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U0648 — Lost Communication Motor Electronics Coolant Pump C

Generic OBD-II · all makesNetwork / communication

U0648 indicates that the vehicle's control network has lost communication with the motor‑electronics coolant pump designated as "C". The pump's control module is no longer transmitting or receiving data on the CAN bus, so the PCM cannot monitor or command its operation.

Symptoms

What causes it — most likely first

1. Open or shorted communication wiring to pump C

Damaged, corroded, or disconnected CAN‑high/CAN‑low wires or connector pins prevent data exchange.

2. Faulty coolant pump C control module

Internal failure of the pump's electronic controller stops it from participating on the bus.

3. CAN bus termination or bus‑wide fault

Missing or damaged termination resistors, a short on the bus, or another node pulling the bus down can isolate pump C.

4. Poor ground or power supply to pump C module

Insufficient voltage or a high‑resistance ground causes the module to reset or stay offline.

5. PCM/ECM internal communication fault

Rare; a hardware defect in the PCM's CAN controller can prevent it from seeing pump C, but this is seldom the root cause.

How it's diagnosed

  1. Retrieve all stored codes and note any other CAN‑communication faults.
  2. Visually inspect the wiring harness and connectors leading to coolant pump C for damage, corrosion, or loose pins.
  3. Measure continuity and resistance of the CAN‑high and CAN‑low circuits between the PCM and pump C connector.
  4. Verify that the pump C module receives proper voltage and ground per the service specifications.
  5. Check CAN bus termination resistance (typically 60 Ω total) and look for bus‑short conditions with a scope or bus analyzer.
  6. If wiring, power, ground, and bus integrity are confirmed, test or replace the pump C control module.

Code facts & related codes

SystemNetwork / communication
StandardizationSAE generic — identical on every make
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Frequently asked

Does U0648 mean the PCM is defective?

In the vast majority of cases the PCM is not the cause; the fault is usually wiring, a connector, or the pump's own control module.

Can the vehicle be driven safely with this code present?

Driving is not recommended because loss of pump C communication can lead to inadequate coolant flow and overheating.

Will clearing the code permanently fix the problem?

Clearing only removes the stored code; if the underlying communication fault remains, the code will return.

Is a software update ever required for U0648?

A software update is only needed if a manufacturer‑issued technical service bulletin specifically addresses a CAN‑communication issue for this pump.