U063D

Code

Generic U — Network/User

Lost Communication With Hybrid/EV Electronics Coolant Pump A

Brand: Generic

Type: U — Network/User

Views: UK: 20 EN: 53 RU: 23

AI status

Completed

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Page language: EN

Causes

Open, short or high-resistance wiring in communication bus (CAN or LIN) to the coolant pump controller
Bad connector or corrosion at the pump controller connector
Blown fuse, faulty relay, or loss of power/ground to the pump controller
Faulty coolant pump controller or pump assembly (internal controller failed)
Network bus termination fault or another node pulling the bus low/high
Intermittent connections due to vibration or water ingress

Symptoms

Hybrid/EV coolant pump does not run when commanded or runs intermittently
Hybrid system warning or service message illuminated (HV system, coolant pump fault)
Reduced charging/cooling performance or hybrid system derate
Related fault codes stored in hybrid control module and pump controller (if accessible)
Possible unusual battery or inverter temperatures if pump inactive

What to check

Read all stored DTCs and freeze frame data from hybrid control module and any body/ECM modules; note when fault occurred
Use a network-capable scan tool to request the coolant pump controller and confirm it is present on the bus
Check for other network-related U-codes indicating broader bus issues
Visually inspect wiring, connectors and harness routing to the coolant pump for damage, corrosion, or water intrusion
Check fuses and relays that supply power to the pump controller
Back-probe connector at pump controller: verify supply voltage and ground with ignition on and when pump should run

Signal parameters

CAN bus idle voltages: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (dominant/recessive transitions when active)
CAN bus differential activity: periodic packets/IDs when system is running (packets/sec depends on vehicle)
LIN bus idle: near battery voltage with expected response to master requests
Module supply voltage at pump controller connector: nominal battery/low-voltage system (typically ≈12 V)
Ground voltage at module: close to 0 V (
Pump controller diagnostic response: should acknowledge diagnostic request with module ID

Diagnostic algorithm

Record DTCs and freeze frame data from all modules; note occurrence conditions (ignition state, temperature, driving, charging)
Using a scan tool, attempt to communicate directly with the Coolant Pump A controller; note if the module responds to diagnostic requests
Perform a network scan: verify presence of other modules and look for additional U-codes that indicate bus-wide problems
Visually inspect connectors and harness to the pump for corrosion, pin damage, water ingress, or chafing; repair as needed
Check and verify power and ground at the pump controller connector with a DMM; inspect fuses/relays in the power supply circuit and replace if open
With ignition on, check CAN_H/CAN_L (or LIN) for expected idle voltages and activity using a scope or high-speed DMM; look for missing activity or bus short
Check termination resistance across CAN_H and CAN_L (~60 ohms). If out of range, isolate sections of the bus to locate fault
If module does not respond and wiring/power/ground are good, disconnect the pump controller and bench-test or substitute a known-good module if available
If communications are intermittent, wiggle test wiring and connectors while monitoring bus traffic to reproduce the fault; repair any intermittent wiring or connector issues
After repairs, clear codes and perform functional test cycles (command pump on/off via scan tool, monitor temperatures and communication); road-test and recheck for recurrence
If wiring and hardware are good but fault persists, check for software updates or reprogram the hybrid control module and pump controller per manufacturer procedures

Likely causes

Connector at coolant pump corroded or water-damaged
Power or ground supply to pump controller open or fused
Damaged CAN/LIN wiring between hybrid control module and pump controller
Failed pump controller/module
Fault on the vehicle communication bus (missing termination, short, or another faulty node)

Fault status

⚠️ Status

Lost communication between hybrid control module and Hybrid/EV Electronics Coolant Pump A controller. Pump controller not responding on vehicle network; pump may be disabled or intermittent.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.5-3.0 hours