Diagnostic guide for OBD-II code U0128

Lost Communication with Park Brake Control Module (PBCM)

Scope and meaning

• U0128 is a network communication code in the U (body/network) family. In many vehicle implementations, it specifically indicates Lost Communication with the Park Brake Control Module (PBCM). This means the vehicle's scan tool or on-board diagnostics detected that the PBCM is not communicating reliably on the vehicle's data network. This interpretation aligns with standard OBD-II definitions and is commonly described in general OBD references (e.g., OBD-II diagnostic code overviews) and real-world reports. For reference, OBD-II diagnostic code discussions describe U codes as network communication codes in the broader DTC framework ( A real-world user report also confirms the U0128 fault involving a park brake control module on a Honda.

• Vehicle context: The Park Brake Control Module (PBCM) is part of the electronic parking brake system. In many vehicles, the PBCM communicates with other controllers (such as the vehicle's ECU, ABS module, instrument cluster, etc.) over a data network (commonly CAN bus). When the PBCM stops communicating, the U0128 code is typically logged.

Real-World Symptoms

• The most directly reported symptom in the verified NHTSA complainant is a brake-related concern associated with a lost communication with the park brake control module in a Honda. This aligns with the code name and commonly observed symptom patterns (warning lights, parking brake behavior, etc.) when network communication to the PBCM is interrupted.

• Other brake system symptoms may appear or be related only indirectly when a diagnostic code is present, such as warning lights or intermittent parking brake function, depending on the vehicle and how its body network handles the fault.

System overview (what to check)

• Park Brake Control Module (PBCM): the central module in the parking brake system that can be on the data network. A communication fault to/from this module is what U0128 indicates.
• Data network: the vehicle's CAN bus or other vehicle networks that carry messages between the PBCM and other controllers (ECU, ABS, instrument cluster, etc.).
• Related power/ground: the PBCM's power and grounding circuits, and the ignition feed, since loss of power or poor grounding can mimic or cause communication faults.
• Connectors and wiring: harness connectors, pin integrity, corrosion, damaged insulation, and any recent service that disturbed the network.
• Software/firmware: possible need for software reflash or calibration alignment if the network has become desynchronized or if the PBCM software is out of date.

Probable Causes

Note: The NHTSA data available for this code is limited (one relevant complaint). As a result, probability percentages below are provided as a cautious, illustrative guide rather than statistically robust figures. See the "Data caveats" note at the end.

• PBCM fault or failure (hardware/software): 40-60%

• CAN bus/wiring issue (open/short, damaged harness, loose connectors): 20-40%

• Power/ground or ignition feed issue to PBCM: 10-20%

• Software/firmware mismatch or need for reflash: 5-15%

• Other module communication issues or system integration faults: 5-10%

• Data caveat: With only one NHTSA complaint in the verified set specifically referencing U0128 with a Honda PBCM, these probabilities are not statistically robust. They reflect typical engineering considerations for CAN-network U-codes and observed patterns, not a definitive distribution. If more NHTSA data becomes available, revisit these estimates.

Diagnostic Approach

Safety Considerations

1) Confirm and scope the problem

• Use a capable OBD-II scan tool to confirm U0128 and note any other U-codes or P-codes present.
• Check freeze-frame data and any data stream related to the PBCM's expected communications (if your tool provides network/node status, look for missing nodes or absent CAN messages).

2) Gather context and related codes

• Look for other modules that may have lost communication (ABS, PCM, Instrument Cluster, BCM, etc.). A cluster of U-codes or a pattern of missing modules often indicates a network or bus issue rather than a single module failure.

3) Visual inspection and basic electrical checks

• Inspect PBCM connectors and wiring harness for signs of moisture, corrosion, bent pins, or loose connectors.
• Check for any recent service that could have disturbed the park brake wiring or CAN wiring.
• Check fuses and relays related to the PBCM power/ignition feeds and grounds.
• Inspect ground connections to the PBCM and chassis/frame grounds used by the data network.

4) Power, ground, and ignition supply to PBCM

• Verify that the PBCM receives proper battery voltage with ignition ON and with engine RUN if applicable to the vehicle. Note any voltage drops or intermittent voltage.
• Check for a solid ground path to the PBCM. A high resistance ground can cause communication issues.

5) Data network (CAN) verification

• If possible, measure CAN High and CAN Low resistance when the vehicle is off and on, and inspect for shorts to power or ground.
• Use the scan tool to monitor live CAN bus activity and confirm if any nodes (ECUs) are failing to present or acknowledge messages to the PBCM.
• Look for bus contention or excessive error frames if your tool supports CAN diagnostics.

