for U0402, the updated hardware and software could have subtle differences in diagnostic paths compared to the 2017 model.
• 2017 vs 2018: The base engine, a 3.6L V6 with 287 horsepower, and the 9-speed automatic transmission remained the same for both model years. There were no major powertrain changes that would fundamentally alter the causes of code U0402 between these two years.