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Symptoms of this problem could be a drop in acceleration due to an inefficient air/fuel ratio, or poor fuel economy. The most likely though is that the sensor itself is not functioning correctly. A value that is quite different could suggest a few problems. The sensor should display a temperature very similar to the air temperature in the workshop. Cold air is denser than warm air, so requires more fuel to maintain the correct fuel-air ratio. The engine system needs this data itself so that it can estimate the air density and then calculate the correct fuel-air mixture. The intake air temperature data lets the user know the temperature of the air that the engine is pulling in. Since the post cat sensor is reading “cleaned up” exhaust, the reading should remain steady at around 0.5V. The first sensor should be switching more often between rich and lean readings. However, if the pre-cat sensor reading is fairly steady at close to 1.0 volt, that indicates that the fuel mixture is too rich, while anything going towards 0.0V would suggest that the fuel mixture is too lean. Since the computer is constantly changing the air/fuel mixture based on engine RPM, it’s normal to see rapid fluctuations in the pre-cat oxygen sensor readings, from lean to rich. Of course, nothing is ever perfect, so you want to be looking for a fluctuation around 0.5V. If the air-fuel mixture is at the perfect mix, called the stoichiometric ratio, then you should get a reading of 0.45V.
Nissan data scan automatic transmission how to#
By monitoring the oxygen in the exhaust, the computer can determine how to adjust the air/fuel mixture.Īn OBD2 scanner will display the oxygen levels in terms of voltage. All cars made after 1996 are required to have two oxygen sensors. Oxygen Sensors show the level of oxygen in the exhaust stream before and after the catalytic converter. These are probably two good places to start looking if your OBD2 scanner reports strange idle RPM values. If your RPM is falling outside these ranges, then it’s probably down to an issue with a faulty or carboned idle control valve or electronic throttle body, or a vacuum leak. For cars, idle speed is usually between 6rpm, whild for trucks its around 600, and motorbikes are higher at between 12rpm.
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Unless you’re touching the throttle, this will be the engine’s idle RPM, which is what we want to check. Live data will also show your engine’s RPM. Either way, that high of a fuel trim means you should be looking for the underlying problem. Or, the computer is trying to compensate for lower than normal fuel pressure. like +25%, you may have a vacuum leak which is causing the computer to add more fuel. Readings outside of these ranges are an indication of engine or fuel system problems. Normal STFT values shift between -10.0% and 10.0%, while normal LTFT usually run between -5.0% and 5.0%. If short term fuel trim stay the same for a long period, the computer shifts them into long term fuel trim area. Fuel trims are also shown as Short Term Fuel Trim (STFT) and a Long Term Fuel Trim (LTFT). However, this is rarely the case.Ī reading that is above 0.0%, so a positive number, means more fuel is being added to the air/fuel mixture mixture, while a negative number means the computer is subtracting fuel from the mixture. A reading of 0.0% would suggest the fuel system is working perfectly that the correct amount of fuel is being released. Fuel trim refers to how much fuel is being released into the engine by the fuel delivery system.