GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The fuel level sensor changes resistance in response to the 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 cluster in order to control the fuel gage. The fuel level information is also used for misfire and evaporative emission (EVAP) diagnostics.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0463 Fuel Level Sensor Circuit High Voltage

Conditions for Running the DTC

The ignition is ON.

Conditions for Setting the DTC

    • The fuel level sensor signal is greater than 3 volts.
    • The above condition is present for greater than 10 seconds.

Action Taken When the DTC Sets

    • The fuel gage defaults to empty.
    • The FUEL LEVEL LOW message illuminates in the driver information center (DIC).
    • The PCM records the operating conditions at the time 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

If DTC P0463 and DTC P0651 are set in the PCM, Diagnose DTC P0651 first.

Use the Freeze Frame and/or 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.

Test Description

The number below refers to the step number on the diagnostic table.

  1. Tests for the proper operation of the circuit in the low voltage range.

Step

Action

Value(s)

Yes

No

Schematic Reference: Instrument Cluster Schematics

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

Is DTC P0651 also set in the powertrain control module (PCM)?

--

Go to DTC P0651 in Engine Controls - 4.6L

Go to Step 3

3

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, observe the Fuel Level Sensor parameter in the PCM evaporative emission (EVAP) DATA, data list.

Does the Fuel Level Sensor parameter display greater than the specified value?

3 V

Go to Step 4

Go to Diagnostic Aids

4

  1. Turn OFF the ignition.
  2. Disconnect C420.
  3. Connect a 3-ampere fused jumper between the signal circuit of the fuel level sensor and the low reference circuit of the fuel level sensor, on the female terminal side of the connector.
  4. Turn ON the ignition, with the engine OFF.
  5. With a scan tool, observe the Fuel Level Sensor parameter.

Does the Fuel Level Sensor parameter display less than the specified value?

0.4 V

Go to Step 7

Go to Step 5

5

Test the signal circuit of the fuel level sensor for an open, for a high resistance, or for a short to voltage. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 6

6

Test the low reference circuit of the fuel level sensor for an open, for a high resistance, or for a short to voltage. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 10

7

Test the signal circuit of the fuel level sensor for an open, for a high resistance, or for a short to voltage between C420 and the fuel level sensor. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 8

8

Test the low reference circuit of the fuel level sensor for an open, for a high resistance, or for a short to voltage between C420 and the fuel level sensor. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 9

9

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 13

Go to Step 11

10

Inspect for poor connections at the harness connector of the PCM. 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 13

Go to Step 12

11

Replace the fuel level sensor. Refer to Fuel Level Sensor Replacement in Engine Controls - 4.6L.

Did you complete the replacement?

--

Go to Step 13

--

12

Replace the PCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 13

--

13

  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC.

Does the DTC reset?

--

Go to Step 3

System OK