Circuit Description
The fuel level sensor changes resistance in response to fuel level. The powertrain control module (PCM) 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 PCM senses a high signal voltage. When the fuel tank is empty, the sensor resistance is low and the PCM senses a low signal voltage. The PCM uses the signal circuit of the fuel level sensor in order to calculate the percentage of remaining fuel in the tank. The PCM sends the fuel level percentage via the class 2 serial data circuit to the instrument panel cluster (IPC) in order to control the fuel gage. The fuel level information is also used for misfire and evaporative emission (EVAP) diagnostics for gas engines only.
This diagnostic tests for a lower than normal fuel level sensor 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 ignition is ON. |
| • | The engine is running (LG4). |
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 0.5 volts (LB7, LLY and L18). |
| • | 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 (LG4). |
| • | The above condition is present for greater than 20 seconds. |
Action Taken When the DTC Sets
| • | The fuel gage defaults to empty. |
| • | The PCM records the operating conditions at the time that the diagnostic test fails. The PCM 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 PCM 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, engine load, vehicle speed, temperature, and 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% for a single tank (LG4 only). 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 (LG4 only). |
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 Connector End View Reference: Master Electrical Component List in Wiring Systems | ||||||||||||
1 | Did you perform the Diagnostic System Check - Instrument Cluster? | -- | Go to Step 2 | |||||||||
2 |
Does the scan tool indicate that the fuel level sensor parameter is less than the specified value? | 0.5 V (LB7, LLY and L18) 50% (LG4 only) | 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? | 4.5 V (LB7, LLY and L18 only) 98% (LG4 only) | 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 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 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 powertrain control module (PCM) or the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and 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:
Did you complete the replacement? | -- | Go to Step 9 | -- | ||||||||
8 |
Important: Program the replacement PCM or ECM. Replace the PCM or ECM. Refer to:
Did you complete the replacement? | -- | Go to Step 9 | -- | ||||||||
9 |
Does the DTC reset? | -- | Go to Step 2 | System OK | ||||||||
