Car Scanner OBD2 Elm327

5 Most Common Car Diagnostic Codes

Here are the five most common diagnostic codes you will likely experience at some point during the lifespan of your vehicle.

1. OXYGEN SENSOR

CODES: PO171-P0175

One of the most common car problems involves a faulty oxygen sensor. A vehicle’s oxygen sensor monitors the amount of oxygen in the exhaust so the engine computer can adjust the fuel mixture to maximize fuel economy and minimize emissions. If your oxygen sensor isn’t working properly, your gas mileage will increase or in some cases your car will randomly stall.

2. ENGINE MISFIRE

CODES: P0300-P0305

Mechanics work on engine misfires on a daily basis. If your engine is misfiring it means that one or more of the cylinders isn’t working properly. If your car is vibrating or shaking while idling and your car isn’t as fuel efficient as it should be, then you might have an engine misfire problem. The OBD-II system tracks engine misfires by monitoring the speed of the crankshaft when the engine is running. The OBD-II system logs a misfire when it detects a slight loss of speed in the crankshaft.

3. EVAPORATIVE SYSTEM

CODES: P0411, P0440, P0442, P0446, P0455

The evaporation system (EVAP) is responsible for containing and removing vapors that are produced when fuel is burned. A loose gas cap allowing fuel vapors to escape from the fuel tank can often be the reason for setting off this trouble code. EVAP includes vent hoses, a charcoal canister, a purge valve and a pressure or vacuum sensor.
4. EXHAUST GAS RECIRCULATION (EGR)
CODE: P0401
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The exhaust gas recirculation, commonly known as EGR, controls the engine’s emission of smog-causing nitrous oxides (NOx). EGR recirculates part of an engine’s exhaust gas back to the engine cylinders. The car’s computer system opens and closes valves to recirculate the engine’s exhaust gas. Problems occur if the oil hasn’t been changed in a while or the car takes many short trips because the car isn’t allowed enough time to warm up, causing carbon buildup.

5. CATALYTIC CONVERTER
CODE: P0420, P0430

The downstream oxygen sensor monitors the catalytic converter. According to Wikipedia, the catalytic converter is “an emissions control device that converts toxic gases and pollutants in exhaust gas to less toxic pollutants by catalyzing a redox reaction (an oxidation and a reduction reaction).” The converter can become contaminated and increase tailpipe emissions if the engine is burning oil or leaking coolant internally or is worn out from age.
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Next time the engine light turns on you should feel confident knowing that it is likely one of these emissions control codes.

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