U0418 on 2021 Chrysler 300: Implausible Brake Module Data Explained

What's Unique About the 2021-2021 Chrysler 300

On modern Chrysler platforms like the 300 (LX platform), numerous control modules are deeply interconnected. A fault in one area can create a cascade of communication codes. As seen in TSB #18-013-22, U0418 often appears with a host of other 'U-codes', pointing towards a systemic issue like low voltage or a software bug rather than a single failed part. These vehicles are particularly sensitive to battery voltage, and a weak battery is a very common trigger for this specific code. TSBs for related platforms explicitly state that voltage dropping below 10 volts can erroneously set code U0418.

Diagnostic Flowchart

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

Symptoms You May Notice

• ABS warning light illuminated
• Traction Control or Electronic Stability Control (ESC) light illuminated
• Brake-related warnings on the instrument cluster
🎬 Watch: Common reasons why your Chrysler 300 ABS light is on
• Cruise control may be disabled
• In some cases, the vehicle may enter a reduced power 'limp mode'
• Brake pedal may feel soft or have a delayed response

Most Likely Causes

1. Low Battery Voltage or Weak Battery 🔴 High Probability Multiple Chrysler TSBs explicitly state that low battery voltage (below 10-12 volts) can erroneously set code U0418. Modern vehicles have a high electrical demand, and a weak battery can cause data corruption between modules during startup. Forum users across Chrysler platforms frequently report that replacing an aging battery resolves a host of electronic issues, including U0418.
   How to confirm: Perform a load test on the battery. A simple voltage check showing over 12V is not sufficient, as the voltage can drop under load. Many auto parts stores will do this for free. Also, check for loose or corroded battery terminals.
   Typical fix: Replace the vehicle's 12V battery and ensure terminals are clean and tight. In some cases, a full reset may require disconnecting the battery for 20-30 minutes. After a deep discharge event, an 'ABS Module Reset' with a dealer-level scan tool may be required to clear the code.
   Est. part cost: $150-$350
2. Control Module Software Glitch 🟡 Medium Probability Chrysler has issued multiple Technical Service Bulletins (TSBs) for various models where the fix for U0418 is to reprogram the Powertrain Control Module (PCM) with updated software. TSB #18-013-22 specifically applies to the 2021 Chrysler 300 for this issue.
   How to confirm: A dealer or a properly equipped independent shop can use a wiTECH scan tool to check the current software calibration ID of the PCM against the latest version available from Chrysler.
   Typical fix: Reprogram the PCM with the latest available software using a tool like wiTECH. This is typically a dealer-only service. The process requires a stable power supply to the vehicle to prevent interruption.
   Est. part cost: $0-$250
3. Wiring or Connector Issue ⚪ Low Probability Wiring harnesses can be subject to chafing, corrosion, or damage from road debris or improper repairs, leading to intermittent communication on the CAN bus. On related platforms, damaged wiring to a wheel speed sensor has been found to be the root cause.
   How to confirm: Visually inspect the wiring harness and connectors going to the ABS module for any signs of damage, corrosion, or loose pins. A professional can check for continuity and resistance on the CAN bus wires (should be ~60Ω with battery disconnected). Diagnosis can be performed at the central 'Star Connector' to isolate specific branches of the network. 🎬 See how to diagnose a Chrysler CAN-C star connector failure
   Typical fix: Repair the damaged section of the wiring harness or clean/replace the affected connector. Applying dielectric grease can help prevent future moisture intrusion.
   Est. part cost: $10-$200
4. Failing Brake System Control Module (ABS Module) ⚪ Low Probability While it's the module reporting the data, outright failure is less common than software or voltage issues. An internal fault can cause it to send corrupted data onto the network.
   How to confirm: This is a last resort after all other possibilities (battery, software, wiring) have been definitively ruled out by a professional using advanced diagnostic tools.
   Typical fix: Replace the ABS module and program the new module to the vehicle's VIN. This is not a plug-and-play part and requires an 'ABS Initialization' procedure with a wiTECH scan tool.
   Est. part cost: $450-$800

