Inaccurate Fuel Gauge Readings (Install New Float Arm, Control Mdl, Harness)

Built before February 16, 1999 and the following VIN breakpoints (T-Series Only):

Some owners/operators may comment about inaccurate fuel gauge readings. The inaccurate readings on T-Series models may result in running out of fuel when the fuel gauge indicates that the fuel tank is 1/4 or 1/2 full. The fuel gauge on C and T-Series models may also indicate full when an additional 40 to 50 gallons (151 to 189 L) of fuel can be added to the tank.

T-Series Gas and Diesel Engines

This condition may be caused by an improperly calibrated fuel gauge for the dual tank system. Also, the float arm geometry may not have sufficient length to accurately account for the amount of fuel in the fuel tank when the tank is full.

C-Series Gas and T-Series Gas and Diesel Engines

Some owners/operators may add fuel to the tanks without turning off the engine. The former fuel transfer pump control module required an ignition key cycle to reset itself in order to transfer fuel from the auxiliary (right) tank to the primary (left) tank.

New fuel level sensor float arms, a fuel transfer control module, and a jumper harness that includes a 330 Ohm resistor have been developed in order to correct this condition. Install the new parts on affected vehicles. Use the following procedure and the part numbers listed below.

Refer to Engine Fuel System, Driveability and Emissions, or the Engine Controls sub-section of the appropriate year Medium Duty Service Manual.

Float Arm Installation -- Both Fuel Tanks; T-Series Only

Use this procedure in order to install a new float arm in both fuel tanks:

1. Disconnect the sender unit electrical connectors from the wire harness assembly.
2. Disconnect the fuel lines from the sender units.
3. Remove the sender units from the fuel tanks.



4. Remove the existing float arms. Place a small, flat screwdriver under the float arm. Pry the float arm (3) out of the two-finger snap retainer (2).
5. Insert the new float arm into the float arm bushing (1).
6. Place the float arm over the two-finger snap retainer.

Important: When Step 7 is complete, tighten the new float arm securely to the sender unit. Be sure that the float arm moves freely. Repeat the procedure for the second tank.

7. Snap the float arm into the retainer.
8. Install the updated sender units in both fuel tanks.
9. Connect the sender unit electrical connectors to the wire harness assembly.
10. Connect the fuel lines to the sender units.

Fuel Gauge Jumper Installation -- T-Series Only

Use this procedure in order to install a new fuel gauge jumper:

1. Disconnect the inline connectors between the rear chassis wiring harness and the fuel tank wiring harness. This connection is found on the crossmember between the fuel tanks near the right frame rail.
2. Attach the jumper harness (1) between the rear chassis harness and the fuel tank harness.
3. Use a band tie (2) in order to secure the jumper back to the regular harness. Loop or double-back the band tie as needed.

Fuel Transfer Control Module Installation -- C- and T-Series

Use the following information to replace the fuel transfer control module:

1. On T-Series models, replace the fuel transfer control module (1). The module is located to the rear of the left fuel tank (2).



2. On C-Series models, replace the fuel transfer control module (2). The module is located at the front of the left fuel tank (1).

Parts are currently available from GMSPO.

For vehicles repaired under warranty, use: