GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2003 🢒 TopKick C-Series (Conventional) C6/C7/C8 🢒 Engine 🢒 Engine Controls - 7.8L 🢒 Fuel Heater Always On

Circuit Description

The fuel manager/filter assembly mounted to the engine consists of the fuel heater and the secondary fuel filter.

The fuel passes through the fuel heater assembly to the secondary fuel filter. The fuel heater assembly contains ceramic heater and a thermostatic switch that opens or closes to turn the heater OFF or ON. The thermostatic switch completes the ground circuit for the fuel heater when fuel temperature is below 8°C (46°F).

The fuel then passes through the fuel filter and to the fuel injection pump.

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check - Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2
  1. Disconnect the fuel heater connector.
  2. Remove the fuel heater from the filter housing.
  3. With the fuel heater at room temperature, connect the ignition 1 voltage circuit of the fuel heater harness connector to battery voltage and connect the ground circuit of the fuel heater harness connector to a good ground.
  4. Observe the heater element.

Does heat occur?

Go to Step 4

Go to Step 3

3
  1. Cool the sensor part of the fuel heater with ice until the heater temperature is below 8°C (46°F).
  2. Connect ignition 1 voltage circuit of the fuel heater harness to battery voltage and connect the ground circuit of the fuel heater harness to a good ground.
  3. Observe the heater element.

Does heat occur?

Go to Step 5

Go to Step 4

4

Replace the fuel heater.

Did you complete the replacement?

Go to Step 5

--

5
  1. Start the engine.
  2. Operate the vehicle within the Condition for which the problem was noted.

Does the fuel heater operate properly?

Go to Step 6

Go to Step 1

6

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

Go to Diagnostic Trouble Code (DTC) List

System OK