Fuel Pump B Control Circuit Low
The P2633 code means the vehicle's onboard diagnostic system has detected: Fuel Pump B Control Circuit Low. This is a critical severity code.
- Keep driving?
- No -- stop driving
- DIY difficulty
- hard
- Estimated cost
- $300 - $900 (parts and labor)
Best-selling code reader on Amazon. Reads and clears check engine codes on any 1996+ vehicle. Under $30.
Check Price on AmazonAffiliate link -- we earn a commission at no extra cost to you.
Essential for diagnosing sensor codes, checking voltage, and testing circuits. Under $15 and pays for itself on the first job.
Check Price on AmazonAffiliate link -- we earn a commission at no extra cost to you.
Common Symptoms
- Fuel pump B running at reduced speed
- Low fuel supply pressure
- Engine stalling under load
- Hard starting especially when warm
Probable Causes (Ranked by Likelihood)
- Short to ground in pump B control circuit Very High
- Fuel pump B motor winding failure High
- High-resistance connection at pump B connector Moderate
- ECM pump B driver pulling low Low
Step-by-Step Diagnostic Procedure
-
Measure pump B circuit voltage at connector
-
Check pump B wiring for short to ground
-
Test pump B motor current draw
-
Inspect fuel tank connector for corrosion
Frequently Asked Questions
Why does my engine stall only under heavy load?
At light load the reduced pump B output may provide enough fuel, but under heavy acceleration the demand exceeds what the weakened pump can supply.
Can a corroded fuel tank connector cause P2633?
Yes. In-tank fuel pump connectors are exposed to fuel vapors and can corrode, causing high resistance that drops the voltage reaching the pump.
Is pump B the same as the lift pump?
In many applications, yes. The lift pump or transfer pump (pump B) is the low-pressure pump that feeds fuel from the tank to the high-pressure injection pump.
Sources
This page is built from documented references. Verify against your own service info before repair work.
Explore More
Was this helpful?
Send this to whoever is fixing the car — your mechanic, or the person asking what the light means.