The Mazda 626 was always dubbed “The Family Car” in Mazda’s lineup. It actually replaced the 616 and RX-2 in the late 1970s, and Mazda continued production until 2002. Starting in 1996, like all other production automobiles, Mazda integrated a new level of onboard diagnostics – known as OBDII-- into the powertrain control module. This new system not only made it easier for the PCM to determine faults early on, but also gave repair technicians a way to determine what the fault might be. This code is applicable for both the 2.0-liter four-cylinder and the 2.5-liter V-6 engine.
P1131 means that the front oxygen sensor detected the fuel mixture is too lean when the engine is at operating temperature, and the vehicle is traveling at cruising speed. This condition must be detected twice for the check engine light to illuminate and the trouble code to be stored.
A lean fuel mixture can be caused by a couple different scenarios. The most common is an air leak after the mass air flow sensor. Even a small amount of unmetered air can throw off the fuel mixture enough to set this code. Check the engine vacuum lines, air intake system and PCV system. You’ll likely find a disconnected or damaged vacuum line, or a bad intake manifold gasket. The other possibility is low fuel pressure. This can be caused by a faulty fuel pump, clogged fuel filter or a pinched fuel line.
