For 1990-2009 cars

## Fuel Gage Inaccurate or Inoperative Single Tank

### Diagnostic Aids

• | Verify that the fuel level is in the same range as the customer concern.

• | For intermittent diagnosis, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

• | Use the fuel level sender resistance (0-90 ohms) to verify the fuel level sender operation. When the fuel tank is empty the fuel level sender resistance is 0 ohms. When the fuel tank is full the fuel level sender resistance is 90 ohms.

### Test Description

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

1. This step tests for a malfunction in the fuel level sender.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Instrument Cluster Schematics
1 | Did you perform the Instrument Cluster Diagnostic System Check? | -- | Go to Step 2 | Go to Diagnostic System Check - Instrument Cluster
2 |

1. Disconnect the fuel level sender.
2. Connect the J 33431-C Signal Generator and Instrument Panel Tester between the signal circuit of the fuel level sender and the ground circuit of the fuel level sender.
3. Turn the ignition ON, with the engine OFF.

Important: Verify the J 33431-C resistance settings with a DMM.

4. Vary the resistance on the J 33431-C from 0-90 ohms.

Does the fuel gage display empty at 0 ohms and full at 90 ohms?

--

Go to Step 3

Go to Step 4

3 | Inspect for the following items:

• | A poor connection at the harness connector of the fuel level sender. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.

• | A misaligned fuel level sender.

• | A deformed fuel tank.

Did you find and correct the condition?

--

Go to Step 11

Go to Step 6

4 | Test the signal circuit of the fuel level sender for an open, for a short to ground or for a high resistance between the fuel level sender and the IPC. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 5
5 | Test the fuel sender ground circuit for an open or for a high resistance. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 8
6 |

1. Remove the fuel level sender.
2. Inspect for the following items:

• | A stuck fuel level sender, perhaps due to an interference with the fuel strainer.

• | The fuel tank contains foreign material, for instance ice.

Did you find and correct the condition?

--

Go to Step 11

Go to Step 7

7 |

1. With the DMM, measure the resistance of the fuel level sender while moving the float arm.
2. Observe both the analog and digital displays on the DMM.

Does the resistance change smoothly across the specified range?

0-90 ohms

Go to Diagnostic Aids

Go to Step 9

8 | Inspect for poor connections at the harness connector of the IPC. 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 11 | Go to Step 10
9 | Replace the fuel level sender. Refer to Fuel Sender Assembly Replacement in Engine Controls - 8.1L or to the Cat® Medium Duty Diesel Engine Manual - LG5. Did you complete the replacement? | -- | Go to Step 11 | --
10 | Replace the IPC. Refer to Instrument Cluster Replacement . Did you complete the replacement? | -- | Go to Step 11 | --
11 | Operate the system in order to verify the repair. Did you correct the condition? | -- | System OK | Go to Step 2

## Fuel Gage Inaccurate or Inoperative Dual Tank

### Diagnostic Aids

• | Verify that the fuel level is in the same range as the customer concern.

• | For intermittent diagnosis, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

• | Use the fuel level sender resistance (0-90 ohms) to verify the fuel level sender operation. When the fuel tank is empty, the fuel level sender resistance is 0 ohm. When the fuel tank is full the fuel level sender resistance is 90 ohms.

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. This step tests for a malfunction in the fuel level sender.

2. This step tests for a malfunction in the fuel level sensor signal circuit or the IPC.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Instrument Cluster Schematics
1 | Did you perform the Instrument Cluster Diagnostic System Check? | -- | Go to Step 2 | Go to Diagnostic System Check - Instrument Cluster
2 |

1. Disconnect the primary and the secondary fuel level senders.
2. Connect a jumper wire between the signal circuit of the primary fuel level sender and the signal circuit of the secondary fuel level sender.
3. Connect the J 33431-C Signal Generator and Instrument Panel Tester between the signal circuits of the fuel level senders and the ground circuit of the fuel level senders.
4. Turn the ignition ON, with the engine OFF.

Important: Verify the J 33431-C resistance settings with a DMM.

5. Vary the resistance on the J 33431-C from 0-90 ohms.

Does the fuel gage display empty at 0 ohms and full at 90 ohms?

--

Go to Step 4

Go to Step 3

3 |

1. Turn the ignition OFF.
2. Disconnect the fuel tank balance module.
3. Connect the J 33431-C between the fuel level sensor signal circuit and the ground circuit of the fuel tank balance module.
4. Turn the ignition ON, with the engine OFF.

Important: Verify the J 33431-C resistance settings with a DMM.

5. Vary the resistance on the J 33431-C from 0-90 ohms.

Does the fuel gage display empty at 0 ohms and full at 90 ohms?

--

Go to Step 6

Go to Step 5

4 | Inspect for the following items:

• | A poor connection at the harness connectors of the primary and the secondary fuel level senders. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.

• | A misaligned primary or secondary fuel level sender.

• | A deformed primary or secondary fuel tank.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 9

5 | Test the fuel level sensor signal for an open, for a short to ground or for a high resistance between the IPC and the fuel tank balance module. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 8
6 | Test the signal circuits of the primary and the secondary fuel level senders for an open, for a short to ground or for a high resistance between the fuel level senders and the fuel tank balance module. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 7

7 | Test the ground circuit of the primary and the secondary fuel level senders for an open or for a high resistance. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 11
8 | Test the ground circuit of the fuel tank balance module for an open or for a high resistance. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 12
9 |

1. Remove the primary and the secondary fuel level senders.
2. Inspect for the following items:

• | A stuck primary or secondary fuel level sender, perhaps due to an interference with fuel strainer.

• | The primary or the secondary fuel tank contains foreign material, for instance ice.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 10

10 |

1. With the J 39200 DMM, measure the resistance of the primary and the secondary fuel level senders while moving the float arm.
2. Observe both the analog and digital displays on the DMM.

Does the resistance change smoothly across the specified range for both fuel level senders?

0-90 ohms

Go to Diagnostic Aids

Go to Step 13

11 | Inspect for poor connections at the harness connector of the fuel tank balance module. 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 16 | Go to Step 15
12 | Inspect for poor connections at the harness connector of the IPC. 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 16 | Go to Step 14
13 | Replace the fuel level sender that did not have the correct resistance values. Refer to Fuel Sender Assembly Replacement in Engine Controls - 8.1 L or to the Cat® Medium Duty Diesel Engine Manual - LG5. Did you complete the replacement? | -- | Go to Step 16 | --
14 | Replace the IPC. Refer to Instrument Cluster Replacement . Did you complete the replacement? | -- | Go to Step 16 | --
15 | Replace the fuel tank balance module. Refer to Fuel Sender and Balance Pump Control Module Replacement in Engine Controls - 8.1 L or to Cat® Medium Duty Diesel Engine Manual - LG5. Did you complete the replacement? | -- | Go to Step 16 | --
16 | Operate the system in order to verify the repair. Did you correct the condition? | -- | System OK | Go to Step 2