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Home / DTC / U0648 — Lost Communication With Motor Electronics Coolant Pump C

U0648 — Lost Communication With Motor Electronics Coolant Pump C

Detailed page for trouble code U0648.

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U0648

Generic U — Network/User

Lost Communication With Motor Electronics Coolant Pump C

Brand: Generic
Type: U — Network/User
Views: UK: 14 EN: 29 RU: 13
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Page language: EN

Causes

  • Open or short in CAN bus wiring (CAN High or CAN Low)
  • Faulty connector or corroded terminals at the pump module or wiring harness
  • Failed Motor Electronics Coolant Pump C module or internal electronic fault
  • Loss of power or ground to the pump control module
  • Network termination or bus resistance incorrect (missing/failed terminator)
  • Intermittent wiring or pin damage from chafing or water intrusion

Symptoms

  • MIL/Warning lamp for communication or coolant system illumination
  • Cooling pump C not operating when commanded; reduced or no coolant flow from that circuit
  • Vehicle may set multiple network-related fault codes
  • Possible localized overheating or reduced cooling performance under certain conditions
  • Intermittent operation of associated cooling/heating functions
  • Related systems (HVAC, engine management) may show degraded function if they rely on that pump data

What to check

  • Read all current and stored codes from all control modules; note freeze frame and occurrence counts
  • Check for other U-codes or CAN bus-related codes (bus-off, invalid data)
  • Visually inspect connectors and wiring at the coolant pump C module for corrosion, damage, or water intrusion
  • Verify power and ground to the pump control module (check fuses, fusible links, module ground points)
  • Check CAN bus wiring continuity and resistance between module connector and network junctions
  • Measure bus termination resistance (expected ~60 ohms across CAN_H and CAN_L with power off)

Signal parameters

  • CAN recessive idle: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (each), differential ≈ 0 V
  • CAN dominant: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V, differential ≈ 2 V
  • Termination resistance approximately 60 ohms across CAN_H and CAN_L (two 120 ohm terminators in parallel)
  • Common CAN data rates: 125 kbps, 250 kbps, 500 kbps (verify vehicle-specific baud rate before capturing)
  • Supply voltage to pump module: typically battery voltage (check vehicle spec)
  • Module ground near 0 ohms to chassis ground when measured with engine off

Diagnostic algorithm

  1. Retrieve codes from all modules and record freeze frame data and occurrence counts. Look for patterns or multiple network faults.
  2. Inspect the physical condition of coolant pump C connector and harness. Unplug connector, check for bent pins, corrosion, water, or debris.
  3. With ignition off, measure resistance between CAN_H and CAN_L at the pump connector; expect ~60 Ω. If open or very high, trace wiring to find open or missing terminator.
  4. Verify supply and ground to the pump module: check fuses, relays, and measure battery voltage at module power pin and near-zero resistance to chassis at ground pin.
  5. Attempt to communicate with the pump module using a scan tool. If module not present, move to wiring and power checks; if present but intermittent, inspect wiring for intermittent faults.
  6. Use a scope or CAN bus analyzer on CAN_H and CAN_L near the pump and at junction points to verify correct recessive/dominant voltages, clean bus signals, and proper message traffic. Look for bus errors, repeated dominant, or a node pulling the bus low/high.
  7. If wiring and bus look good but no module response, bench-test the pump module by applying correct supply and ground per manufacturer procedure or substitute a known-good module when available.
  8. If a failed module is confirmed, replace module and reprogram if required. After repair, clear codes and perform functional test and road test to verify repair.
  9. If intermittent, perform wiggle tests on harness with scope/scan tool connected and use backprobing to reproduce failure; repair damaged wiring and protect connectors.
  10. After repair, verify no other modules set related U-codes and confirm cooling system operation under load.

Likely causes

  • Corroded connector at the coolant pump control module
  • Broken/shorted CAN Low or CAN High wire between pump and main junctions
  • Failed coolant pump electronics due to water ingress or heat damage
  • Blown fuse or lost ground supplying the pump control module
  • Aftermarket device or recent repair disturbed CAN wiring or termination

Fault status

⚠️ Status
The vehicle network lost communication with the Motor Electronics Coolant Pump C control module. This means the module is not responding or its messages are not being received. Possible causes include wiring or connector faults, loss of power/ground, failed pump electronics, or a disrupted CAN bus. Further electrical and network diagnostics are required to confirm the root cause.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.5 - 3.0 hours

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U0640 U0641 U0100 U0073 U0140
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