After Boil Coolant Pump Always On

/ 9-4x / 2011 / 2. Engine / Cooling system / Fault diagnosis, fault symptoms / After Boil Coolant Pump Always On

Diagnostic Instructions

•	Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

•	Review Strategy Based Diagnosis for an overview of the diagnostic procedure.

•	Diagnostic Procedure Instructions provides an overview of the diagnostic category.

Circuit/System Description

The auxiliary coolant pump and cooling fan system provides a measure of prevention against fuel vaporization due to excessive engine temperatures. The engine control module (ECM) commands the auxiliary or after boil coolant pump ON when the engine coolant temperature exceeds a calibrated value after engine shut down. The ECM applies ground to the coil side of the auxiliary pump circuit board (PCB) relay. This energizes the coil and applies voltage directly to the pump motor through the switch side of the relay.

Diagnostic Aids

The auxiliary coolant pump relay is a circuit board (PCB) relay. The relay is an integral component to the underhood bussed electrical center (UBEC). It cannot be removed and it is not visible.

Reference Information

Schematic Reference

Engine Cooling Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Cooling Fan Description and Operation (LF1) Cooling Fan Description and Operation (LAU)

Electrical Information Reference

•	Circuit Testing

•	Connector Repairs

•	Testing for Intermittent Conditions and Poor Connections

•	Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1.	Ignition ON, observe the DTC information with a scan tool. Verify that DTC P2600, P2602, or P2603 is not set.

2.	If any auxiliary coolant pump DTC is set, repair the DTC first. Refer to DTC P2600-P2603 .

3.	Ignition ON, observe the scan tool engine coolant temperature (ECT) sensor parameter. Verify the ECT is colder than 110 °C (230 °F).

4.	Observe that the pump is not activated.

Circuit/System Testing

1.	Ignition OFF, remove the AFTERBOIL PUMP Fuse 4.

2.	Ignition ON, observe that the auxiliary coolant pump is not activated.

3.	If the pump is activated, test for a short to voltage in the KR31 auxiliary coolant pump relay controlled output circuit.

4.	If the pump is not activated, test or replace the X50A underhood fuse block (UBEC).

Component Testing

1.	Ignition OFF, disconnect and remove the X50A UBEC.

2.	Remove the KR75 powertrain relay.

3.	Test for 170-210 Ω between the powertrain relay switched output circuit terminal 87 and the auxiliary coolant pump relay control circuit at UBEC terminal X2-21.

4.	If not within the specified range, replace the X50A UBEC.

5.	Test for greater than 2 Ω between UBEC B+ supply cable and the AFTERBOIL PUMP Fuse 4.

6.	If less than the specified range, replace the X50A UBEC.

7.

Connect a 10 A fused jumper wire from the positive terminal of the battery to the powertrain relay switched output circuit terminal 87. Connect a jumper wire from the negative terminal of the battery to the auxiliary coolant pump relay control circuit at UBEC terminal X2-21. Test for less than 2 Ω between UBEC B+ supply cable and the AFTERBOIL PUMP Fuse 4.

8.	If greater than the specified range, replace the X50A UBEC.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Front Compartment Fuse Block Replacement

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