GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The primary fuel level sensor and the secondary fuel level sensor changes resistance in response to the fuel level. The powertrain control module (PCM) monitors the signal circuit of the primary fuel level sensor and the secondary fuel level sensor in order to determine the fuel level. When the fuel tanks are full, the resistance of both fuel level sensors are high and the PCM senses a high signal voltage on both the signal circuits of the primary fuel level sensor and the secondary fuel level sensor. When the fuel tanks are empty, the resistance of the fuel level sensors are low and the PCM senses a low signal voltage. The PCM uses the signal circuits of the primary fuel level sensor and the secondary 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.

This diagnostic tests for a higher than normal secondary fuel level sensor signal.

Conditions for Running the DTC

The ignition is ON.

Conditions for Setting the DTC

    • The secondary fuel level signal is greater than 4.5 volts.
    • 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 numbers below refer to the step numbers 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 References: Instrument Panel, Gages, and Console Connector End Views , Powertrain Control Module Connector End Views in Engine Controls - 4.3L or Powertrain Control Module Connector End Views in Engine Controls - 4.8L, 5.3L, and 6.0L

1

Did you perform the Instrument Cluster Diagnostic System Check?

--

Go to Step 2

Go to Diagnostic System Check - Instrument Cluster

2

  1. Install a scan tool.
  2. Turn the ignition ON, with the engine OFF.
  3. With a scan tool, observe the Fuel Level Sensor Rear parameter in the PCM Enhanced EVAP data list.

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

4.5 V

Go to Step 3

Go to Diagnostic Aids

3

  1. Turn the ignition OFF.
  2. Disconnect C101.
  3. Connect a 3-ampere fused jumper wire between the signal circuit of the secondary fuel level sensor and the low reference circuit of the secondary fuel level sensor on the female terminal side of the connector.
  4. Turn the ignition ON, with the engine OFF.
  5. With a scan tool, observe the Fuel Level Sensor Rear parameter in the PCM Enhanced EVAP data list.

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

0.5 V

Go to Step 6

Go to Step 4

4

Test the signal circuit of the secondary 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 secondary 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 secondary fuel level sensor for an open, for a high resistance, or for a short to voltage between C101 and the secondary 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 secondary fuel level sensor for an open, for a high resistance, or for a short to voltage between C101 and the secondary 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 secondary 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 powertrain control module (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 secondary fuel level sensor. Refer to:

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

Did you complete the replacement?

--

Go to Step 12

--

11

Important: Program the replacement PCM.

Replace the PCM. Refer to:

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

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.

Does the DTC reset?

--

Go to Step 2

System OK