P2635Fuel Pump A Low Flow/Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- 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.
- What you may notice
- Hesitation, surging or loss of power under load
- Hard starting or stalling
- Whining noise from the fuel tank
- Malfunction indicator lamp on
- Likely causes
- LikelyWorn or leaking in-tank pump module
- PossibleClogged filter or blocked pickup, e.g. gelled diesel in cold weather
- PossibleLow supply voltage or poor ground at the pump or pump control module
- RareFuel pressure sensor reading wrong without its own code
- 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: €150 – €1,200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.