Functional Description - Auxiliary Coolant Pumps
The auxiliary coolant pumps are a smart device used to circulate coolant through the cooling system. The pumps are provided either a direct fused battery feed or fused ignition feed (refer to the wiring information) and a chassis ground. The smart pumps are controlled using a LIN bus communication line. The controlling Electronic Control Unit (ECU) will send a command with an rpm request to the pump electronics. The auxiliary coolant pump will operate the pump motor and monitor the internal motor operation and circuitry for faults. The auxiliary coolant pump communicates feedback to the ECU regarding the following operating parameters and failure modes:
- Motor rpm target
- Motor rpm actual
- Motor temperature
- Motor current
- Dry run operation error
- Blocked pump error
- Overtemp condition error
- Over current condition error
- Voltage error
- Fail Safe activated
DIAGNOSTICS:
The ECU will set a performance fault against the faulty auxiliary coolant pump when a failure is reported by the pump. The failure can be due to an internal circuit issue, or some type of system failure such as low coolant or restricted flow. Air pockets will cause a dry run condition. The pump can detect this either by detecting a low current draw or higher than expected pump speed. Or in some cases, both conditions being present. A blocked pump or excessive restriction in the coolant flow can cause a high current draw or lower than expected pump speed. These possible mechanical failures should be investigated before condemning an auxiliary coolant pump with a performance fault set against it.
When communication between the ECU and the auxiliary coolant pump is lost, the ECU will set a corresponding loss of communication DTC against the pump. Communication can be lost due to an open or shorted LIN bus line, or if the auxiliary coolant pump loses battery feed or chassis ground.