Circuit Description
The fuel level sensor changes resistance in response to fuel level. The engine control module (ECM) monitors the signal circuit of the fuel level sensor in order to determine the fuel level. When the fuel tank is full, the sensor resistance is high and the ECM senses a high signal voltage. When the fuel tank is empty, the sensor resistance is low and the ECM senses a low signal voltage. The ECM uses the signal circuit of the fuel level sensor in order to calculate the percentage of remaining fuel in the tank. The ECM sends the fuel level percentage via the class 2 serial data circuit to the instrument cluster in order to control the fuel gage.
This diagnostic tests for a lower than normal fuel level sender signal for a single tank or for a lower than normal primary fuel level sender signal for dual tanks.
Conditions for Running the DTC
The engine is running.
Conditions for Setting the DTC
| • | The primary fuel level signal on vehicles with dual tanks or the fuel level signal on vehicles with single tank is less than 3.5 percent. |
| • | The above condition is present for greater than 20 seconds. |
Action Taken When the DTC Sets
| • | The fuel gage defaults to empty. |
| • | The ECM records the operating conditions at the time that the diagnostic test fails. The ECM displays the failure information in the Failure Records on the scan tool. |
Conditions for Clearing the DTC
| • | The DTC becomes history when the conditions for setting the DTC are no longer present. |
| • | The history DTC clears after 40 malfunction free warm-up cycles. |
| • | The ECM receives the clear code command from the scan tool. |
Diagnostic Aids
| • | Use the Freeze Frame/Failure Records data in order to locate an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records data may help in determining the number of miles since the DTC set. The Fail Counter and Pass Counter can also help in determining the number of ignition cycles that the diagnostic test reported a pass and/or fail. Operate the vehicle within the same freeze frame conditions, including those for RPM, for engine load, for vehicle speed, for temperature, and for others. This will isolate at what point the DTC failed. |
| Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. |
| • | When the fuel level sensor signal is lower than normal, the Fuel Level Sensor % parameter in the ECM Fuel System data list on the scan tool indicates a value less than 4 percent for a single tank. |
| When the primary fuel level sensor signal is lower than normal, the Fuel Level Sensor % parameter in the ECM Fuel System data list on the scan tool indicates a value about half the actual fuel level for dual tanks. |
Test Description
The number below refers to the step number on the diagnostic table.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Instrument Cluster Schematics | ||||
1 | Did you perform the Instrument Cluster Diagnostic System Check? | -- | Go to Step 2 | |
2 |
Does the scan tool indicate that the Fuel Level Sensor % parameter is less than the specified value? | 4% (single tank) or 50% (dual tanks) | Go to Step 3 | Go to Diagnostic Aids |
Does the scan tool indicate that the Fuel Level Sensor % parameter is greater than the specified value? | 98% (dual and single tanks) | Go to Step 5 | Go to Step 4 | |
4 | Test the signal circuit of the fuel level sensor for a short to ground. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 6 |
5 | Inspect for poor connections at the harness connector of the fuel level sensor. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 7 |
6 | Inspect for poor connections at the harness connector of the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 8 |
7 | Replace the fuel level sensor. Refer to Fuel Sender Assembly Replacement in Engine Controls - 7.8L. Did you complete the replacement? | -- | Go to Step 9 | -- |
8 |
Important: Program the replacement ECM. Replace the ECM. Refer to Engine Control Module Replacement/Restore Fuel Rate Data in Engine Controls - 7.8L. Did you complete the replacement? | -- | Go to Step 9 | -- |
9 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
