Hyundai check engine light question:

My Hyundai check engine light problem came when I got this fault code P0133 rear oxygen sensor not switching. This vehicle is a 1997 model and has an OBD2 automotive diagnostic system. Based on the vehicle mileage, this car has too many miles and I decided to change the rear oxygen sensor including the catalytic converter (Cat). After doing all of these, the check engine light returned with the same fault code. I am now thinking of replacing the ecm (engine computer) but since it is too expensive, I want to ask a 2nd opinion..

Hyundai check engine light ATS Fixes:

For starters on this Hyundai check engine light problem, you can replace the ecm as long as you do the following tests:

1.) check all the wiring ground connections for the engine sensors using ATS wiring diagrams supplied to you. Pay particular attention to the oxygen and mass sensor ground wires which have a common connections. Look for corrosion and signs of looseness. If possible, remove the ground connections and have it cleaned. Once you have serviced all these ground wires, reset the fault code and take the vehicle for a road test and see if the code goes away. If not…

2.) measure the ecm ground voltage readings with key on engine off. Again using the ATS wiring diagram, verify the ecm voltage at the ecm terminal. It must not exceed 0.250 volt. Higher reading means a fault in the wirings or component like sensors I mentioned above. You can also check for reference voltage (usually 5 volts) at pin 59 which is a good indicator if your ecm is good or not. If all the readings to the ecm ground wires are normal, check also the ecm power supplies. When testing the ecm, measure the voltage with ecm connected and disconnected. If you are still getting the fault code and both ecm ground and power supply are normal, it is safe to say that the ecm is defective.

ATS Tips:

You can get a one on one online assistance from a licensed mechanic if you are a member of ATS. For any other Hyundai check engine light questions, please leave your comments below. (ATS will answer all queries). Thanks!