SOURCE: emission problem o2 sensor/egr valve?
Codes do not tell you what is wrong. They only tell you if there is a problem with a specific system/circuit.
From the information you have given it sounds like you might have a problem with the EGR valve which is causing the O2 sensor codes. There is no way to tell for sure but this is probably the most likely cause of your problem.
Here is a website that has a lot more information along with videos about how different sensors work:
http://www.myautorepairadvice.com/obd_codes.html
SOURCE: 2000 Hyundai Accent failed the emission test, high
Did you RESET the Adaptives?.. if you didn't that may be the problem. To reset adaptives, remove both battery cables and touch the cables together for 30 seconds (60 seconds is better), then reconnect the cables to the battery -- see if that cures it. You are correct, there is no EGR valve on that engine. However, there are several other sensors which could be causing your problem.. one is the MAF, the other is the MAP and still another is the IAT and the ECT (MAF - MASS AIR FLOW, MAP - MANIFOLD ABSOLUTE PRESSURE, IAT - INTAKE AIR TEMP SENSOR and finally the ECT- Engine Coolant Temp Snsr. If any of these sensors is malfunctioning,& lying to the ECM, they could cause a 'LEAN' fuel condition and that's why your NOx's are high.
SOURCE: Fails the NO ppm test in 1999 cavalier. Already
A couple of things; you can't have any leaks in the exhaust system, in front of the cat, and you must have the correct mixture going into the engine. The cat must have at least .45% CO going into it in order to reduce NOx. Make sure you have the correct fuel pressure, good fuel filter, and the engine is not running too hot when you take the test. In fact you may want to try a cooler thermostat. The oxygen sensor is only a fuel trim device, the bulk of the systems fuel control is dictated by the MAF and MAP sensor if it has one. Bottom line; your engine is running too lean or there is air getting into the exhaust system before the cat. You may want to try another MAF sensor if you know the other factors are good. If you have access to a gas analyzer, drill a pre-cat hole and check pre-cat CO under load, at least .45% is critical.
SOURCE: been parked for a year
either reset the computer or get a diagnostic scan to find the problem. the check engine light on doesn't mean it won't pass inspection
SOURCE: my 1997 Dodge Intrepid failed
Your faulty O2 sensor can create EGR problems. Start with just replacing the O2 sensor and see if the rest self corrects.
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