P2636Fuel Pump B Low Flow/Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- P2636 is the flow check for fuel pump B, in practice mostly the transfer pump of trucks with two tanks. GM's 2014 table for the 6.6 L LML compares how fast the levels in both tanks fall while the pump runs; if they do not move as expected for 140 s, a Type B fault is stored. The 2020 diesel table weighs a commanded transfer of 5 litres against the level change in the main tank (limit 2.5 litres, 1,000 s), or flags a rear tank still holding over 141 litres after 1,150 s of pumping; both give Type C. Emission recall 17067 for 2015-2016 Silverado/Sierra HD LML with tanks N2N notes that the MIL comes on, the fuel gauge drops to empty and transfer is blocked; dealers re-plumb the lines and reflash the ECM. PIT5208A attributes a false P2636 to refuelling with the engine or ignition on.
- What you may notice
- Fuel gauge shows empty although the second tank holds fuel
- Engine may stall when the main tank runs dry
- Malfunction indicator lamp on
- Likely causes
- LikelyWeak transfer pump not moving enough fuel between tanks
- PossibleRestricted transfer line or design-related flow limit (GM recall 17067)
- PossibleRefuelling with engine or ignition on confuses the level-based check
- RareFaulty fuel level sender in one of the tanks
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €100 – €1,200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.