DTC P2600: Auxiliary Coolant Pump Relay Control Circuit: Description

WARNING: This page is about a different car, the 2002 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

The auxiliary coolant pump is located underhood near the center front of dash. One of its two functions is to maintain constant engine coolant flow to the heater core whenever engine speed is between idle and 1800 RPM with the Engine Coolant Temperature (ECT) between 32-178°F (0-81°C). The second function of the auxiliary coolant pump is to prevent engine coolant boilover after the engine has been turned off with the ECT greater than 229°F (104°C). The pump will run from 4 minutes at 219°F (104°C) or up to 5 minutes at 248°F (120°C) with the engine off (ignition on or off). The ECM controls the auxiliary coolant pump by supplying a ground to the auxiliary coolant pump relay coil control circuit. When the auxiliary coolant pump relay is commanded off, the voltage at the ECM should be high (ignition voltage). When the auxiliary coolant pump relay is commanded on, the voltage at the ECM should be low. The ECM auxiliary coolant pump relay feedback circuit uses a pull-up voltage (2.6-4.6 volts), which allows the ECM to individually differentiate between an open, short to ground or short to voltage. DTC P2600 will set if the ECM detects an open auxiliary coolant pump relay control circuit when auxiliary coolant pump relay is commanded off with engine cranking/running.