U0649

Code

Generic U — Network/User

Lost Communication With Coolant Pump D

Brand: Generic

Type: U — Network/User

Views: UK: 23 EN: 34 RU: 23

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Page language: EN

Causes

Open or shorted wiring between ECM/BCM and coolant pump module
Blown fuse or missing power/ground to the coolant pump module
Corroded, pinched or disconnected connector at the pump module or gateway
Faulty coolant pump control module or pump assembly
CAN/LIN bus fault (missing termination, short to voltage/ground, noise)
Software mismatch or failed module programming after replacement

Symptoms

MIL (check engine) or network warning lamp and stored U0649 code
Coolant pump D may not run or operates unpredictably
Reduced cooling performance, elevated coolant temperature or fan cycling
Instrument cluster message indicating pump or cooling system fault
Multiple network communication DTCs present (indicating bus-wide issue)

What to check

Connect a scan tool; read all U-codes and freeze-frame data and note time-stamps
Check for other network codes (U0100, U0121, U1000 etc.) that suggest bus problems
Visually inspect connectors and wiring at the coolant pump module and nearby harnesses for corrosion, damage, or water ingress
Verify fuses and relays related to coolant pump power and control
Measure battery voltage (key on) and verify stable supply to the module
Perform a wiggle test on wiring while monitoring communications to reproduce intermittent faults

Signal parameters

CAN bus idle voltages: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (recessive). Dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V
Typical CAN data rates: 250 kbps or 500 kbps depending on vehicle — verify manufacturer spec
Expected: regular messages from coolant pump module at a steady interval (module-specific ID & period)
Termination resistance across CAN_H and CAN_L ≈ 60 Ω (two 120 Ω in parallel)
LIN (if used): idle ≈ battery voltage, wake/pulse patterns per manufacturer; single-wire checks with scope recommended

Diagnostic algorithm

Use a capable scan tool to confirm U0649 and any related codes. Record freeze frame and reattempt communication with the coolant pump module.
Check for other U-codes indicating a global bus failure. If many modules are offline, suspect a network power/termination issue or gateway failure before module-level repair.
Visually inspect connectors, harness, and pump module for damage, corrosion, moisture. Repair or clean connectors as needed following manufacturer practices.
Verify power and ground at the coolant pump module with key ON (use DVOM). Compare to vehicle specs; check associated fuses and relays.
With ignition ON, measure CAN_H and CAN_L voltages at the pump module connector and at a known-good node. Look for expected idle voltages and absence of short to battery/ground.
Check termination resistance across CAN_H/CAN_L with power off — should be about 60 Ω. If abnormal, trace for missing/shorted terminator.
If network voltages and wiring are good but no communication, attempt to communicate from scan tool while backprobing the module connector to confirm if the module transmits any messages.
If intermittent, perform a wiggle test while monitoring bus data to localize broken wires or pinched sections. Inspect routes near hinges, engine mounts, and other high-movement areas.
If wiring and bus are functional, consider module failure or software issue. Check for available technical service bulletins (TSBs) and verify correct module part number and programming level.
After repair or replacement, clear codes, reprogram if required, and road-test to confirm communication remains stable. Re-scan to ensure no recurrence.