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Home / DTC / U027A — Lost Communication With Battery Charger Control Module C

U027A — Lost Communication With Battery Charger Control Module C

Detailed page for trouble code U027A.

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U027A

Generic U — Network/User

Lost Communication With Battery Charger Control Module C

Brand: Generic
Type: U — Network/User
Views: UK: 17 EN: 19 RU: 9
AI status
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Page language: EN

Causes

  • Battery Charger Control Module C fault
  • Damaged or disconnected CAN/LIN wiring or connectors
  • Blown fuse or supplied power/ground loss at the charger module
  • CAN/LIN bus short to battery or ground, or open circuit
  • Corroded or loose connectors at the module or junctions
  • Incorrect or missing bus termination resistors

Symptoms

  • No live data from Battery Charger Control Module C on scan tool
  • Charging system warning lamp or message on dash
  • Battery not charging properly or limited charging functions
  • Other network modules reporting related U-codes or “bus off” conditions
  • Intermittent or complete loss of functions tied to the charger module

What to check

  • Read and record all U-codes and freeze-frame with a capable scan tool
  • Verify battery voltage (should be ~12.4–12.9 V at rest, >11 V cranking)
  • Inspect fuses and fusible links supplying the charger module
  • Visually inspect connectors and wiring for damage, corrosion, or loose pins
  • Check for presence of module in vehicle network list (scan tool)
  • Backprobe module power and ground circuits for proper voltage and continuity

Signal parameters

  • CAN idle (recessive) voltages: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (vehicle-dependent)
  • CAN dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V; differential ≈ 2 V
  • Typical bus termination: ~60 Ω measured between CAN_H and CAN_L (two 120 Ω in parallel)
  • Common CAN data rates: 125 kbps, 250 kbps, 500 kbps (verify vehicle-specific)
  • Module supply voltage: battery voltage present at module power terminal (approx. 12 V)
  • Ground circuit: near 0 V with good continuity to chassis

Diagnostic algorithm

  1. Connect a scan tool that can display network modules; record all active and stored U-codes and freeze frame data.
  2. Verify battery state and recharge if low. Low battery can prevent modules from waking.
  3. Clear the code and attempt to communicate with the charger module. If code returns, proceed with wiring/communication checks.
  4. Inspect fuses and power/ground at the battery charger control module connector. Repair any open circuits.
  5. Visually inspect connectors and harness from module to gateway for damage or corrosion. Repair or secure connectors as needed.
  6. Backprobe module power and ground with key ON; verify correct voltages and good ground.
  7. With key ON, measure CAN_H and CAN_L at the module connector and at a known-good module location. Compare voltages and look for lack of activity or incorrect levels.
  8. Measure termination resistance across CAN_H–CAN_L with battery disconnected; expect ~60 Ω. If open or very low, trace and repair the bus.
  9. Use a scope or high-speed CAN tester to check for correct differential waveforms and noise; isolate sections of the bus to find a shorted or noisy segment.
  10. If wiring and bus are good but communication still lost, swap or bench-test the battery charger control module if a known-good unit is available. Reprogram or update module software if required by manufacturer.
  11. After repair or replacement, clear codes, verify communication restored, and perform charging system function test and road test as required.

Likely causes

  • Connector corrosion or pin damage at the charger control module
  • Open/short in CAN_H or CAN_L between module and gateway
  • Blown fuse or removed battery supply to the charger control module
  • Faulty battery charger control module hardware or failed MCU
  • Improper termination (missing 120 Ω resistors) or low battery voltage preventing module wake

Fault status

⚠️ Status
Lost communication with Battery Charger Control Module C — no network messages received from module.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1-3 hours (varies by vehicle design and access)

Similar codes

U0100 U0073 U0121 U0140 U0101 U0293
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