U0594 on 2021 Chrysler 300: Causes of ABS/Brake System Communication Faults

What's Unique About the 2021-2021 Chrysler 300

The key challenge with U0594 on a Chrysler 300 is its dual meaning within the manufacturer's ecosystem. While it's a well-documented hybrid powertrain code on PHEVs like the Pacifica and Wrangler, its appearance on the non-hybrid 300 is specific and rare. The authoritative TSB #1801322 firmly places it in the context of the Electronic Stability Control and Brake System, not a non-existent hybrid system. This ambiguity means mechanics must ignore the common 'hybrid' definition and focus diagnostics entirely on the ABS and network systems specific to the 300 platform, likely related to the ABS pump motor circuit.

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 (ESC/ESP) warning light illuminated
• Brake warning light may be on
• Potential messages on the instrument cluster regarding service to the brake or stability system
🎬 Watch: Why your ABS and brake lights are staying on

Most Likely Causes

1. Brake System Control Module (ABS Module) Internal Fault 🔴 High Probability → Shop ABS Control Module The TSB #1801322 lists U0594 alongside other data codes originating from the brake system. On the related Dodge platform, this code is specifically tied to a 'Pump Motor Circuit Malfunction', indicating a failure within the ABS module or its integrated pump. These modules are a known failure point on the LD platform.
   How to confirm: After ruling out wiring and software, a technician using a dealer-level scan tool (like wiTECH) can test the ABS pump and module functions. Failure to communicate or persistent data errors point to an internal fault. Replacement requires VIN-programming and a 'Proxy Alignment' procedure.
   Typical fix: Replacement of the ABS module/pump assembly, followed by programming and calibration. 🎬 See this time-saving trick for replacing the ABS module
   Est. part cost: $400-$800
2. Software Glitch / Corrupted Firmware 🟡 Medium Probability Modern vehicle modules are complex computers, and software anomalies can cause communication errors. Chrysler frequently issues software updates to fix such issues across its lineup.
   How to confirm: A dealership or qualified shop can check the current software calibration of the Brake System Control Module against the latest version available from Chrysler using a tool like wiTECH.
   Typical fix: Reprogramming (flashing) the module with the latest software.
   Est. part cost: $0-$200
3. Wiring or Connector Issue 🟡 Medium Probability The wiring harness to the ABS module is located in the engine bay and can be exposed to moisture, heat, and vibration, potentially leading to corrosion, loose pins, or high resistance in a ground connection.
   How to confirm: Visually inspect the wiring harness and connector at the ABS module. A multimeter is used to test for proper power, ground, and CAN bus network continuity. A common, but often overlooked, step is to check the chassis ground point for the ABS module for corrosion or high resistance.
   Typical fix: Repairing the damaged wire, cleaning/tightening ground connections, or cleaning/replacing the connector.
   Est. part cost: $10-$150
4. Weak or Failing 12V Battery ⚪ Low Probability → Shop Vehicle Battery Like many modern cars, the Chrysler 300's various electronic modules are sensitive to low voltage. A weak battery can cause modules to drop off the communication network or send corrupt data during startup, generating spurious fault codes. Owners on forums report that a failing battery can cause a host of seemingly unrelated electronic issues.
   How to confirm: Test the battery with a multimeter (should be >12.4V engine off) and, more importantly, have it load-tested to confirm its health. Slow engine cranking is a key symptom.
   Typical fix: Recharge or replace the 12V battery.
   Est. part cost: $150-$300

Diagnosis Steps

1. Connect a high-level OBD-II scanner capable of reading manufacturer-specific codes from all modules (ABS, BCM, PCM, etc.).
2. Document U0594 and all other active or stored codes. Note which modules are reporting faults.
3. Test the 12V battery's voltage and perform a load test to rule out low voltage as a cause.
4. Inspect all fuses related to the ABS and stability control systems.
5. Locate the ABS module in the engine bay. Carefully inspect its main electrical connector and the surrounding wiring for any signs of corrosion, moisture intrusion, or physical damage.
6. Using a wiring diagram, test the power and ground circuits at the ABS module connector. Specifically check for high resistance at the chassis ground points for the module.
7. If wiring, power, and ground are good, use an advanced scan tool (e.g., wiTECH) to check for the latest software updates for the Brake System Control Module and other related modules.
8. If no software updates are available and all wiring is confirmed good, the ABS module itself is the most likely culprit.
9. If replacing the module, a 'Proxy Alignment' procedure is required using a tool like wiTECH to integrate the new module with the vehicle network.
🎬 Watch: Step-by-step guide to performing a Proxi Alignment

