Circuit Description
The fuel filter/heater element housing consists of the fuel heater, the water-in-fuel sensor, and a filter.
As fuel enters the fuel filter/heater element housing, it first passes though the fuel heater. The heater contains a thermostatic switch that turns the heater ON and OFF, depending on the temperature of the fuel. When the temperature is below 8°C (46°F), the heater is turned ON. When the temperature is above 15°C (59°F), the heater is turned OFF.
The fuel then passes through the fuel filter and the water separator, where the droplets of water combine into larger drops, then fall into the water reservoir located in the bottom of the filter.
When fuel flows from the fuel filter/heater element housing to the fuel injection pump, the fuel is clean and free of water.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematic Icons | ||||
1 | Did you perform the Diagnostic System Check - Engine Controls? | -- | Go to Step 2 | |
2 |
Does the test lamp illuminate? | -- | Go to Step 7 | Go to Step 3 |
3 |
Does the test lamp illuminate? | -- | Go to Step 4 | Go to Step 12 |
4 |
Does the test lamp illuminate? | -- | Go to Step 5 | Go to Step 13 |
5 | Probe the fuel heater relay ground circuit with a test lamp connected to battery voltage. Refer to Troubleshooting with a Test Lamp in Wiring Systems. Does the test lamp illuminate? | -- | Go to Step 6 | Go to Step 14 |
6 |
Does the test lamp illuminate? | -- | Go to Step 16 | Go to Step 10 |
7 |
Does the test lamp illuminate? | -- | Go to Step 8 | Go to Step 11 |
8 |
Does the DMM display the specified value? | ∞ ohms | Go to Step 9 | Go to Step 15 |
9 |
Important: The fuel filter/heater element housing must be cooled to below 8°C (46°F) before the thermostatic switch will turn ON.
Does the thermostatic switch turn ON and heat the element when the temperature is within the specified range? | 8-15°C (46-59°F) | Go to Step 19 | Go to Step 15 |
10 | Repair the open or short to ground in the voltage supply circuit between the fuel filter/heater element housing and the fuel heated relay. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 19 | -- |
11 | 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 19 | -- |
12 | Repair the open or short to ground in the battery voltage circuit of the fuel heater relay. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 19 | -- |
13 | Repair the open or short to ground in the ignition 1 voltage circuit of the fuel heater relay. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 19 | -- |
14 | Repair the open in the ground circuit of the fuel heater relay. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 19 | -- |
15 | Test for an intermittent and for a poor connection at the fuel filter/heater element housing connectors. Refer to Testing for Intermittent Conditions and Poor Connections and Circuit Testing in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 17 |
16 | Test for an intermittent and for a poor connection at the fuel heater relay connection. Refer to Testing for Intermittent Conditions and Poor Connections and Circuit Testing in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 18 |
17 | Replace the fuel filter/heater element housing. Refer to Fuel Filter Assembly Replacement . Did you complete the replacement? | -- | Go to Step 19 | -- |
18 | Replace the fuel heater relay. Did you complete the replacement? | -- | Go to Step 19 | -- |
19 |
Does the fuel heater operate properly? | -- | Go to Step 20 | Go to Step 1 |
20 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |
