U0594 on 2021 Dodge Challenger: Implausible HCP Data Explained

What's Unique About the 2021-2021 Dodge CHALLENGER

It is critical to know that the 2021 Dodge Challenger is not a hybrid vehicle. Many generic online resources incorrectly define U0594 as an issue with a 'Hybrid Control Processor'. On the Challenger and its platform mates (Dodge Charger, Chrysler 300), 'HCP' refers to a processor within the braking system. The presence of a specific Technical Service Bulletin (TSB #18-011-22) for this model groups U0594 with other brake and stability control communication codes, confirming the issue lies within the chassis control system, not a non-existent hybrid powertrain.

Diagnostic Flowchart

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

Symptoms You May Notice

• Illumination of the ABS warning light.
• Illumination of the Electronic Stability Control (ESC) or traction control warning light.
• A 'Service ABS System' or 'Service Electronic Stability Control' message on the instrument cluster display.
• Loss of cruise control functionality.
• In some related cases, the power steering may feel heavy or lock as it is also tied into the vehicle's network.

Most Likely Causes

1. Brake System Control Module Software Fault 🔴 High Probability A manufacturer-issued TSB (#18-011-22) exists that groups U0594 with a wide array of other communication codes, which strongly suggests a known software logic issue that can be resolved with an update. This is the most common first-step repair performed by dealerships.
   How to confirm: A dealer or qualified shop must use a wiTECH scan tool to check the current software calibration of the Brake System Control Module (also called ABS module) against the latest available version in the DealerCONNECT service library.
   Typical fix: Reprogramming (flashing) the Brake System Control Module with the updated software provided by the manufacturer. A battery charger must be connected during the flash process to ensure stable voltage.
   Est. part cost: $0
2. Faulty Anti-Lock Brake System (ABS) Module 🟡 Medium Probability The HCP is an internal part of the ABS module. An internal hardware failure of the module can cause it to send implausible data, triggering this code. This becomes the primary suspect if a software flash does not resolve the issue.
   How to confirm: If the module's software is confirmed to be up-to-date and all wiring/power/grounds are verified as good, the fault is isolated to the module itself by process of elimination.
   Typical fix: Replacement of the electronic portion of the ABS module. 🎬 See this walkthrough on replacing the module to fix ABS lights In many cases, just the electronic controller can be unbolted from the hydraulic pump, avoiding the need to open brake lines and bleed the system. The new module must then be programmed to the vehicle's VIN and an initialization or 'Proxy Alignment' procedure must be performed.
   Est. part cost: $250-$800
3. Wiring or Connector Issue ⚪ Low Probability While less common than module faults, issues can still arise. A Reddit user with similar network codes on a Challenger traced a persistent battery drain and ABS/ESC lights to a faulty ground connector for the ABS module causing it to stay powered on.
   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 multimeter can be used to check for continuity and proper voltage/ground on the CAN bus and power lines.
   Typical fix: Repairing the damaged section of the wiring harness or cleaning/replacing the faulty connector. Ensure ground connections are clean and tight.
   Est. part cost: $20-$100

Rare But Worth Checking

• Low Battery Voltage:

Diagnosis Steps

1. Connect a high-level bidirectional scan tool (like Autel MK808S or Mopar wiTECH) capable of reading manufacturer-specific codes from all vehicle modules.
2. Check for and document all stored Diagnostic Trouble Codes (DTCs). Note if U0594 appears with other codes mentioned in TSB #18-011-22 (e.g., U0429, U0432, U110A).
3. Check for applicable Technical Service Bulletins for the vehicle's VIN. Specifically look for TSB #18-011-22.
4. If TSB #18-011-22 applies, use a dealer-level tool (wiTECH) to verify the current software version of the Brake System Control Module and reprogram it if an update is available. Ensure a stable power supply (battery charger) is used during the flash.
5. If no software update is available or the issue persists, perform a thorough visual inspection of the ABS module connector and its wiring harness 🎬 Watch: Locate the ABS module and pump on your Challenger for any signs of physical damage, corrosion, or water intrusion.
6. Using a multimeter, verify the ABS module has proper power and ground. A faulty ground connection has been noted by owners as a cause for similar issues.
7. If wiring and software are confirmed good, the fault is most likely internal to the ABS module. The module will need to be replaced.
8. If replacing the module, it is often possible to replace only the electronic part without opening hydraulic lines. The new module must be programmed to the car's VIN and an ABS initialization procedure must be performed.
9. After any repair, clear all DTCs and perform a test drive, including turning the steering wheel, to ensure the fault does not return and all systems re-initialize.

Parts You'll Likely Need

• Anti-Lock Brake System (ABS) Module (OEM #68399772AG (supercedes 68399772AF), 68258644AA) — If a software reflash does not fix the issue, the HCP's internal fault requires the replacement of the entire ABS module it is housed in. Part number can be VIN specific.
  Trusted brands: Mopar
  OEM price range: $250-$600
  Aftermarket price range: $200-$450

Related Codes That Often Appear With This One

• U0429 — Implausible Data Received From Steering Column Control Module (SCM). This code is listed in the same TSB and indicates a wider network communication issue, often originating from the ABS module software fault.
• U0432 — Invalid Data Received From Multi-Axis Acceleration Sensor Module. Also listed in TSB #18-011-22, pointing to a fault in the stability control system data, which is processed by the ABS module.
• U110A — Lost Communication With SCM. This further reinforces that the issue is network-related, often stemming from a single module or software glitch causing a cascade of codes.
• C2200 — Anti-Lock Brake Module Internal. This is a more direct code indicating an internal failure of the ABS module and is often seen in conjunction with network communication faults when the module itself is the root cause.

Technical Service Bulletins (TSBs) & Recalls

• 18-011-22: A TSB for 2021 Dodge Challengers (and other models) built on or before Oct 14, 2021. It addresses a MIL illumination with a host of 'U' codes, including U0594, U0429, and U0432. The prescribed fix is to reprogram the PCM with the latest software.

Platform-Specific Known Issues

• A known software issue documented in TSB #18-011-22 can cause this code to appear along with a cluster of other network communication faults related to the chassis control system. This TSB is the primary reason a software reflash is the first recommended repair step.
• The term 'HCP' is specific to the internal architecture of the braking module on this platform and should not be confused with 'Hybrid Control Processor' as seen on vehicles like the Chrysler Pacifica Hybrid.

Mechanic-Grade Diagnostic Values

• CAN C Bus Resistance — expected: ~60 Ohms. Failure: A reading of ~120 Ohms indicates a missing termination resistor or an open in the bus. A reading significantly lower than 60 Ohms (e.g., 40 Ohms) could indicate a shorted module or extra resistor on the network. An infinite reading indicates an open circuit.
• CAN C Bus Voltage (Key On, Engine Off) — expected: CAN High (CAN C +): ~2.5V to 3.5V. CAN Low (CAN C -): ~1.5V to 2.5V. Both lines should mirror each other around a 2.5V bias.. Failure: Voltages stuck high or low, or a line that is stuck at 0V or battery voltage, indicates a short to power or ground. If both lines read the same static voltage (e.g., 2.6V), the bus may be idle or a module may be pulling it down.

Scan Tool Commands That Help

• wiTECH or equivalent (Autel, Appcar DiagFCA): Proxy Alignment (Proxi Configuration) — This procedure is mandatory after replacing the ABS module. It synchronizes the new module with the vehicle's Body Control Module (BCM) and other ECUs on the network. Failure to perform a Proxy Alignment will result in a flashing odometer and persistent communication fault codes.
• wiTECH or equivalent: ABS Initialization — After replacing and performing a proxy alignment on a new ABS module, this routine must be run. It typically involves a short test drive with specific maneuvers (like a 90-degree turn) to calibrate the steering angle and yaw rate sensors, which are critical for the ESC system.

Wiring & Ground Locations

• Anti-Lock Brakes Module — In the engine compartment, on the driver's side, next to the windshield washer fluid reservoir.. This is the physical location of the module that sets the U0594 code. The main electrical connector here is a primary point of inspection for corrosion or damage.
• G100 — Left front of the engine compartment.. This is a major chassis ground point. While not exclusively for the ABS module, a poor connection at this ground can cause a variety of electrical issues, including communication faults on the CAN bus.
• ABS Module Connector C1 — The main electrical plug on the ABS module itself.. The CAN C bus wires run through this connector. For a 2021 model, based on similar schematics, the CAN C (+) is typically a White/Light Blue wire and CAN C (-) is a White/Black wire. Verifying voltage and resistance at these pins is a key diagnostic step.

Real Owner Repair Stories

• r/Challenger on Reddit (2016 Dodge Challenger) — ABS light on, 'Service Electronic Stability Control' message, heavy/locked steering, and a constant battery drain.
  ❌ Tried (didn't work) Replacing all ABS sensors.
  ✅ What actually fixed it The user did not post a final fix, but another user provided a highly relevant diagnosis: 'This very much sounds like a can bus problem (can c specifically) which would also explain the battery draw…if the BCM can't communicate that the ign is off to one or more controllers they won't power down or may wake repeatedly.' This points to a network fault (like U0594) causing other modules to stay active and drain the battery, a classic symptom missed by basic diagnosis.

OEM Part Supersession History

• 68399772AA, AB, AC, AD, AE, AF → 68399772AG — Manufacturer revision to improve reliability or address known faults.
  Heads up: The latest part number, 68399772AG, is the correct service replacement for all previous versions for this vehicle range. Using an older, used part may re-introduce the original fault.

Model Year Variations Within This Range

• 2021: TSB #18-011-22, which addresses a software fix for U0594 and other codes, specifically applies to vehicles built on or before October 14, 2021. Vehicles built after this date should already have the updated software from the factory, making a software issue less likely and pointing more towards a hardware failure if this code appears.