Question/Help from J-Spec/Euro E31 owners

[Staehling]

Hi guys,

I have a 1991 J-Spec 850i. Recently, I've been getting the CATALYST OVERHEAT error on the OBC/MID, complete with tone/beep, immediately after starting the car. Happens regardless of cold/hot, and this is not the quick 2 second one that J-Spec owners see that disappears right away.

The Euro/JSpec cars have after-cat temperature sensors, part numbers:
11 78 1 722 763, or 11 78 1 738 347. Don't want to throw parts at this, otherwise I would have replaced the sensors by now in hopes of it fixing it, but I would rather try and troubleshoot/diagnose this to make sure it's the sensors and not something else.

Anyone ever deal with this?

Info: 1991 J-Spec 850i, Automatic
-Just passed emissions testing recently with great results
-Air filters and sparkplugs are new, will be doing caps+rotors soon, but since the error comes on instantly, I do not believe this to be an ignition/rich issue
-Behaves the exact same way with both sensors plugged in, both unplugged, 1 unplugged, other unplugged.

thanks!
-Andrew

[Wuffer]

Was it giving you this error message before you changed plugs? What plugs did you put in?

[Staehling]

Hey Tom,

It was giving the message before I put the plugs in.
I used Bosch F8LCR as recommended by all.

It did not start appearing in synch with any maintenance I did.
Air filters had been done for a while before it started poppin' up.

Realized I had no CHECK ENGINE bulb, so I thought it might be in conjunction with an engine error I hadn't been seeing yet, but I put a bulb in and checked for codes, just 444 and the CHECK ENGINE doesn't come on, just the CHECK.

-Andrew

[Wuffer]

And the Catalyst Overheat error message on the OBC stays on?
I guess my next step would be to put new temp sensors in and see what that does. Dont think I have any here tho. Pretty sure they are on my #1 car and not connected. Not removing them tho so dont even go there. 8-)
See you tomorrow at WrenchFest in the Rain?

[Staehling]

The Catalyst Overheat message stays on after the bong/beep/tone...if I clear it by hitting CHECK, it returns after a few seconds. Will definitely see you tomorrow. Can I take a look under yours to see if they are in fact disconnected? Is your #1 Euro/J?

[Wuffer]

Nope my #1 (FrankenBimmer) is a hybrid - a Canadian Spec car with a J-spec engine, transmission, cats and engine controllers and a hodgepodge of other stuff.

[Staehling]

Very happy to report this has been dealt with.
At Wuffer's mini-wrenchfest , I was very fortunate to run into a fellow named Wayne who had had the same problem. By shorting the wires(proper term?) before the sensor, the therm sensor is effectively disabled, not reporting any error to the MID/OBC. Wayne and I were in agreement that these sensors don't seem to do a darn thing other than warn you about temperature...ie., the car still runs great when one of these sensors is toast.
Thanks to chromeowner for pointing me in the right direction initially, Wuffer for bringing the 8-guys together, and Wayne for sharing the simple fix.

[BryAg]

Staehling, can you talk about the 'shorting the wires' fix and how you go about doing it. Thanks

[zubbie]

Staehling, can you talk about the 'shorting the wires' fix and how you go about doing it. Thanks

Interesting. I was told by a BMW mechanic that this method does not fix the issue. This would be a much easier solution that I thought given how EGT thermocouples generally work.

[Staehling]

Hey guys, it definitely eliminated my persistent error.

It's a two-wire system, so I snipped the wire between the connector and the sensor itself, opened the sheath up, and connected the two wires together and tucked them away...not great at describing this so I'll try to get a picture next time I'm under the car.

Hope this helps.

[zubbie]

Hey guys, it definitely eliminated my persistent error.

It's a two-wire system, so I snipped the wire between the connector and the sensor itself, opened the sheath up, and connected the two wires together and tucked them away...not great at describing this so I'll try to get a picture next time I'm under the car.

Hope this helps.

good to know. I understand completely. On an E34 there is only one and it is very easy to see right after the cat. In fact there is a connector on the box frame where you can easily short the wires.

I learned something new. So much for BMW mechanics???

[Staehling]

good to know. I understand completely. On an E34 there is only one and it is very easy to see right after the cat. In fact there is a connector on the box frame where you can easily short the wires.

I learned something new. So much for BMW mechanics???

[BryAg]

Thanks a lot for the assistance fellas, will get under there and give this a looky. Cheers

[Staehling]

If you need a pic let me know

[BryAg]

Yeah, if you could post something, that'd be great. Thanks again

[boomer3]

I second that, i would like to see what you did before i begin snipping. Im getting the same cat overheat. I think i know what to snip/short out, but better to be certain first.

[Staehling]

I'm an ass for not posting this sooner, sorry to any who were waiting to see the pic.

[wokke]

I have since shortly the same damned error message but can't even find those sensors on my car. WTF are they?????????

[Wuffer]

They are located just behind the cats on the J-spec cars. There is a (far) simpler way to fix the issue, on the J-specs at least. In the rear E-box, there is one tall relay. Remove that relay and the message never appears. Has no apparent affect on anything else that we have noted thus far.

[wokke]

They are located just behind the cats on the J-spec cars. There is a (far) simpler way to fix the issue, on the J-specs at least. In the rear E-box, there is one tall relay. Remove that relay and the message never appears. Has no apparent affect on anything else that we have noted thus far.

That's what I suspected but no sensor at all. And the large relay in the trunk is non existing as well. Very strange. But I'm convinced I'll find the cause and fix it. Just a matter of time

[Wkarlwallace]

Hi, this is my first post. I’m trying to help a friend figure out if his 91 850i is a jspec. I have the car with me now. Nothing shows on the Carfax before 93.

[razman850]

Does it have 2 alternators?I think j-Spec had 2 alternators. Also turn on your high beams and see if the FTP turns on too.FTP is the high beam on the light strip in the bumper.

[DeltaSix]

To add to the above:

Automatic JSpec cars have the A-M-S transmission switch, rather than just A-M, beside the shifter in the center console

The low beam cutoff profile is for left hand driven roads. I.e. high on left slopped down to right.

The tool tray in the trunk has Japanese on it rather than German or English


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[DeltaSix]

Now that I reread your question the easiest thing to do to find out the build year is to put the VIN into realoem.com to get the build date.

Also: If you have carfax to 93, it’s highly unlikely the car is a JSpec as they didn’t start coming over until the late 2000s due to regulation. The carfax back to 93 implies it’s a US car, I believe.


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