Subaru forester PO 171 code

PO174 &171- Both banks lean. This could be caused by a defective MAF or O2 sensor but something as simple as a vacuum leak could cause this problem. Also make sure there are no air leaks from the MAF sensor to the intake manifold. I have repaired many vehicles with these codes that was caused by a vacuum leak. Hope this helps

Type: OBD PO 171 --for the code discription,
cause & solutions

OBD PO 174
OBD PO 443

You did not list a vehicle, so here are the generic codes.
Code 171 is system lean bank one and code 174 is system lean bank two.
The computer is getting a signal from the O2 sensors saying the fuel system is too lean, and the computer can not make it rich.
Possible causes are low fuel pressure, vac leaks, EGR valve problems, and so on.

For 1999 Subaru Truck Forester AWD 2.5L MFI 4cyl the Oxygen Sensor is located under hood, center, rear engine area, mounted on catalytic converter.



Fig. Oxygen sensor location-Forester 1998-2002 2.5L SOHC engine (click over image for zoom).

Generally, Bank 1 is front and Bank 2 is rear.

Hope helps.

The 171 code is for the EVAP system and fuel.

PO 134 = 02 SENSOR CIRCUIT NO ACTIVITY DETECTED (BANK 1 SENSOR1)
PO 153 =02 SENSOR CIRCUIT SLOW RESPONSE (BANK 2 SENSOR 1)
PO 154 =02 SENSOR CIRCUIT NO ACTIVITY DETECTED (BANK 2 SENSOR 1)
PO 155= 02 SENSOR HEATER CIRCUIT MALFUNCTION (BANK 2 SENSOR 1)
PO 171= SYSTEM TOO LEAN (BANK 1)
PO 174= SYSTEM TOO LEAN (BANK 2)
I WOULD SAY YOU HAVE FAULTY OXYGEN SENSORS CAUSING THE ENGINE TO RUN TOO LEAN REPLACE THEM AND YOU SHOULD BE BACK IN BUISNESS

this is a code reflecting a faulty pressure contorl solenoid (A Electrical) a problem in your transmission. You will need to have this serviced by a transmission shop or your subaru dealer

171 and 174 mean not enough fuel po 300 multiple missfire could be not enough fuel 430 can be caused by bad ignition in the cat from not enough fuel // first thing borrow a freinds mass airflow sensor

http://www.automotiveforums.com/t473813.html

PO 171 is a system to lean code. This link will explain why this is and how to fix it,