Sunday, August 12, 2012

BMW 325i Base 2.5L, L6, Trouble codes P0300, P0171 and P0174

2001 BMW 325i Base 2.5L, L6, MFI, DOHC, Eng Desg M54, Siemens MS

MILEAGE:  181,000

Customer Concern: The check engine light is on. Trouble codes P0300, P0171 and P0174 are present.

1. Check for an intake air leak in the throttle body, intake runner gaskets and Positive Crankcase Ventilation (PCV) valve. The best time to check for intake leaks is when the engine is cold, as the gaskets tend to seal up as they expand after warm up.

2. A smoke machine can be used to check for leaks, or the intake area can be pressurized with regulated shop air to 10 PSI. Then spray around the throttle body with soapy water and look for bubbles.

3. Check the PCV system by testing the crankcase vacuum. It should be from 8 to 15 millibar (that equals about 1/4 to 1/2 PSI of vacuum). It can be checked at the oil dip stick tube.

Potential Causes:

Leaking PCV Valve
Air Mass Meter (AMM)
Restricted Fuel Injectors
Insufficient Fuel Pressure
Intake Runner Gaskets.
Leaking Positive Crankcase Ventilation (PCV) System
Leaking Secondary Air Injection (SAI) Check Valve
Leaking Throttle Body

Confirmed Fix:

Replaced Brake Booster Vacuum Supply Hose
Tech Tips:
Common areas for leakage on the engine are vacuum lines, cracked intake boots and around the crankcase breather or the breather itself.

BMW 325i Base 2.5L, L6,  Trouble codes P0300, P0171 and P0174 are present

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