Inaccurate Fuel Gauge Readings P1172 P2066 P0461 P2068 And/Or P2636 - keywords dual empty erratic full gage inoperative pump rear sender tank transfer

This PI is being changed to update the parts information. Please discard PIT3630D.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Some customers may comment that their fuel gauge is inaccurate or reads empty on their diesel equipped chassis cab with dual tanks. There may be DTCs P1172, P2066, P0461, P2068, and/or P2636 set in the ECM. This concern may be caused by two different concerns:

1. THIS STEP ONLY APPLIES TO THE LLY OR LBZ 6.6L ENGINES. Root cause may be the float arm is getting hung up on the rear fuel tank filler opening pipe (filler spud) on trucks equipped with the LLY or LBZ diesel engine.
2. Root cause may be the float arm on the rear tank stuck in the up position resulting in setting the sensor card in an open location and driving the gauge to empty. Since the sweep of the rear float arm on diesel trucks is less than the front tank, a plastic rectangular stop was molded into the sensor. However, with certain vertical inputs (loaded vehicle going over bumps), it is possible for the rear tank float arm to jump over the stop and then get stuck on the top of the stop, thus lodging the float arm in the up position and setting the sensor card to an open location.

1. THIS STEP ONLY APPLIES TO THE LLY OR LBZ 6.6L ENGINES. Engineering has shortened the filler spud by approximately 2 1/4 inches. Since the fuel spud is sonic welded into the plastic fuel tank the correction will be to replace the tank assembly with part number 15825666. If the float arm had previously been adjusted it will also have to be replaced with part number 25351753.

Note: To make sure the updated fuel tank is received, measure the length of the fuel spud. With the fuel filler hose removed from the fuel tank measure the length of the filler spud from the longest point inside the fuel tank to the top where the filler hose is installed. The filler spud is cut on an angel inside the tank so make sure the measurement is taken from the tip of the angle. The old design had a filler spud of approximately 11 1/4 inches, and the new design is approximately 9 inches.

2. Engineering has developed a taller stop on the sender card. To correct this concern replace the sender with the following part:

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.