P2636: Fuel Pump B Low Flow or Performance
What to do
The symptom is P2632's, in a milder and more intermittent form: hesitation or cutting out when the tank is low, and particularly when cornering, braking or climbing at the same time. Keeping the tank above half will largely avoid it.
Because it is intermittent, what you have noticed is the evidence. Write down roughly where the gauge was and what the car was doing each time, and hand that over — it is not something a workshop can reproduce on a ramp.
One thing worth mentioning: on many vehicles the transfer is done by a device with no moving parts, driven by returning fuel. If so, it has not worn out, and what needs checking is the flow that drives it rather than the device itself.
What this code means
The second fuel pump is running and not moving enough fuel. What that pump is for, and why a saddle tank needs one, is at P2632; the pressure-versus-flow distinction that governs testing it is at P2635.
This is the partial version of P2632's failure, and it is the harder one to catch — the transfer still works, just not fast enough to keep up. So the car does not fail at a predictable point on the gauge; it fails when demand is high and the tank is lowish and the fuel has sloshed the wrong way, which is a combination that may occur once a fortnight and never in a workshop.
On designs where the transfer is done by a jet pump rather than a motor, the fault is often not in the transfer device at all. A jet pump has no moving parts — it works by squirting returning fuel through a venturi to drag more fuel with it — so if it has stopped transferring, what has usually failed is the flow driving it or the small line delivering that flow. A part with no moving parts has not worn out, and that is worth saying before one is ordered.
Likely causes
Start here
- Faulty fuel transfer pump · moderate
- Blocked fuel pump strainer · moderate
- Restricted fuel supply line · moderate
Less common
- Weak fuel pump · moderate
- Debris or corrosion inside the fuel tank · specialist
- Low voltage at the fuel pump · moderate
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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