Circuit Description
The left Fuel Level sensor, mounted in the rear side of the left fuel tank, measures fuel level changes within the left fuel tank. The left Fuel Level Sensor changes resistance based on fuel level. The Fuel Level Sensor has a signal circuit and a ground circuit. The PCM applies a voltage (about 5.0 volts) on the signal circuit to the sensor. The PCM monitors changes in this voltage caused by changes in the resistance of the sensor to determine fuel level.
When the fuel tank is full, the sensor resistance is high, and the PCM's signal voltage is only pulled down a small amount through the sensor to ground. Therefore, the PCM will sense a high signal voltage (fuel tank full). When the fuel tank is empty, the sensor resistance is low, and the signal voltage is pulled down a greater amount. This causes the PCM to sense a low signal voltage (fuel tank empty).
The PCM uses inputs from the Fuel Level Sensor to calculate the total fuel remaining in the fuel tank(s). This information is then sent to the fuel gauge.
When the PCM senses a signal voltage lower than the normal operating range of the sensor, this DTC sets.
The following is a description on how the fuel pump/system functions: An electric high pressure fuel pump attaches to the fuel sender assembly inside the left fuel tank. The fuel pump pumps fuel to the fuel rail assembly at a specified flow and pressure. Excess fuel from the fuel rail assembly returns to the left fuel tank through the return pipe. The fuel pump delivers a constant flow of fuel to the engine even during low fuel conditions and aggressive vehicle maneuvers. The PCM controls the electric fuel pump operation through a fuel pump relay.
The left tank fuel pump also supplies a small amount of pressurized fuel to the right fuel tank siphon jet pump through the fuel feed rear crossover pipe. The pressurized fuel creates a venturi action inside the siphon jet pump. The venturi action causes the fuel to be drawn out of the right fuel tank. Fuel is then transferred from the right fuel tank to the left fuel tank through the fuel sender fuel feed pipe. The fuel system is designed to maintain a greater level in the left fuel tank then the right fuel tank when the electric fuel pump is operating. The fuel transfer rate from the left fuel tank to the right fuel tank is less than the transfer rate from the right fuel tank to the left fuel tank. Therefore, with the electric fuel pump operating, the left fuel tank level should be higher than the right fuel tank level.
The fuel level in the fuel tanks equalize when the following occur:
- The electric fuel pump is not operating.
- The fuel level is greater than 50%.
Conditions for Running the DTC
Engine Running
Conditions for Setting the DTC
| • | Fuel Level Sensor voltage is below 0.39 volts |
| • | Conditions met for 50 seconds |
Action Taken When the DTC Sets
| • | The powertrain control module (PCM) stores the DTC information into memory when the diagnostic runs and fails. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records. |
Conditions for Clearing the DTC
| • | A last test failed, or current DTC, clears when the diagnostic runs and does not fail. |
| • | A history DTC will clear after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic. |
| • | Use a scan tool in order to clear the DTC. |
Diagnostic Aids
Depending on the current fuel level, it may be difficult to locate a malfunctioning sending unit. The malfunction may only occur when the fuel level is full or near empty. The fuel sending unit may need to be removed for further diagnosis. A Fuel Level sensor that has an intermittent condition causes this DTC to set. Remove the Fuel Level sensor refer to Fuel Sender Assembly Replacement in order to check the resistance of the sensor. The resistance of the sensor should change smoothly from 40ohms to 250ohms. Replace the sensor if the resistance did not change smoothly or was out of range.
The voltages in the Fuel Level Conversion Table are approximate values. Use this table to aid in diagnosis.
Fuel Level Conversion Table | ||
|---|---|---|
Approximate Values | ||
Fuel Level | Left Tank voltage | Right Tank Voltage |
100 % | 2.5 V | 2.5 V |
75 % | 2.5 V | 1.5 V |
50 % | 2.5 V | Less than 1.0 V |
25 % | 1.7 V | Less than 1.0 V |
0 % | Less than 1.0 V | Less than 1.0 V |
Important: Remove any debris from the PCM\TAC module connector surfaces before servicing the PCM\TAC module. Inspect the PCM\TAC module connector gaskets when diagnosing/replacing the modules. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion into the PCM\TAC modules.
The following occurs with this DTC set:
| • | The vehicle fuel gauge displays empty. |
| • | The Check Gauge lamp illuminates. |
| • | The Driver Information Center displays a message. |
Using Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data can aid in determining how many miles since the DTC set. The Fail Counter and Pass Counter can also aid determining how many ignition cycles the diagnostic reported a pass and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that you observed. This will isolate when the DTC failed.
Test Description
The numbers below refer to the step numbers on the Diagnostic Table.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
2 |
Did DTC P1639 Fail This Ignition cycle? | -- | ||
Is the Fuel Level sensor above the specified value? | 0.39 V | |||
4 |
Does the scan tool indicate that this diagnostic failed this ignition? | -- | Refer to Diagnostic Aids | |
5 |
Is the Fuel Level sensor above the specified value? | 0.39 V | ||
6 |
Was the Fuel Level sensor signal circuit grounded? | -- | ||
7 | Replace the Fuel Level sensor. Refer to Fuel Sender Assembly Replacement . Is the action complete? | -- | -- | |
8 |
Did you find and correct the condition? | -- | ||
9 |
Important: Program the replacement PCM. Refer to Powertrain Control Module/Throttle Actuator Control Module Replacement . Replace the PCM. Is the action complete? | -- | -- | |
10 |
Does the scan tool indicate that this test ran and passed? | -- | ||
11 | Select the Capture Info option and the Review Info option using the scan tool. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK |
