Fuel System - MIL ON with DTC P0171/174

SOURCE: Mitsubishi Tech Talk Article March 2004

TITLE: CHECK ENGINE LIGHT ON WITH DTC P0171/174

APPLIES TO: All Models

SERVICE TIP:

If the check engine light illuminates and the PCM stores DTC P0171/174, check the following;

1.Freeze Frame Data. Does the freeze frame data indicate a long fuel-trim (LFT1 or LFT2) in the high percentage range of 5% - 12.5%? This high percentage could indicated a lean condition. Check the following:

Vacuum leaks (loose hoses, bad brake booster diaphragm, damaged injector O-ring, etc.)

Fuel pressure regulator for low fuel pressure.

Leaking exhaust manifold gasket(s).

2.Fuel Type. Some areas of the country use fuels blended with ethanol. The amount used can have some impact on the oxygen concentrations in the exhaust system, which can affect the PCM's O2 readings. If a customer is using fuel with ethanol, MMNA recommends that they change to another type of fuel to see if the condition improves.