Check Engine

[lobodude45]

I purchased a 1998 M3 coupe last month with 70,000 miles and I got a check engine light the other day. Did a OBDII code read and got the follwing messages:

Catalyst effeciency below threshold, Cyl # 4-6

Misfire detected, Cyl #5

Cleared check engine light but still unsure of code meanings.
Any suggestions?

Somebody suggested a bad 02 sensor or perhaps a dirty fuel injector in Cyl 5.

Car seems to run well still, Plugs and boots were changed last year. It happened after I washed the car of all things.....could cylinder have gotton wet. I did not wash inside the engine compartment.

Any help would be very welcome.

PS: Also have gotton brake light circuit error on computer occasionlly
and heard this is a common problem with E36 BMWs. Any comments on this would also be helpful.

[blkongry]

Well, washing the car actually can have a pretty big impact on what you describe. For one, the misfire code could be (and probably is) caused by water settling in down your sparkplug well... it's causes some arcing. I had that happen on my exgirlfriend's E30. It should just dry out.

Now, as far as I know on the OBDII, I think you have two O2 sensors... one in the front of the exhaust, and one on the rear (post catalytic converter)... the catalyst reading is probably related to a higher level of hydrocarbons coming out of the exhaust and the sensor back there thinking the catalytic converter isn't as effecient as it should be. That is such a quirky thing because it could be a moisture issue skewing the reading, or something temperature dependant. Did you get the error once you started the car after letting it sit for a while, and after you washed it? Once you let it heat up and drove it around for a while, have you got the code again? How thorough of a washing did you do? Could you have sprayed down under the hood somehow? Was it a machine car-wash?

I would just keep an eye on the check engine light and see if that pops on again. I think you probably just got some water somewhere that the car didn't like. If it comes back with the same code again and again, let us know.

As for the brake light circuit error, I'd go with what BMWCowboy always suggests and that is that the brake light switch is becoming problematic and needs to be changed out. It should be a pretty easy and cheap fix.

[Wayne 962]

I agree - run it and see if it happens again. Too coincidental with the car wash...

-Wayne

[Metroporter]

I too, have the same annoying problem with the brake light issue. After doing some research, I have found two different opinions. The first one suggests that there is a faulty relay switch underneath the steering column. Supposedly, there has been a recall on these little things. Replace this switch and you'll solve the problem.

The other opinion I have found is that the OBDII is very sensitive to the brake light circuits. If you replace any bulbs in the system (as I have), you'll have to make sure they match the original ones or replace all of them at once (I only replaced one). A difference in resistence from bulb to bulb will cause the OBDII to display the message.

Since the problem is intermittent and it does not effect the car in any way, I have not made time to play with either of these ideas. It may be that the switch that is overly sensitive to the circuit(?) Good luck with the other issue!

Silver '97 328i 4dr w/ sport pkg.

[Wayne 962]

That's a good thought, but I think the brake light circuit problem is independent of ODB-II. I have an ODB-II laptop scanner, and I can't recall any info on brake lamps in there. I'm not sure that circuit is part of the OBD-II implementation on the BMWs, but again, I'm not sure...

Corrosion and other debris can cause poor connections between bulbs, particularly if you live near an ocean area. One good way to eliminate problems is to remove all the bulbs and holders and to clean them with a stiff wire brush. That is what I would try if I was having this problem...

-Wayne

[blkongry]

Ironically, right after getting your note I read an article in my new Car and Driver about the new Mazda RX-8. It was getting the same type of code showing up on it, and it was a brand new ride. I think the Mazda showed it as the catalyst performing below specifications, too. Anyhow, the dealership just blipped the ECU with an updated program and sent them on their way. Over the span of a few hundred miles it came on again, and the dealer reset it again, then it came on again... finally it turned out the catalytic converter crapped out on them.

I highly doubt this is what is happening on your car, for the Mazda's run rotary engines with oil injection (meaning they actually purposely burn some of the oil), and that can clog the cat if the system isn't tuned right. The cats on our Beemers rarely go bad (but it is possible). The reason i tell the story of the RX-8 is because of the dealer's response... very casual and not a major concern. So many things, such as moisture, can trigger this code. As mentioned before, just keep an eye on it and I think you should be fine. Oh yeah, and the fact that you sprayed water up under the under-carriage really makes me think it's just water related and will dry out. You may have got some water down in the o2 sending unit, and depending on how many deposits are in your water where you live, it could be somewhat conductive and skewing the reading. Again, not a major concern.

As far as the brake light circuit, Wayne has put you on the right track. I'm pretty sure the circuit either senses resistance in the circuit, or load, but either way corrosion will cause a high resistance or an unbalanced load, triggering the circuit hazard lamp. You can change the brake switch, clean the bulbs, and make sure they are all quality lamps and that they all match. That should solve your problem. If not, then you may have a frayed, contacting wire somewhere. From what I've read on here, it could be under the trunklid in that harness that Wayne described... it's always good to check!!