I got the SES light and cleared the code. Its come back on a couple times and so I read it and it indicated that it was the passenger side 02 sensor in front of the cat. I cleared the code again, and replaced the sensor. Only now the SES light came on right after I replaced it? what gives? I dont have a scanner so I'll need to borrow a friends again.
So even after replacing your
oxygen sensor, the light turns on again? Replacing the sensor is a short-lived solution to the problem. The light turns on because the sensor detects that the engine is not meeting the proper voltage. The battery supplies electrical power to run the vehicle, but it also controls and stabilizes system voltage. Whenever you’re diagnosing a “Check Engine” light, it is important to start by having the battery tested. An automotive computer is like any other computer; proper input voltage is critical. A bad battery can cause problems in electrical and electronic parts including the computer. It can even cause a “Check Engine” light.
Next, test the alternator and pay close attention to the condition of its diodes. An alternator produces alternating current (AC), but cars work on direct current (DC), making a conversion necessary. Because some vehicle sensors normally produce AC signals for the computer, a false AC signal from a bad diode (“garbage in”) can make your computer produce faulty output signals (“garbage out”). The computer can’t distinguish between an AC signal from a sensor and a false one from the alternator. This can lead to rough shifting, performance problems, codes, and, yes, a “Check Engine” light. In this case, the “Check Engine” light and codes would probably be false.
