Is it the oxygen sensor?

The check engine light has just come on on my 1991 240. When cruising on the highway the car "stumbles" and slightly loses power. The spark plugs are not fouled and the throttle housing is clean. The TDC sensor was replaced 4 months ago which solved the hard starting problem.

Would it be likely to be the oxygen sensor? This is where my Haynes manual tends to point.

Is this an expensive part to have replaced?

Can a 2nd hand part be used?

Thanks,
Ben

[Mike_Brace]

What fault code is being displayed?

Mike

[classicswede]

It is possible to test the lambda probe with a multi meter. You should see a flutuating voltage between 0.1 and 0.9 volt (0-1volt lambda) on normaly the black wire from the probe. Normaly if the probe is buggered you get a fixed 0volt fixed 0.5 volt or even a fixed 1 volt.

My 91 240 has had a similar problem. We know that the oxygen sensor is bad but the car runs fine most of the time. However, it has stalled twice on the highway. Removing fuse #4 and leaving it out will allow it to start. This is the fuse that powers the tank fuel pump and the sensor. Sometimes the car does not start with the fuse in and removing it and leaving it out allows it to start. After it has started or maybe a few days later the fuse is reinstalled and starts fine. This doesn't make sense. Any input?

I have had an 89 240 run horribly on the freeway and not run at all in idle to mid-range rpm because of a malfunctioning O2 sensor. The car ran with a very rich fuel mixture.

It is not an expensive fix if you use the 'generic' sensor. I have installed a sensor that was taken out of a Lincoln in my 240 and it ran perfectly. Testing with a multimeter is the way to go. A $20 multimeter and a $40 02 sensor beats a $80 tow fee and the repair on top of that. Elsey