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Home / DTC / B0423 — Body Control Module (BCM) CAN Bus Communication Error

B0423 — Body Control Module (BCM) CAN Bus Communication Error

Detailed page for trouble code B0423.

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Code

B0423

HUMMER B — Body

Body Control Module (BCM) CAN Bus Communication Error

Brand: HUMMER
Type: B — Body
Views: UK: 19 EN: 26 RU: 24
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Page language: EN

Causes

  • Open or shorted CAN_H or CAN_L wiring (to power, ground or each other)
  • Poor connector pin contact, corrosion, or damaged BCM connector
  • Missing or incorrect bus termination (open or high-resistance terminations)
  • Another module on the CAN bus is driving the bus incorrectly or has failed
  • Low battery voltage or intermittent supply/ground to BCM
  • Intermittent wiring (chafing, water intrusion) or failed splice/ground

Symptoms

  • Multiple body electrical features inoperative or intermittent (locks, lights, wipers, etc.)
  • Illuminated dash warnings for communication or multiple modules
  • Intermittent or no diagnostic data from BCM on scan tool
  • Other modules report loss-of-communication DTCs
  • Possible vehicle no-start if powertrain messages are affected

What to check

  • Retrieve all stored and pending DTCs from all modules — note time stamps and freeze-frame data
  • Confirm battery voltage is stable (12.4 V+ at rest, >13 V while cranking/charging)
  • Visually inspect BCM and CAN harness connectors for corrosion, bent pins, water intrusion, or mechanical damage
  • Check for additional communication codes in other modules (U0xxx series) to identify affected bus segment
  • Measure CAN_H and CAN_L idle voltages at BCM connector with DVOM or lab scope (see signal parameters)
  • Measure bus termination resistance between CAN_H and CAN_L with ignition off (~60 ohms typical)

Signal parameters

  • CAN bus recessive (idle) voltages: CAN_H ≈ 2.5–3.5 V, CAN_L ≈ 1.5–2.5 V (both near 2.5 V typical)
  • CAN dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2 V)
  • Differential voltage active ≈ 1.5–3.0 V during data bits (varies by transceiver)
  • Bus termination resistance (between CAN_H and CAN_L) ≈ 60 ohms (two 120-ohm terminators in parallel)
  • Common bus speeds: 250 kb/s or 500 kb/s depending on model — confirm exact rate in service manual
  • Expected periodic BCM CAN frames/messages visible with scan tool or scope when healthy (message IDs vary by model)

Diagnostic algorithm

  1. Connect a capable scan tool and record all communication-related codes from all modules. Note which bus (low-speed body, high-speed powertrain) is referenced.
  2. Verify vehicle battery and charging system health. Restore proper battery voltage before continuing diagnostics.
  3. Visually inspect BCM connector, harness routing, splices, and grounds for damage or corrosion. Repair any obvious issues.
  4. With ignition ON, measure CAN_H and CAN_L voltages at the BCM connector. Compare to expected signal parameters. Use an oscilloscope to view differential signal if available.
  5. With ignition off, measure resistance between CAN_H and CAN_L at the BCM — confirm approx 60 ohms. If open or high, inspect termination and end-of-line connectors.
  6. Perform wiggle/connect/disconnect tests on BCM connector and nearby harness while monitoring for DTC change or restored bus traffic. Do not backprobe a live airbag connector or other safety device.
  7. If a single external module is suspected, disconnect that module per OEM procedure and observe whether B0423 clears and bus behavior returns to normal.
  8. If wiring and connectors check good, consider module-level fault: reseat BCM, check for software updates, and follow OEM procedure for BCM reprogramming or replacement. Confirm replacement module is programmed and coded correctly.
  9. After repairs, clear codes and perform a road/operation cycle to confirm fault does not return. Re-scan all modules for secondary DTCs.

Likely causes

  • Corroded or pushed-out pins at BCM connector or splice
  • Shorted CAN wire to battery or ground due to chafed harness
  • Failed module elsewhere on same CAN segment pulling bus dominant
  • Open or high-resistance termination resistor or disconnected end-of-line connector
  • Weak battery or poor ground/ignition supply to BCM causing intermittent comms

Fault status

⚠️ Status
Body Control Module reports CAN bus communication error — expected CAN messages not received or abnormal bus conditions detected.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

U0073 U0100 U0121 U0140 U0155 B0414
Repair manuals

Manual library for HUMMER

138

Browse 138 HUMMER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

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