6) Isolate the issue to PBCM vs. network

• If power and ground check out, and wiring/connectors look clean, and other nodes are visible on the CAN network but the PBCM remains non-responsive, consider the likelihood of a PBCM fault.
• If you can access a known-good PBCM (or a compatible replacement), and the system begins to communicate, this strongly points to a PBCM fault or the need for programming.

7) Software/firmware considerations

• Check for any available vehicle-specific software/firmware updates or service bulletins related to the PBCM or parking brake system.
• If the vehicle supports reflash or reprogramming, consider updating the PBCM software if you determine the fault is software-related or if there is a known bulletin addressing U0128 for this model.

8) Repair considerations based on findings

• PBCM fault: Replace or reprogram the PBCM as per manufacturer guidelines. After replacement or reflash, perform any required initialization/learning procedures for the parking brake system if specified by the OEM.
• Wiring/harness issue: Repair or replace damaged wiring or connectors; ensure all harness routing is correct and secure; reseal connections to prevent moisture intrusion.
• Power/ground issue: Repair the power or ground circuit as needed; replace faulty fuses/relays if found defective.
• Intermittent network/TPMS/other module issues: Address root cause on the related module or perform necessary software updates; clear codes and recheck.

9) Re-test and verification after repair

• Clear U0128 and drive the vehicle through typical operating cycles, including parking brake engagement/disengagement if applicable, to verify that the code does not return.
• Re-scan after a full drive cycle to ensure the fault is resolved and no new codes have appeared.
• Confirm the PBCM is communicating reliably with other modules on the network.

10) Documentation

• Record all findings: routes checked, measurements taken (power, ground, CAN continuity), wiring condition, connector condition, any fault codes observed before/after repair, the repair performed, and the verification drive results.

11) Follow-up actions

• If the problem recurs, escalate to OEM service procedures or a recall/TSB lookup for the model/year to determine if there are known issues with the PBCM or related network components. NHTSA complaint patterns sometimes indicate recurring service issues or vendor-specific problems, but the data here is limited (see data caveat below).

What to check and collect during testing

• Vehicle model/year and exact PBCM location
• All active DTCs (U-codes and P-codes)
• Freeze-frame data
• Module IDs and CAN bus topology if your tool provides it
• Power/voltage readings on PBCM supply and ground pins
• CAN High and CAN Low continuity readings
• Physical condition of PBCM connectors and harness

Safety Considerations

• Work with the vehicle in a well-ventilated, well-lit area; apply safety procedures when interacting with brake systems.
• Ensure the parking brake is disengaged or secured safely during diagnostic work; follow OEM procedures for parking brake system service.
• Disconnect power only as needed per OEM guidelines to avoid electrical shorts or system damage.
• Be cautious of high-voltage or special equipment requirements if working on certain vehicle architectures.

Data sources and context notes

• NHTSA real-world complaints provide real-world context that U0128 can appear in brake-related complaints where the PBCM communication is lost (Complaint: "LOST COMMUNICATION WITH PARK BRAKE CONTROL MODULE" on a Honda). This illustrates a plausible scenario, though it is a single data point and should be treated as a case example rather than a statistical average.
• General OBD-II code structure and the concept of U-codes (network communications) are described in the OBD-II diagnostic code literature. In particular, the Wikipedia OBD-II article discusses Diagnostic Trouble Codes and the nature of network (U) codes as part of the DTC framework.
• The Park Brake Control Module and its network implications are informed by general knowledge of how vehicle networked modules operate and the common practice of diagnosing U0128 as a network communication issue with the PBCM. See the same OBD-II DTC discussions for context on how U-codes signify communication problems.

Notes on probability guidance

• Because there is only a single NHTSA complaint set specifically mentioning U0128 with a Park Brake Control Module in a Honda, the probability estimates for root causes are not statistically robust. The numbers provided above are indicative of typical failure modes in network-based U-codes and reflect common automotive diagnostic reasoning rather than a proven distribution. If more NHTSA data or manufacturer service data becomes available, revisit these likelihood estimates.

This diagnostic guide was generated using verified reference data:

• NHTSA Consumer Complaints: 1 real-world reports analyzed
• Wikipedia Technical Articles: OBD-II

Content synthesized from these sources to provide accurate, real-world diagnostic guidance.

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