GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The fuel manager/filter assembly consists of the fuel heater, the water-in-fuel sensor, and a filter. The filter contains the coalescer, the device that combines small droplets of water into larger ones, and the filter/separator.

As fuel enters the filter, the fuel passes first though the fuel heater. The heater contains a thermostatic switch that opens or closes to turn the heater OFF or ON, depending on the temperature of the fuel.

The fuel then passes through the filter and the water coalescer, where the droplets of water in the fuel combine into larger drops that fall into the water reservoir in the filter. When fuel flows from the fuel manager/filter assembly to the injection pump, the fuel is clean and free of water.

The fuel heater is operated by a built-in thermostatic switch. The thermostatic switch completes the circuit for the fuel heater element when the thermostatic switch senses a temperature below 8°C (46°F).

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step checks for a fuel heater that is stuck ON.

  2. This steps checks for a thermostatic switch that completes the circuit.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

1

Does the Water In Fuel lamp operating properly?

--

Go to Step 2

Go to Water-in-Fuel Lamp Inoperative or Water-in-Fuel Lamp Always On

2

  1. Disconnect the fuel heater connector and remove the fuel heater from the filter housing. Refer to Fuel Filter Assembly Replacement .
  2. With the fuel heater at room temperature, connect the ignition 1 voltage circuit of the fuel heater to B+ and connect ground circuit of the fuel heater to ground.
  3. Observe the heater element.

Does heat occur?

--

Go to Step 4

Go to Step 3

3

  1. Remove the fuel filter/heater element housing from the vehicle.
  2. Connect the ignition 1 voltage circuit of the fuel heater to battery voltage source and connect the ground circuit of the fuel heater to the ground of the voltage source.
  3. Cool the sensor part of the fuel heater with ice.
  4. Observe the heating element.

Does the thermostatic switch turn ON when the temperature is within the specified range?

-8.4-15.4 °C (16.9-59.8 °F)

Go to Step 5

Go to Step 4

4

Replace the fuel heater. Refer to Fuel Filter Assembly Replacement .

Did you complete the replacement?

--

Go to Step 5

--

5

Operate the vehicle under which the problem was noted.

Does the system operate properly?

--

System OK

Go to Step 1