Powertrain, generic (extended)

P2636 Fuel Pump B Low Flow/Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

Likely causes

Weak transfer pump not moving enough fuel between tanks
Restricted transfer line or design-related flow limit (GM recall 17067)
Refuelling with engine or ignition on confuses the level-based check
Faulty fuel level sender in one of the tanks

Symptoms

  • Fuel gauge shows empty although the second tank holds fuel
  • Engine may stall when the main tank runs dry
  • Malfunction indicator lamp on

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€100–1,200
Time0.5–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

fuel pump bfuel filterfuel pressure regulator

Related codes

P2635P2632P2633P2634P0461

References: gsi.ext.gm.com, gsi.ext.gm.com, static.nhtsa.gov, static.nhtsa.gov.