'89 240DL Oxygen sensor problem
 

I could use some advice troubleshooting an oxygen sensor. Sorry for the long backstory, just trying to give as much info as I can.

When I picked up my 240 in March the O2 sensor was unplugged and the car threw a 2-1-2 check engine code. Makes sense, but it seemed to drive well enough. I plugged it back in, cleared the code, and took it for a drive. Within 15 minutes the engine light was back on and it was running like crap. Poor idle, shaking, hesitating from a stop. When I got home I had 3 engine codes (MAF, O2, lean mix). I pulled the battery for an hour to let everything clear before taking it for a drive again. Sure enough all of the codes and poor driving were back in under 15 minutes.

I unhooked the O2 sensor again and it went back to driving like when I picked it up. It felt kind of tired and it didn't get great mileage, but it's a 25 year old car so I didn't think much of it and ordered a new sensor, which I replaced yesterday. It's the splice-in style from Bosch and looked exactly like the one I removed, minus the complete/factory wiring harness. I spliced it in (100% sure it was a good connection and the splice is protected) and did the rest of my maintenance for the day (oil change, flame trap, throttle body) and took it for a drive. It ran smoother, quieter, had more power and seemed to be using less fuel. No check engine lights.

Within 100 miles the light came back on and the code was another 2-1-2, no other codes. The car seemed to still be driving as well as it had been all day, but I'll see today if there's a performance drop or any other issues come up. I probably put 20 miles on it last night after the light came on again.

Thoughts and advice? The lack of other codes and issues gives me some encouragement but I'm not sure what my next move should be.

Is there a reason you did not buy the direct replacement O2 sensor instead of a universal one. The poor performance is related to the ECU going back to safe settings because it is not seeing correct levels from the O2 sensor. Unfortunately you would need to replace the O2 sensor with the OEM or equivalent one. Most of them look the same but have different values.

I went with the splice-in version because it was significantly cheaper than the one with the harness. I'm fairly certain that it is the same sensor, just without the full wiring harness.

Did the place that sold you the sensor say it was a replacement part for your engine/car. It is hard to tell if this unit will perform the same as OEM.

Yes, it was specifically stated that it was compatible with my car. And, since it's a Bosch part, it should be OEM specs.

Take a look at this thread. Sounds very similar to yours:

https://volvoforums.com/forum/volvo-...-sensor-56280/

Thanks, I'll try some things from this thread. I reset the light before heading out yesterday and the light never really came back on, but it did flicker on and off for a second or two a couple of times. Maybe I'll luck out and it's a poor fuse connection. I've been meaning to Deoxit the fuse panel. I'll be sure to clean the O2 sensor connection, too.

if you have the tinned (silver/grey) fuses, I'd replace ALL of them with brass/copper ones, like you can get on ebay sold as Mercedes W123 W124 fuses (those are the Merc E series, like 300E, 300D, from the mid 70s to mid 90s), AND clean the fuse contacts. I use a soft clean pink pencil eraser to clean electrical contacts, that polishes off any oxide without stripping off the gold plating, and a touch of deoxit never hurts!

Thanks, Pierce! I'll be sure to do that, too. Sounds like a Saturday afternoon project.