Rare But Worth Checking

• Faulty Wheel Speed Sensor or Wiring:
• Faulty CAN Bus Star Connector:

Diagnosis Steps

1. Check for and record any other Diagnostic Trouble Codes (DTCs) stored in any module. Note any codes related to wheel speed sensors or other 'U' codes.
2. Perform a full health check on the battery. This must include a load test to ensure it can supply adequate voltage under load (above 12.4V engine off, stable during cranking).
3. Inspect the battery terminals and primary ground connections for cleanliness and tightness. A loose connection can mimic a bad battery.
4. If the battery is healthy, contact a Chrysler dealer or specialist to check if TSB #18-013-22 is applicable and has been performed. This TSB involves a PCM software update to fix this specific code.
5. Visually inspect the wiring harness and electrical connector at the Brake System Control Module (ABS module) for any signs of corrosion, moisture, or physical damage.
6. If wiring appears intact, a professional should use an advanced scan tool (like wiTECH) to monitor the live data stream from the ABS module and check for communication errors on the CAN bus.
7. As a final step, if all other avenues are exhausted, the ABS module itself should be considered for replacement. This requires professional installation and programming.

Parts You'll Likely Need

• 12V Battery — Low system voltage is a well-documented cause of this communication code on Chrysler vehicles.
  Trusted brands: Mopar, Interstate, DieHard
  OEM price range: $250-$400
  Aftermarket price range: $150-$350
• Brake System Control Module (ABS Module) (OEM #Example Mopar Part #: 68341606AC, 68341609AC (Part numbers vary by specific vehicle options, always verify with VIN)) — This is the module that sends the 'implausible data'. It is replaced only after ruling out the more common causes like low voltage, software, and wiring issues.
  Trusted brands: Mopar
  OEM price range: $270-$620
  Aftermarket price range: $200-$500

Related Codes That Often Appear With This One

• U0403 — Implausible Data from Transfer Case Control Module, often seen together in a network communication fault scenario per TSB 18-013-22.
• U0429 — Implausible Data from Steering Column Control Module, often seen together in a network communication fault scenario per TSB 18-013-22.
• P061A — Level 2 Torque Performance, a TSB for other Chrysler models lists this code alongside U0418 as being resolved by a PCM software update.
• U11BC — Lost Brake Switch Message, another communication code listed in TSB 18-013-22 for the 2021 Chrysler 300, indicating a broader network issue.

Technical Service Bulletins (TSBs) & Recalls

• 18-013-22 - Flash: Powertrain Control Module (PCM) Updates
• 1801322 - ELECTRONIC STABILITY CONTROL
• 18-078-22 (Related Platform - Jeep Cherokee) - Explicitly notes U0418 can be set by low battery voltage.

Platform-Specific Known Issues

• A Technical Service Bulletin for the 2021 Chrysler 300 (TSB #18-013-22) lists U0418 - Implausible Data Received From Brake System Control Module 1 - alongside several other communication codes. The prescribed fix is to reprogram the Powertrain Control Module (PCM) with updated software.

Mechanic-Grade Diagnostic Values

• CAN Bus Resistance — expected: Approximately 60 Ω when measured between CAN High and CAN Low pins at a module connector with the battery disconnected.. Failure: A reading of ~120 Ω indicates a missing terminating resistor or an open in the bus. A reading significantly lower than 60 Ω (e.g., 40 Ω) suggests an extra terminating resistor or a partial short.
• CAN Bus Voltage (Key On, Engine Off) — expected: CAN High (CAN-H) should average ~2.6V, pulsing towards 3.5V. CAN Low (CAN-L) should average ~2.4V, pulsing towards 1.5V. The two signals should be mirror images of each other when viewed on an oscilloscope.. Failure: Both lines reading near 0V indicates a short to ground. Both lines reading near battery voltage indicates a short to power. Both lines reading the same voltage (e.g., 2.5V) without pulsing indicates the bus is idle or shorted together.
• System Voltage Threshold — expected: Stable voltage above 12.4V with engine off, and above 13.2V with engine running.. Failure: System voltage dropping below 10.0V, especially during startup, can cause modules to send corrupt data and erroneously trigger code U0418.

