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Home / DTC / U0647 — Lost Communication With Motor Electronics Coolant Pump B

U0647 — Lost Communication With Motor Electronics Coolant Pump B

Detailed page for trouble code U0647.

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All codes P-codes (Powertrain) B-codes (Body) C-codes (Chassis) U-codes (Network/User) Tesla Alerts
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Code

U0647

Generic U — Network/User

Lost Communication With Motor Electronics Coolant Pump B

Brand: Generic
Type: U — Network/User
Views: UK: 15 EN: 29 RU: 16
AI status
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ready
Completed 100%
Page language: EN

Causes

  • Open or shorted wiring between PCM/module and coolant pump B
  • Poor or corroded connector(s) at the pump or module
  • Blown fuse or faulty power supply to the pump electronics
  • Bad ground at the pump electronics or control module
  • Faulty pump electronics or internal pump control module
  • CAN or LIN bus fault (low speed or high speed) interference or termination issue

Symptoms

  • MIL or coolant-related warning lamp illuminated
  • Reduced cooling performance or overheated engine message (depending on system fallback)
  • Cooling pump B not activating when commanded
  • Intermittent operation of coolant pump B
  • Related communication errors or multiple network U-codes stored
  • Possible limp-home or derate mode depending on vehicle strategy

What to check

  • Read freeze frame and stored codes; note accompanying U or P codes
  • Attempt to communicate with coolant pump B module using a scan tool
  • Visually inspect connectors and wiring at the coolant pump and control module for damage, corrosion, or water intrusion
  • Check fuses and relays related to coolant pump power
  • Backprobe pump connector for battery voltage with ignition on and while commanding pump on
  • Check ground integrity at pump and control modules (measure resistance to chassis)

Signal parameters

  • Module present/response to OBD-II/diagnostic scanner queries (yes/no)
  • CAN bus idle voltages at connector: CAN_H and CAN_L ~ nominal mid-rail (verify against OEM data)
  • Differential CAN voltage on active communication (dominant state present during bus activity)
  • Supply voltage to pump electronics with ignition ON and during commanded run (approx. battery voltage)
  • Ground continuity from pump module to chassis (< a few ohms)
  • Control/command message frequency from PCM to pump module (messages present or missing)

Diagnostic algorithm

  1. Confirm U0647 is current and note if condition is intermittent or permanent.
  2. Check for and record any additional DTCs (especially other U-codes or powertrain codes) that could point to a shared wiring or bus issue.
  3. Visually inspect connectors, pins and wiring at the coolant pump B and any gateway/module; repair any physical damage or corrosion.
  4. Verify fuses/relays for pump power; replace if blown and investigate cause.
  5. With a scan tool, attempt to communicate with the pump module. If no communication, backprobe the pump connector: verify battery voltage on the supply pin, and a good ground on the ground pin.
  6. Measure CAN_H and CAN_L (or LIN if used) at the pump connector and at a known-good module; compare voltages and look for open, short to battery/ground, or missing termination.
  7. If power/ground and bus look good but module still fails to communicate, check for intermittent faults by wiggling harnesses while monitoring communication and codes.
  8. If wiring, power and bus integrity are confirmed, consider bench-testing or substituting a known-good pump/module per OEM procedure before replacement.
  9. After repairs, clear codes and perform a drive or functional test to confirm fault does not return and pump operates as commanded.
  10. If the code returns, capture live data and consult OEM wiring diagrams and module software updates before replacing modules.

Likely causes

  • Loose/corroded connector at coolant pump B
  • Open/short in the pump power/ground or communication wires
  • Blown fuse or lost supply to the pump electronics
  • Faulty pump control module (after verifying wiring and power)
  • CAN bus wiring/termination problem between modules

Fault status

⚠️ Status
Communication to Motor Electronics Coolant Pump B not detected. Check wiring, power/ground and CAN/LIN network before replacing the pump module.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

U0100 U0121 U0126 U0140 U0155
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