Recently I took my 2005 Dodge neon. 2.0 to get an emisission.. To my surprised I failed miserably. Or what I thought was miserably...I recieved three codes which are p0700,p0731,p0720...This explains the crackle noise I would sometimes hear while driving. I also experienced my car reving up before switching gears...Upon relaying this message to my mechanic, his automatic response was that I need a new transmission that will cost me well over $1000. Please HELP me with any thoughts or suggestions...

 

P0700 means there is a DTC stored for the transmission. P0731 is Incorrect Gear Ratio in 1st Gear. P0720 is Output Speed Sensor Circuit Malfunction. The output speed sensor malfunction could [very likely] be causing the incorrect gear ratio, and both will trigger the check engine light and the P0700 code (obviously). It could be the sensor (likely), but the wiring should also be checked to make sure no wires are broken or grounded out. If there's bad wiring, a new sensor won't do a thing. Most any mechanic will automatically want to replace or rebuild a transmission whenever there's a problem with it. Drives me crazy, and really kind of annoys me.