Parts You'll Likely Need

• ABS Control Module / Hydraulic Unit (OEM #e.g., 68500121AC (Note: Part number is VIN-specific and depends on options like Adaptive Cruise Control)) — This module is the central computer for the ABS and stability systems. An internal failure, either in the electronics or the pump motor circuit, can cause it to send corrupt data, triggering the U0594 code. The part number is highly dependent on whether the vehicle is equipped with Adaptive Cruise Control (ACC); ensure the replacement part matches the vehicle's configuration.
  Trusted brands: Mopar
  OEM price range: $600-$900
  Aftermarket price range: $300-$600

Related Codes That Often Appear With This One

• U0429 — Implausible Data Received From Steering Column Control Module (SCM). Listed in the same TSB #1801322, indicating a wider network communication issue.
• U0432 — Invalid Data Received From Multi-Axis Acceleration Sensor Module. Listed in the same TSB #1801322, related to the stability control system.
• U110A — Lost Communication With SCM. Listed in the same TSB #1801322, pointing to a network fault.
• U1110 — Lost Vehicle Speed Message. Listed in the same TSB #1801322, a critical data point for the ABS module.

Technical Service Bulletins (TSBs) & Recalls

• 1801322: A 2022 TSB for the 2021 Chrysler 300 that lists U0594 in conjunction with other codes related to the Electronic Stability Control and Brake System Control Module.

Platform-Specific Known Issues

• Misleading 'HCP' Acronym: The primary vehicle-specific issue is the code's definition, 'Implausible Data Received From HCP'. 'HCP' is used for 'Hybrid Control Processor' on other Chrysler products like the Pacifica PHEV, which does not exist on the 300. This causes significant diagnostic confusion, requiring the technician to know that on this platform, the fault lies within the ABS/Brake Control Module.

Mechanic-Grade Diagnostic Values

• CAN C Bus Resistance — expected: Approximately 60 Ω between CAN C (+) and CAN C (-) pins at the ABS module connector (with battery disconnected).. Failure: A reading of ~120 Ω indicates a missing terminating resistor or an open circuit. A reading near 0 Ω indicates a short circuit between the two CAN lines.
• CAN C Bus Voltage (Key On, Engine Off) — expected: CAN High (C+) should be ~2.5-3.5V. CAN Low (C-) should be ~1.5-2.5V. Both signals should mirror each other when viewed on an oscilloscope.. Failure: Voltages stuck high, low, or near 0V indicate a short to power, short to ground, or an open circuit. A bias voltage not resting near 2.5V points to a network problem.
• ABS Module Power Supply — expected: Battery voltage (approx. 12.6V with engine off) at the specified power input pins on the ABS module connector.. Failure: Low or no voltage indicates a blown fuse, fusible link, or an open in the power supply wire.
• ABS Module Ground Circuit Resistance — expected: Less than 1.0 Ω between the ground pins on the ABS module connector and a clean chassis ground point.. Failure: High resistance (anything over 1.0-2.0 Ω) indicates a corroded or loose ground connection, which can cause intermittent communication faults.

Scan Tool Commands That Help

• wiTECH: ABS Initialization — This routine must be performed after replacing the ABS module or flashing its software. It calibrates sensors and ensures the module is correctly configured for the vehicle.
• wiTECH: Proxy Alignment (Proxi Configuration) — Required any time a major network module like the ABS unit is replaced. This function updates the vehicle's central configuration file, stored in the BCM, to recognize the new module and allow it to communicate properly on the network.
• wiTECH: ABS Pump Motor Activation — This is a bidirectional test used to command the ABS pump motor to run. It directly verifies the integrity of the pump motor and its power/ground circuits, which is highly relevant given the 'Pump Motor Circuit Malfunction' definition on related platforms.
• wiTECH: View Network Topology — This screen provides a visual map of all vehicle modules and their communication status. It can quickly show if the ABS module (and others) is not responding (colored red), helping to isolate a network-wide problem from a single module failure.

Wiring & Ground Locations

• Star Connector (CAN C Diagnostic Connector) — On the Chrysler 300, the Star Connector is typically located under/behind the glovebox. The glovebox may need to be removed and carpet pulled back to access it.. The Star Connector is the central hub where the CAN C bus wires from various modules meet. It provides a single point to test the entire network's resistance and voltage, or to disconnect branches of the network to isolate a faulty module or wire that is bringing the whole bus down.
• ABS Module Ground — Typically located on the frame rail in the engine compartment, very close to the ABS hydraulic unit. It will be a wire bolted directly to the chassis.. A poor ground connection is a very common cause of intermittent electronic module faults, including communication codes like U0594. High resistance at this point can cause the module to power up incorrectly or send corrupt data.
• ABS Module Fuses — In the front fuse box (Power Distribution Center) located in the engine compartment. For a 2021 model, check fuses F05 and F06, as well as F36 and F39.. The ABS module has multiple power feeds for the control electronics and the high-current pump motor. A blown fuse will cause a loss of communication or function, directly leading to fault codes.