Diagnostic Instructions

DTC Descriptor

DTC P2687 00: Fuel Heater Relay Control Circuit

DTC P2688 00: Fuel Heater Relay Control Circuit Low Voltage

DTC P2689 00: Fuel Heater Relay Control Circuit High Voltage

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
Fuel Heater Relay Coil Ignition	1	1	--	--
Fuel Heater Relay Switch B+	1	1	--	--
Fuel Heater Relay Coil Control	P2688 00	P2687 00	P2689 00	--
Fuel Heater Relay Controlled Output	1	1	1	--
1. The fuse opens and the fuel heater will not operate 2. Fuel Heater Inoperative 3. Fuel Heater Always On

Circuit/System Description

Ignition voltage is supplied to the coil side of the fuel heater relay whenever the ignition is ON. The engine control module (ECM) provides a ground to control the fuel heater relay. When the ECM is commanding the fuel heater ON, the voltage of the control circuit should be low, near 0 volts. When the ECM is commanding the fuel heater OFF, the voltage of the control circuit should be high, near battery voltage.

Conditions for Running the DTC

Conditions for Setting the DTC

P2687 00

The ECM detects the fuel heater relay control circuit is open for greater than 1 s.

P2688 00

The ECM detects the fuel heater relay control circuit is shorted to ground for greater than 1 s.

P2689 00

The ECM detects the fuel heater relay control circuit is shorted to battery for greater than 1 s.

Action Taken When the DTC Sets

DTCs P2687, P2688, and P2689 are type C DTCs.

Conditions for Clearing the DTC

DTCs P2687, P2688, and P2689 are type C DTCs.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Fuel System Description

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Ignition ON, the fuel heater relay with turn ON and the fuel heater will turn ON. The Fuel Temperature Sensor parameter on the scan tool will start to rise.

Circuit/System Testing

1. Ignition OFF, disconnect the KR22 Fuel Heater Relay.
2. Ignition ON, verify that a test lamp does not illuminate between the fuel heater relay coil control circuit terminal 85 and ground.

⇒	If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance.

3. Verify that a test lamp illuminates between the fuel heater relay coil ignition circuit terminal 86 and ground.

⇒	If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, test or replace the KR22 Fuel Heater Relay.

4. Verify that a test lamp illuminates between the fuel heater relay switch B+ circuit terminal 87 and ground.

⇒	If the test lamp does not illuminate, test the fuel heater relay switch B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the F59UA fuse is open, test the control circuit terminal 30 for a short to ground.

5. Disconnect the harness connector X2 at the K20 Engine Control Module (ECM).
6. Test for less than 2 Ω between the ground circuit terminal 30 and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

7. Connect the harness connector at the K20 Engine Control Module (ECM).
8. Connect a 15 A fused jumper wire between the fuel heater relay switch B+ circuit terminal 87 and the control circuit terminal 30. Verify the E11 Fuel Heater is activated.

⇒	If the E11 Fuel Heater does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the E11 Fuel Heater.

9. Connect a DMM, set on the diode setting, between the fuel heater relay control circuit terminal 30 and ground.
10. Ignition OFF, the DMM reading should be greater than 2.5 V or display O.L.

⇒	If less than the specified value, test the control circuit for a short to voltage or short to ground. If the circuits test normal, replace the K20 Engine Control Module (ECM).

11. Ignition ON, the DMM reading should be less than 1 V.

⇒	If greater than the specified value, test the control circuit for an open/high resistance. If the circuits test normal, replace the K20 Engine Control Module (ECM).

12. If all circuits test normal, test or replace the KR22 Fuel Heater Relay.

Component Testing

Relay Test

1. Ignition OFF, disconnect the KR22 Fuel Heater Relay.
2. Test for 70-110 Ω between terminals 85 and 86.

⇒	If the resistance is not within the specified range, replace the KR22 Fuel Heater Relay.

3. Test for infinite resistance between the following terminals:

•

30 and 86

•

30 and 87

•

30 and 85

•

85 and 87

⇒	If not the specified value, replace the KR22 Fuel Heater Relay.

4. Test for less than 2 Ω between terminals 30 and 87A.

⇒	If greater than the specified range, replace the KR22 Fuel Heater Relay.

5. Install a 20 A fused jumper wire between relay terminal  85 and 12 V. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 Ω between terminals 30 and 87.

⇒	If greater than the specified range, replace the KR22 Fuel Heater Relay.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.