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 the fuel enters the filter, the fuel passes through 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 15.4°C (59.8°F).

Test Description

The number below refers to the step number on the diagnostic table.

  1. 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 harness connector from the top of the fuel filter/heater element housing.
  2. Turn ON the ignition with the engine OFF.
  3. Probe the fuel heater ignition 1 voltage circuit with a test lamp connected to a good ground. Refer to Troubleshooting with a Test Lamp in Wiring Systems.

Does the test lamp illuminate?

--

Go to Step 3

Go to Step 5

3

Probe the fuel heater ground circuit at the fuel filter/heater element housing with a test lamp connected to B+. Refer to Troubleshooting with a Test Lamp in Wiring Systems.

Does the test lamp illuminate?

--

Go to Step 4

Go to Step 10

4

  1. Remove the fuel filter from the fuel filter/heater element housing.
  2. Test the ignition 1 voltage circuit and the ground circuit for an open in the fuel filter/heater element housing. Refer to Troubleshooting with a Digital Multimeter in Wiring Systems.

Did either circuit test open?

--

Go to Step 11

Go to Step 7

5

Is the fuel HT fuse open?

--

Go to Step 6

Go to Step 8

6

  1. Disconnect the intake air heater harness connector.
  2. Probe the ignition 1 voltage circuit with a test lamp connected to B+. Refer to Troubleshooting with a Test Lamp in Wiring Systems.

Does the test lamp illuminate?

--

Go to Step 9

Go to Step 7

7

  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 13

Go to Step 12

8

Repair the open in the ignition 1 voltage circuit between the fuel filter/heater element housing and the Fuse. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 14

--

9

Repair the short to ground on the ignition 1 voltage circuit . Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 14

--

10

Repair the open in the ground circuit between the fuel filter/heater element housing and chassis ground. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 14

--

11

Replace the fuel filter/heater element housing. Refer to Fuel Filter Assembly Replacement .

Did you complete the replacement?

--

Go to Step 14

--

12

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

Did you complete the replacement?

--

Go to Step 14

--

13

Replace the intake air heater relay. Refer to Intake Air Heater Relay Replacement .

Did you complete the replacement?

--

Go to Step 14

--

14

Operate the vehicle under which the problem was noted.

Does the system operate properly?

--

System OK

Go to Step 1