Diagnostic Trouble Code (DTC) P1172 or P2636, Fuel Gauge Reads Empty, Service Engine Soon (SES) Light On (Relocate Auxiliary Fuel Tank Vent Hose)

This bulletin is being revised to clarify the difference between the auxiliary fuel tank balance hose and vent hose. Please discard Corporate Bulletin Number 05-06-04-008 (Section 06 -- Engine/Propulsion System).

Some customers may comment that the SES light comes on and the fuel gauge reads empty. when This may occur when the vehicle is parked on an incline with the engine running.

Diagnosis with a scan tool may reveal a DTC P1172 and/or P2636.

Important: A similar condition may occur if the vehicle is fueled with the engine running AND the rear tank is fueled first. The engine must be shut off (as required by law) during vehicle refueling.

The auxiliary fuel tank vent hose is located in the same "T" connection on the main tank vent hose as the auxiliary tank balance hose. During fuel transfer, the fuel is pumped out of the auxiliary tank to the main tank via the balance hose. The fuel is then sucked back into the auxiliary tank via the vent hose rather then dumping the fuel into the main tank. When the Powertrain Control Module (PCM) does not detect a fluid level transfer between the main tank and the auxiliary tank, the PCM shuts off the auxiliary tank pump and the fuel gauge goes to empty.

Follow the service procedure below to correct this condition.

1. Depending on the body upfitter, it may be necessary to raise the vehicle in order to gain access to the auxiliary tank balance hose. Refer to Lifting and Jacking the Vehicle in General Information (SI Document ID #899664).
2. Depending on the body upfitter, it may be necessary to remove the left rear tire/wheel assemblies in order to gain access to the auxiliary tank balance hose. Refer to Tire and Wheel Removal and Installation (SI Document ID #656965).



3. Locate the auxiliary fuel tank vent hose. The vent hose is the smaller diameter of the two hoses that comes from the auxiliary fuel tank and feeds into the main tank vent hose.
4. Disconnect the auxiliary tank vent hose from the main tank vent hose connection. Refer to Quick Connect Fitting(s) Service (Metal Collar) (SI Document ID #802920).
5. Install the cap supplied with kit, P/N 15213990, to the main tank vent hose connector where the auxiliary tank vent hose was just removed.
6. Locate the section of vent hose on the main tank between the fuel filler neck and the metal pipe. The smaller of the two hoses on the filler neck.



7. Cut the main tank vent hose between the filler neck and the metal pipe using an appropriate cutting tool.



8. Install the "T" and the two hose clamps supplied with kit, P/N 15213990, into the main tank vent hose.

Tighten
Tighten the hose clamps to 2.5N·m(22 lb in).

9. Install the new auxiliary tank vent hose and clamp supplied with kit, P/N 15213990, to the "T" that was just installed.

Tighten
Tighten the hose clamp to 2.5N·m(22 lb in).

10. Connect the new vent hose to the original auxiliary tank hose.
11. Secure the newly installed vent hose and the original auxiliary tank vent hose with plastic ties supplied in kit, P/N 15213990.
12. If necessary, reinstall the left rear tires/wheels assemblies. Refer to Tire and Wheel Removal and Installation (SI Document ID #656965).
13. If necessary, lower the vehicle.
14. Using a scan tool, clear the DTCs.
15. Start the vehicle and inspect for leaks.

Important: Advise the customer that a similar condition may occur if the vehicle is fueled with the engine running AND the rear tank is fueled first. The engine must be shut off (as required by law) during vehicle refueling.

Parts are currently available from GMSPO.

For vehicles repaired under warranty, use: