![]() Over time, the carbon will build up inside the valve and make it stuck. The idea is to reduce the engine temperature and control NOx emissions. Stuck open EGR valveĪn exhaust gas recirculation (EGR) valve basically takes a little bit of exhaust gas and puts it back in the combustion chamber. If the number you got on the scanner is much lower than the actual number, it’s time to replace a new coolant temp sensor. You should be able to see the coolant temperature live data.Ĭompare it with the actual number you have using an infrared thermometer. To know if the coolant temp sensor is bad or not, use the “Live Data” function in your OBD2 scanner. In this case, the ECU thinks that the engine is not hot enough, so it continues to pump the rich mixture to the combustion room, causing your car to run rich. In case it’s bad, it will keep saying to the ECU that the engine is still cold even though it has already warmed up.Īs I said before, a cold engine needs a rich air-fuel mixture to run properly. The coolant temperature sensor tells how hot your engine is. Read more: How to test an O2 sensor with an OBD2 scanner? Faulty coolant temperature sensor Don’t worry, replacing these sensors is very easy and cheap! In that case, you should clean them first. If you get any of the codes below, the MAP or (and) MAF sensors can be bad. But when the engine gets hotter, it really doesn’t need that much fuel! In this case, they’re saying that “so much air is coming.” In fact, it’s not that much!īut the stupid ECU believes it anyway and sends the signal to pump more fuel, causing the engine to run rich.Īgain, when you start the engine cold, a rich air-fuel mixture is good enough. The idea is that no matter what happens, the engine control unit (ECU) always wants to achieve the perfect air/fuel ratio.Ī faulty MAP or MAF will send the wrong data to the ECU. ![]() MAP and MAF sensors are responsible for calculating how much air the engine is taking in, which determines how much fuel should be injected. The below are the causes that make your car run rich. P0172 and P0175 are the DTCs that generally tell you the system is too rich. In short, a cold engine likes running rich, but a hot engine doesn’t. When things get to the normal operating temperature, this fuel-air mixture must lean out (less fuel) to the perfect air/fuel ratio: 14.7:1įor some reason, the rich mixture keeps being rich, and a warmed engine can’t burn it efficiently, causing your car to lose power, idle rough, hesitate during acceleration, or even stall. ![]() A cold engine needs a rich mixture (too much fuel, not enough air) and a high RPM idle to function correctly. ![]()
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