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)
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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
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.
Mechanics Guide Step-by-step diagnosis
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
Sources 2
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
- Cross-checked against the SAE J2012:2002 DTC table (2026-08-27)archived scan of the SAE standard — readable copy, not SAE’s current edition
Commonly Affected Vehicles
- 2010-2020 Ford Explorer EcoBoost
- 2012-2020 BMW 328i
- 2011-2019 Mercedes-Benz C300
- 2010-2018 Audi A4
Related Codes
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