This code indicates the powertrain control module (PCM) can no longer communicate with the auxiliary electric coolant pump designated "B" over the serial data bus. The loss of signal typically stems from a power interruption, wiring break, or internal failure of the pump’s integrated electronics, preventing the module from commanding or monitoring coolant flow for secondary circuits such as the heater core, turbocharger, or battery cooling.
The electric pump’s internal control module or motor has failed, preventing it from powering on or responding to LIN/CAN bus messages despite receiving voltage.
Opens, shorts-to-ground, or corrosion in the harness between the PCM and Pump B interrupt power, ground, or data lines, often caused by heat exposure or water intrusion at the pump connector.
A blown fuse, faulty relay, or high-resistance ground path removes battery voltage from the pump, causing its communication circuit to go silent.
A short or open in the specific LIN or CAN bus wiring dedicated to this pump isolates it from the network while other modules continue to function.
Rarely, corrupted PCM calibration or incompatible software fails to recognize a functioning pump, potentially requiring a reprogramming update to resolve.
Very rarely, a fault in the PCM’s communication transceiver prevents reception of valid messages from an otherwise operational pump and circuit.
It depends on the pump’s function; if Pump B serves the cabin heater or turbocharger, short drives may be possible, but if it cools the engine or hybrid battery, overheating and severe damage can occur, so immediate diagnosis is advised.
Almost never; this code indicates a communication breakdown with the pump itself or its wiring, and replacing the PCM before verifying the pump, connectors, and harness is usually ineffective.
Pump A typically refers to the primary engine cooling pump, while Pump B is an auxiliary unit for secondary systems such as the heater core, charge air cooler, or battery thermal management, depending on vehicle architecture.
An extremely low voltage event can cause temporary communication errors, but a stored U0624 generally indicates a persistent hardware fault in the pump circuit rather than a history of battery voltage issues.