Fuel Pump B Control Circuit High
The P2634 code means the vehicle's onboard diagnostic system has detected: Fuel Pump B Control Circuit High. This is a moderate severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- hard
- Estimated cost
- $200 - $700 (parts and labor)
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What Are the Symptoms of P2634?
- Fuel pump B running at full speed constantly
- Higher than normal fuel supply pressure
- Fuel system noise from tank area
- Check engine light on
What Causes P2634? (Most Likely First)
- Short to voltage in pump B circuit Very High
- Pump B relay stuck closed High
- ECM pump B driver stuck high Moderate
- Fuel pump control module failure Low
Can I Still Drive with P2634?
Short distances only. P2634 is rated moderate severity. Keep trips short and get it diagnosed soon rather than waiting for symptoms to worsen.
Frequently Asked Questions
Can constant full-speed pump operation cause issues?
Yes. Excessive fuel supply pressure can overwhelm the high-pressure pump and fuel pressure regulator, and the constant operation increases pump wear and noise.
What is a fuel pump control module?
Some vehicles have a separate module that varies fuel pump speed based on demand. It sits between the ECM and the pump, using PWM to control pump voltage.
Will P2634 affect fuel economy?
Slightly. The constant high-speed pump operation wastes energy and can cause excess fuel to recirculate, reducing overall system efficiency.
Mechanics Guide Step-by-step diagnosis
How Do You Diagnose P2634?
-
Check pump B circuit for constant voltage
-
Test pump B relay contacts
-
Verify ECM can modulate pump speed
-
Check fuel pump control module if equipped
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
Which Vehicles Commonly Get P2634?
- 2010-2020 Ford Mustang EcoBoost
- 2012-2020 BMW 435i
- 2011-2019 Audi S4
- 2010-2018 Mercedes-Benz E350
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