Hey all! I've got a bit of a conundrum. As some of you may know, my Disco has sat for a little over a year and I've just gotten it back on the road. The exhaust was not on it for pretty much the whole time I got the exhaust back on it and O2 sensors hooked back up and it's throwing codes for no readings on on any of the four O2 sensors or their heater circuits. I'm getting irregular misfires also, I'm assuming because of this.

I have cleaned the plugs out, both sensor end and harness end, with MAF cleaner. I replaced both front O2s with new Bosch units, which the old one's weren't very old. When that didn't work I tried brake cleaner followed by MAF cleaner. It seemed like I got a bank 1 sensor 1 reading for a while, but by the time I was a couple miles down the road it was missing again and getting zero voltage.

I'm going to crawl under it again tomorrow and see if oil has dripped back into the plugs, but I don't think it would've done it that quickly. I've cleared the codes a couple times and they keep coming back, though this is the only time I've watched the live O2 data.

I'll get some more info tomorrow when I clear the codes again. I'll also try running without any O2s plugged in because it seemed to be running fine when it didn't have any exhaust on it. That said I also never had it out and about at speed when they were unhooked. Only puttering around the neighborhood once every couple weeks to try and keep her loose.

I have checked the fusebox under the hood and all fuses and relays are fine, so that's not the issue. The O2 wiring, what I can see of it, is fine. That said I haven't checked it with my multimeter yet because I'm not sure which prongs are supposed to do what on the harness end of the plug.

Really just looking for any ideas or a general pointing in the right direction because I'm pretty much at a loss. Thanks guys!

 

Did it work before you put those headers on?

 

Your ECU may not be reading them if the car sat without being hooked up to battery?

 

ZG, I had the headers for about a year before I parked it and it ran fine with them.

Matt, it did sit for some time without a battery hooked up, but not sure why that would make a difference. ECUs sit on shelves for years and still work fine when hooked up. Being inside the truck wouldn't make any difference, right?

 

I seem to recall reading here on more than one occasion about ECU having to "re-learn". I have given up on Bosch O2's and have gone to the Walker ones that AB sells.

 

Alex, you are bound to get endless wild speculation. You are on the right track with the multimeter. The plug pinouts are in the ETM. Be sure not to bend the pins open too much when testing or else you will add a secondary problem to the mix.

Adam

 

Very interesting. I'll see how they act when I clear the codes again. I was going to get the walkers, but the Bosch were the only ones I could get at Advance next day.

I guess I'm gonna also test the old sensors I pulled with my multimeter and a torch to see if they are in fact working.

Does anyone have the pin out for the O2 plugs?

 

The O2's ground thru the ECU I have read of people having problems with it not grounding them correctly. So they cut the 4 black ground wires at the ECU plug and ground them to the chassis inside the kick panel.
I sure you can check this with a meter.
I also had a problem with one of mine not reading and it turned out to be inside the big grey connector near the under hood fuse box.
One of the connectors was corroded.
Mine was the wire that was brown with the pink tracer. Most of the sensors use this and for some reason the drivers side front O2 was a separate wire back to that connector were everything else was in another brown/pink wire on the connector?

 

Here are the Pin Outs...Go NUTZ!!!!

 

Drivers Front
.03v on pin 1
12v on pin 2
.64v on pin 3
.19v on pin 4

Front Passenger
12v on pin 1
12v on pin 2
.63v on pin 3
.18v on pin 4

Both Rears
.03v on pin 1
12v on pin 2
.63v on pin 3
.19v on pin 4

Both front O2 sensors measured 2.2 ohms cold.

One rear O2 sensor read 2.3 ohms.

One rear O2 I already knew was bad, no continuity.

I just pulled the ECU out. I cleaned all of it's plugs and all the connectors in that kick panel with MAF cleaner. I'm going to clear the codes and see if there is any change now after I reconnect the O2 sensors.