Powertrain, generic (extended)

P2635 Fuel Pump A Low Flow/Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

P2635 judges the main fuel pump by its result rather than its wiring: the module compares the measured fuel pressure with the commanded value and flags a pump that falls short or overshoots. GM's 2019 tables do this with filtered rail pressure error against calibrated low and high limits, with pump circuit and pressure sensor codes excluded first, and store it as Type B after two trips; the 2020 diesel table uses the same logic after 40 s of engine running. GM bulletin 16-NA-225 replaces the pump module on 2016-2017 Volt, Malibu, Colorado and Acadia because the pump leaks at the upper manifold. Bentley ties P263500 on the Bentayga W12 to fuel tank noise, and GM bulletin 18-NA-103 to gelled diesel in cold weather. P2636 is the same check for pump B.

Likely causes

Worn or leaking in-tank pump module
Clogged filter or blocked pickup, e.g. gelled diesel in cold weather
Low supply voltage or poor ground at the pump or pump control module
Fuel pressure sensor reading wrong without its own code

Symptoms

  • Hesitation, surging or loss of power under load
  • Hard starting or stalling
  • Whining noise from the fuel tank
  • Malfunction indicator lamp on

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€150–1,200
Time0.5–4 h

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

Parts involved

fuel pumpfuel filterfuel pressure regulator

Related codes

P2636P0087P018BP0230P0627

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