| Table 1: | Fuel Level Sensor Inspection |
Circuit Description
The powertrain control module (PCM) uses the fuel level input from the fuel level sensor in order to calculate the expected vapor pressures within the fuel system. Vapor pressures vary as the fuel level changes. Vapor pressure is critical to determining if the EVAP control system is operating properly. Fuel level information is used in determining whether to run an EVAP control system diagnostic. A fuel level that is too high or too low may prevent the EVAP control system diagnostics from accurately detecting a fault.
Conditions for Setting the DTC
The change in fuel level from maximum to minimum is less than 1 gallon even though the volume of intake air is calculated to be more than 660 kg.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) after two consecutive ignition cycles in which the diagnostic runs with the fault active. |
| • | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after three consecutively passing trips without a fault present. |
| • | A History DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | DTCs can be cleared by using a scan tool or by disconnecting the PCM battery feed. |
Diagnostic Aids
Check for any of the following conditions:
| • | If a DTC P0463 is also displayed, diagnose that DTC first. |
| • | A stuck fuel level sensor may cause a DTC P0461 to set. |
| • | A loose fuel tank baffle that may interfere with the movement of the fuel level sensor float. |
| • | A corroded or loose fuel level sensor chassis ground. Operate the tail lamps and brake lamps while checking the fuel level sensor reading on a scan tool. Increasing the current flow through the G400 chassis ground can reveal a faulty circuit connection. |
| • | A faulty electrical connection at the PCM. |
Check the resistance of the fuel level sensor at the following positions:
Fuel Level Position | Resistance Measurement |
|---|---|
Full Tank | 10 ohms or less |
Half Tank | 30 to 35 ohms |
Empty Tank | 120 ohms or more |
An open in the fuel level sensor circuit will indicate a 0% fuel level (empty fuel tank), while a short to ground in the fuel level sensor circuit will indicate a 100% fuel level (full fuel tank).
An intermittent malfunction may be caused by a fault in the fuel level sensor electrical circuit. Inspect the wiring harness and components for any of the following conditions:
| • | Backed out terminals |
| • | Improper mating of terminals |
| • | Broken electrical connector locks |
| • | Improperly formed or damaged terminals |
| • | Faulty terminal to wire connections |
| • | Physical damage to the wiring harness |
| • | A broken wire inside the insulation |
| • | Corrosion of electrical connections, splices, or terminals |
If the DTC P0461 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.
Test Description
The numbers below refer to the step numbers in the Diagnostic Table.
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The Powertrain OBD System Check prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
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This step checks the circuit from the fuel level sensor to the PCM. Because the scan tool will display a default value of 100% all the time when a fuel level sensor circuit DTC is present, any current or stored fuel level sensor circuit DTCs (DTC P0461 or P0463) must be cleared before reading the fuel level parameter on the scan tool.
-
This step checks for a faulty fuel level sensor.
Step
| Action | Value(s) | Yes | No |
|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||
2 |
Is the voltage near the specified value? | 7-8 volts | ||
3 |
Is the voltage near the specified value? | 7-8 volts | ||
4 |
Was a repair necessary? | -- | ||
|
Important: In order to avoid an incorrect fuel level reading on the scan tool, any current or stored fuel level DTCs should be cleared.
Does the fuel tank level display on the scan tool increase to the first specified value and then decrease steadily to the second specified value when the float is swept from one end to the other? | 90% 0% | Fault not Present-Go to Diagnostic Aids | ||
|
Important: The fuel gauge responds slowly to changes in the position of the fuel sensor float. Continue to slowly move the fuel tank sensor float from the empty position and then back to the full position while observing the fuel gauge on the I/P. Does the I/P fuel gauge indicate a full and an empty fuel tank when the float is swept from one end to the other? | -- | |||
7 |
Was a repair necessary? | -- | ||
8 | Repair the open or the short in the fuel level sensor signal (input) wire between the fuel level sensor harness connector located under the rear seat cushion and the fuel level sensor. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
9 | Replace the fuel level sensor. Refer to Fuel Level Sensor Replacement . Is the action complete? | -- | -- | |
10 |
Does the DMM read within the specified value? | 7 to 8 volts | ||
11 |
Was a repair necessary? | -- | ||
12 |
Was a repair necessary? | -- | ||
13 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | -- | |
14 |
Are any DTCs displayed on the scan tool? | -- | Go to the Applicable DTC Table | System OK |
