'92 240 Check Engine Light

Hi Larry,

The info I have suggests that with a 2-1-2 code, the cause of the fault is more a "wiring fault to the heated O2S sensor". Perhaps you should check or replace the wiring. Incidentally, what symptoms do you experience when driving the car? Has the fuel consumption risen?

Good Luck. Andy I.

This code means that the computer is not happy with the signal (i.e. signal voltage is too high or low) from the oxygen sensor. Since a new sensor hasn't fixed the problem, then just about the only other problem can be a bad connection. My guess is you have a problem with the sensor ground. Measure the voltage between various ground points and the battery negative terminal. Check all the ground wires, especially the one from the back of the valve cover and firewall, but don't ignore the connection from the negative cable and engine block, or even the connections at the battery. And it's even possible that the exhaust system has become electrically isolated from the engine and you may need to run a ground wire directly to the oxygen sensor body. Later cars have a signal ground wire built into the oxygen sensor that is connected to the computer, just because of this problem. And just to make it interesting, the problem may be intermittent, making it much harder to find.

Thanks everyone for the info. I'll try cleaning the battery connections and the ground connections this weekend and see if that helps. Larry