The Complete Engine Code P0171 Troubleshooting Guide

My 2005 mustang GT's check engine light came on yesterday. The 2 codes were P0171 and P0174 which are lean codes for bank 1 and 2 of the ... The P0171 trouble code indicates that your vehicle's engine runs too lean on bank 1. This means the air-fuel mixture contains too much air and not enough fuel. P0171 almost always points to a vac leak. Clamp the line to the bleeder valve under the intake. It's a very common failure. It could be lean under high load/demand conditions and fine at low load. Mixture lean/rich codes can't set until the O2 sensors are active and ... To diagnose P0171, see the Possible Causes below. Check fuel pressure. It should be about 55 psi (380 kPa). If it idles OK, try 'power braking' ... P0171 is for a lean mixture. The O2 sensor is detecting too much air/oxygen. This causes engine computer to open the injectors to stay open longer to add more ... Code P0171 stands for “System Too Lean (Bank 1)”. This diagnostic trouble code can happen for a number of reasons related to combustion inside your engine. The ... Code P0171 indicates Bank 1 of the engine has a lean fuel mixture. P0174 indicates Bank 2 of the engine has a lean fuel mixture. The most common cause that we see at the dealer is a MAF sensor, especially if you have a K&N or other oiled air filter. O2 sensors can also ... P0171 and P0174 are codes for a lean condition. This is usually caused by a vacuum leak. Sometimes it is caused by a faulty oxygen sensor, but ...