GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The fuel level sensor changes resistance in response to fuel level. The 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 EVAP diagnostics.

Conditions for Running the DTC

The ignition is ON.

Conditions for Setting the DTC

    • The fuel level signal is greater than 98 percent.
    • The above condition is present for greater than 20 seconds.

Action Taken When the DTC Sets

    • The fuel gage defaults to empty.
    • The low fuel indicator illuminates.
    • 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, 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

Connector End View Reference: Master Electrical Component List

1

Did you perform the Instrument Cluster Diagnostic System Check?

--

Go to Step 2

Go to Diagnostic System Check - Instrument Cluster

2

  1. Install the scan tool.
  2. Turn the ignition ON, with the engine OFF.
  3. With the scan tool, observe one of the following fuel level parameters:
  4. • Fuel Tank Level Remaining parameter in the PCM Enhanced EVAP Data data list-gas only.
    • Fuel Level Sensor parameter in the PCM Fuel System data list-6.6L diesel only.

Does the scan tool indicate that the Fuel Tank Level Remaining or the Fuel Level Sensor parameter is greater than the specified value?

98%

4.5 V-6.6L diesel only

Go to Step 3

Go to Diagnostic Aids

3

  1. Turn the ignition OFF.
  2. Disconnect C152.
  3. Connect a 3 amp fused jumper wire between the signal circuit of the fuel level sender and the low reference circuit of the fuel level sender on the male terminal side.
  4. Turn the ignition ON, with the engine OFF.
  5. With the scan tool, clear the DTCs.
  6. With the scan tool, observe the fuel level parameter.

Does the scan tool indicate that the Fuel Tank Level Remaining or the Fuel Level Sensor parameter is less than the specified value?

4%

0.5 V-6.6L diesel only

Go to Step 6

Go to Step 4

4

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 12

Go to Step 5

5

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 12

Go to Step 9

6

Test the signal circuit of the fuel level sensor for an open, for a high resistance, or for a short to voltage between C152 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 12

Go to Step 7

7

Test the low reference circuit of the fuel level sensor for an open, for a high resistance, or for a short to voltage between C152 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 12

Go to Step 8

8

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 12

Go to Step 10

9

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 12

Go to Step 11

10

Replace the fuel level sensor. Refer to the following procedures:

    •  Fuel Level Sensor Replacement in Engine Controls - 4.3L
    •  Fuel Level Sensor Replacement in Engine Controls - 4.8L, 5.3L and 6.0L
    •  Fuel Level Sensor Replacement in Engine Controls - 6.6L
    •  Fuel Level Sensor Replacement in Engine Controls - 8.1L

Did you complete the replacement?

--

Go to Step 12

--

11

Important: Program the replacement PCM.

Replace the PCM. Refer to the following procedures:

    •  Powertrain Control Module Replacement in Engine Controls - 4.3L
    •  Powertrain Control Module Replacement in Engine Controls - 4.8L, 5.3L and 6.0L
    •  Engine Control Module Replacement in Engine Controls - 6.6L
    •  Powertrain Control Module Replacement in Engine Controls - 8.1L

Did you complete the replacement?

--

Go to Step 12

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12

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

Does the DTC reset?

--

Go to Step 2

System OK