Hidden / Shadow Codes Worth Checking

• U0418-86: This is the base code with an added Failure Type Byte (FTB). The '-86' suffix specifically means 'Invalid Data'. While this aligns with the code's main definition, seeing the FTB on a dealer scan tool confirms the specific nature of the fault being received by the reporting module. (see via Typically visible on OEM-level diagnostic tools like Chrysler's wiTECH.)

Scan Tool Commands That Help

• wiTECH: ABS Initialization — This routine, found under the 'Misc Functions' tab for the ABS module, must be performed after replacing or reprogramming the ABS control module to ensure it is properly configured for the vehicle.
• wiTECH: Loss of Communication Test — This function continuously 'pings' all modules on the network. It is used to diagnose intermittent faults by allowing a technician to perform a 'wiggle test' on harnesses and connectors while watching for any module to drop off the network in real-time.
• wiTECH: View Topology — The network topology map provides a visual representation of all control modules and their communication status. Modules that are not communicating are often colored red, giving an immediate overview of which network segments or modules are offline.

Wiring & Ground Locations

• CAN Bus Star Connector (or Splice Pack) — Chrysler vehicles use a centralized star connector system. On the LX platform (300), diagnostic splice points are commonly located under the glove box area and sometimes behind the rear passenger seat trim. They serve as a junction for multiple CAN bus wires. Mopar part #68230877AA is a 'Green 13 way can connector' used on the 2021 300.. This is a critical diagnostic point. A technician can disconnect individual module branches from the star connector to isolate which part of the network is causing a fault (like a short) without having to access each module individually.
• Primary Body/Engine Grounds — Key ground points include the main battery-to-chassis ground, chassis-to-engine block ground strap (often near the transmission), and various smaller ground points on the inner fenders/shock towers.. A high-resistance or loose ground can cause a voltage drop to one or more modules, including the ABS module. This can lead to data corruption and communication codes like U0418 without any actual component failure.

Real Owner Repair Stories

• 5thGenRams Forum user (Ram 1500 (related Stellantis platform)) — Dead battery (measured 7.6V). After charging, numerous service lights appeared on the dash, including for the ABS system.
  ❌ Tried (didn't work) Clearing codes with a standard scanner., Disconnecting the battery to reset modules.
  ✅ What actually fixed it The dealer performed an 'ABS module reset' using their diagnostic tool. The deep discharge of the battery caused the module to enter a logic-locked state that required a specific scan tool command to clear.
• YouTube channel 'robthemechanic' (Ram Truck) — Complete network failure with dozens of 'lost communication' codes, but only after driving for exactly 33 miles. The truck would not shut off with the button and would reset itself after 10 minutes.
  ❌ Tried (didn't work) Visual wiring inspection., Testing individual modules.
  ✅ What actually fixed it The root cause was a failing capacitor inside the CAN bus star connector. It tested good initially but would slowly go out of spec over time, eventually corrupting the entire network. Replacing the star connector resolved the issue completely.

"I Checked Everything" — The Actual Cause

• In one documented case on a related platform, a vehicle would lose all network communication after a specific driving distance. Standard wiring and module checks revealed no faults. The actual cause was an internal failure of a capacitor within the passive CAN bus star connector, which would slowly go out of spec and corrupt the network. This type of failure is not detectable with visual inspection, continuity tests, or smoke tests and requires advanced component-level diagnostics or process of elimination by swapping the connector itself.