The EVP sensor is an emission system component found on certain vehicles. It is a part of the EGR system, the emissions system that recirculates exhaust gases back into the engine to reduce cylinder temperature and NOx emissions. The EVP sensor monitors the position of the EGR valve so that the computer can adjust it according to operating conditions. [When the sensor fails] it can cause problems with the functionality of the EGR system, which can result in increased emissions. Usually a bad or failing EVP position sensor will produce a few symptoms that can alert the driver of a potential problem that should be serviced.
1. Poor cold start performance
One of the first symptoms of a potential problem with the EVP sensor is poor cold start performance. If the EVP sensor fails it can send an incorrect signal to the computer, which will affect the flow of the EGR system. Improper EGR flow may cause engine performance issues, such as difficulty starting, rough idle, and even misfires, which may be most prominent at cold starts.
2. Check Engine Light comes on
Another symptom of a potential problem with the EVP position sensor is a Check Engine Light. If the computer detects an issue with the EVP position sensor or circuit it will set off the Check Engine Light to alert the driver of a potential issue. The Check Engine Light can also be set off by a wide variety of other problems, so having the vehicle scanned for trouble codes is highly recommended.
3. Failed emissions test
A bad or failing EVP sensor can also result in a [failed emissions test]. If the EVP positions sensor malfunctions and affects the functionality of the EGR system this may result in an increase of NOx emissions. For states with strict emissions requirements, the vehicle may not be able to be registered until the issue is fixed.
The EVP position sensor is an emissions component, and any problems with it can result in the vehicle failing an emissions test. For this reason, if you suspect that your EVP sensor may be having an issue, have the vehicle inspected by a professional technician, such as one from YourMechanic, to determine if the issue should be replaced.
This article originally appeared on YourMechanic.com as Symptoms of a Bad or Failing EVP Position Sensor and was authored by Ed Ruelas.