P2635: The engine computer has found that fuel pump A isn't delivering the flow or pressure it is being commanded to deliver
Fuel pump A low flow/performance
Severity: Inspect soon
KBB says the car may be drivable but recommends against it, because a starved engine runs lean and can misfire. GM bulletins describe hesitation, surging and stalling, so get it diagnosed soon.
It gets more serious if:
- Stop: Stop somewhere safe and have the car towed if the engine stalls, surges or loses power while you are driving, or starts and then dies. A fuel supply that cuts out can leave you without power in traffic.
P2635 in short
P2635 means the fuel pump isn't delivering the flow or pressure the engine computer is asking for. A weak or failing in-tank pump is the usual cause, and GM has replaced pump modules for hot-weather vapor problems. A faulty fuel pressure sensor can also set it. Get it checked soon; stop if the engine stalls.
Many newer engines run the in-tank fuel pump at variable speed and watch a fuel pressure sensor to check the result. P2635 sets when the pressure or flow falls short of what was commanded.
A worn pump is the obvious cause, but GM bulletins show other patterns: fuel vapor building up in the feed line in temperatures above 100 F, a pump that whines and cuts out below about 20 F, and a pressure sensor that misreads low pressure.
Because the engine can run lean when fuel falls short, misfire and poor economy can follow.
Most likely causes
Cause 1: Weak or failing fuel pump module
Supported by vehicle data- Why it ranks here
- KBB lists a failing pump first, and several GM bulletins replace the fuel pump module for P2635.
- What would change this
- Likelier with hesitation under load, a whining pump, or trouble in very hot or very cold weather.
Cause 2: Fuel pressure sensor misreading
Supported by vehicle data- Why it ranks here
- GM's PIP5286B traces P2635 with P018B to a pressure sensor that still reads 30-40 psi after depressurising.
- What would change this
- Likelier if P018B is stored too and the pressure reading never drops to zero.
Cause 3: Clogged injectors or another fuel restriction
Possible — needs testing- Why it ranks here
- KBB lists clogged injectors and other fuel-system faults.
- What would change this
- Likelier if fuel pressure is fine but cylinders still run lean.
What to test first
Start at step 1. Each result tells you what it means and where to go next.
Step 1: Read all codes and freeze-frame data, note the outside temperature when it set, and check for bulletins
IfA fuel pump module bulletin covers your vehicle
It meansHave the dealer follow it.
IfP018B is also stored
It meansCheck the pressure sensor reading first.
IfOnly P2635
It meansMeasure actual fuel pressure.
Step 2: With the engine off and fuel pressure relieved, check whether the scan tool pressure reading drops near zero
Warning:Fuel systems hold pressure with the engine off; follow the maker's depressurising procedure, away from sparks or flame.
IfIt still reads around 30-40 psi
It meansThe pressure sensor is faulty.
IfIt reads near zero
It meansThe sensor is plausible; measure pressure under load.
Step 3: Measure fuel pressure and volume under load against the service manual
Warning:Pressurised fuel is a fire risk. This is a job for a technician with the right adapters.
IfPressure or volume low
It meansDiagnose and replace the pump module.
IfPressure normal
It meansLook for injector or other restrictions.
Symptoms
- Check engine light
- Poor fuel economy
- Hesitation or surging, often in very hot or cold weather
- Misfire
- Engine stalls, or starts and dies Gets more serious: stop and have it checked.
Compare with: Check engine light with loss of power
How to fix
Step 1: Ask a dealer to check your VIN for fuel pump module bulletins; GM has published several for P2635 on trucks and SUVs.
Step 2: Note when the code appears (hot day, cold start, low fuel) and tell the technician; GM's fixes depend on it.
Parts and cost context
- Fuel pump:The pump is usually replaced as a module, sometimes with an updated part number under a bulletin. Labour varies; get a quote.
- Fuel rail pressure sensor:Rule out a sensor that misreads before replacing the pump.
Labor varies by vehicle and shop; get a quote before you approve a repair.
Compare used part prices on PartPriceGuideOn your vehicle
ChevroletYour car
2014–2017 · Silverado 1500
Supported by vehicle dataHot-weather vapor in the fuel feed line causes hesitation, surging or stalling with P2635; updated pump module. Also GMC and Cadillac. Whether the bulletin is still current is not verified.
2016–2017 · Colorado
Supported by vehicle dataFuel pump module replacement procedure when P2635 and/or P018B set. Whether the bulletin is still current is not verified.
2010–2018 · Silverado 1500
Supported by vehicle dataIn-tank pump whine and start-and-stall below about 20 F, with P2635 among the codes. Whether the bulletin is still current is not verified.
2014–2019 · Silverado 1500
Supported by vehicle dataP2635 with P018B can be a fuel pressure sensor stuck reading high. Whether the bulletin is still current is not verified.
17-NA-335Status unverified
Hesitation, surge or stall above 100 F with P2635/P018B
2014–2017silverado-1500, tahoe, suburban · issued · NHTSA 10190331
In ambient temperatures above 100 F, vapor can build up in the fuel feed line, causing hesitation, surging or stalling with P2635 and/or P018B; the fuel pump module is replaced with an updated part. Also covers GMC Sierra/Yukon and Cadillac Escalade.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
16-NA-225Status unverified
Replace fuel pump module if P2635/P018B set
2016–2017colorado, malibu, volt · issued · NHTSA 10113986
Procedure to replace the fuel pump module assembly if P2635 and/or P018B are set. Also covers GMC Canyon/Acadia and Cadillac XT5.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
18-NA-103Status unverified
Pump whine, start-and-stall or loss of power in cold weather
2010–2018silverado-1500, colorado, cruze, express · issued · NHTSA 10137540
Below about 20 F the in-tank fuel pump may whine and the engine may start and stall, not start or lose power, with P0087, P018B, P228A, P228B or P2635. Also covers GMC models.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
PIP5286BStatus unverified
P2635/P018B: fuel pressure sensor stuck reading high
2014–2019silverado-1500, tahoe, suburban · issued · NHTSA 10162136
P2635 with P018B can come from a fuel pressure sensor that does not read the low end; it still shows 30-40 psi after the system is depressurised. Also covers GMC and Cadillac trucks.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
Related codes
Sources and review
- P2635 Fuel Pump A Low Flow/Performance
- GM 17-NA-335: hesitation, surging or stall in hot weather with P2635/P018B; updated fuel pump module
- GM 18-NA-103: in-tank fuel pump whine below 20 F, start-and-stall, P0087/P018B/P2635
- GM 16-NA-225: fuel pump module replacement for P2635/P018B
- GM PIP5286B: P2635 and P018B from a fuel pressure sensor not reading low pressure
- Last reviewed
- Written by
- Saurabh K.
- Editorial review
- Pending
- Technician review
- Technician review pending
This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error