Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Circuit/System Description
Idle Mode
During certain engine operating modes the engine control module (ECM) calculates an adaptation factor to adjust the fuel pressure regulator 2 set point pressure with the actual fuel pressure. The adaptation factor is the fuel pressure regulator 2 learned current that is required to maintain the desired fuel pressure at idle. This is done to adjust for manufacturing tolerances and aging of components. If the ECM calculates an adaptation factor outside the minimum or maximum calibrated limits, DTC P0191 is set.
Post Drive Mode
During post-drive mode, the fuel pressure regulator 2 relieves any remaining fuel pressure from the rails. After a 30 second bleed-down, the fuel rail pressure sensor should read atmospheric pressure and return the proper signal voltage to the ECM. If the signal voltage is outside of the specified limits, DTC P0191 is set. When this DTC sets in post drive mode the engine will be in Reduced Power Mode on the next key cycle.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.