Pre-Cat Fuel Trim Lean AND Rich?!
 

I have a '06 3.0i. It was about 20 degrees F. The SES light came on and has been on for the last week. I ran it with an Actron Scanner...two codes showed up:

P1092 Pre-Catalyst Fuel Trim Too Lean Bank 2
and
P1093 Pre-Catalyst Fuel Trim Too Rich Bank 2

Why is it both? I have an appointment with the mech next week, but was wondering if it was okay to drive as it is now. Any help is appreciated. Thanks!

Did you ever get this sorted? I've had P1092 before but never had both P1092 and P1093. Now I've got it. I've replaced the intake air boot which was cracked as well as popped in a new Siemens/VDO MAF. I drove around for a week and the SES light never went off. I cleared it with my scanner and it came back the following day. I'm lost.

I read a couple of posts on here and on Bimmerformums and I've decided to go the fuel system cleaner route a la dirty injector. I'm currently running 2-11oz cans of BG44K through. Hopefully this will clear it up.

Car runs great. Only thing I'd say is there's a very faint miss during idle but you would probably never notice it unless you're staring at the Tach with your ninja eye. Even gas mileage seems unaffected. On a recent road trip to Toronto and back, I averaged 21.3MPG with the family and some luggage and things in the back.

Oh sorry, I did not see that anyone repliedto the post. Um...it turns ot the gas I was putting into the X was the wrong kind.

Now before people start assuming that I was putting in normal unleaded...I was not. Actually I thought the station was top tier when it was not. I switched stations and voila, no more SES forever...

It's OK - I didn't expect you to reply since the thread was a year old! But thank you anyway. It seems that when the P1092 and P1093 appear together, it's somehow fuel-related. I'm hoping by the end of this fuel system treatment that my issues will be resolved. We shall see.

I've since swapped both Bank 1 & 2 pre-cat Oxygen sensors and hoping to see if the light comes back on in the other bank. That would make it easy and i'd just replace the stupid o2 sensor, even though it's only a year and a half old.

Light came back on. HELP!

I've swapped the O2s and the same P1092 & P0193 codes came back on. So it's something on Bank 2. Plugs?

Once again, the P codes have failed me. The P codes were wrong. After taking it to the indy last week, he hooked it up to the GT1, pulled the BMW codes which were 235, 236. This translates to Pre-Cat Bank1 & 2, too rich. After explaining that I've replaced the air intake boot that was cracked and the MAF, he said the only other thing he can think of, was the spark plugs. I have NGK Iridiums in there and he suggested going back to the OE plugs. So I told him to button it up and I'll come get it. It's been a week now, and I haven't replaced the plugs, but since he cleared it, the light hasn't come back on! So strange man....

That week turned into 2000 miles and the light came back on, with the same codes. Strangest problem I've ever dealt with. I've since replaced all coil packs, crank position sensor and switched to using BMW OE oil (thinking compression). My next items are cleaning the ICV (read about this on a few diff forums with relation to the P1093 code) and pulling the injectors and cleaning them.

How about you try the plugs as the indy suggested. You do know that not all NGK iridium will work in our cars? You actually have to cross ref the part numbers very thorough to make sure you get the right ones.

Thanks for the reply. I did actually pop in the BMW OE NGK's back in May but that didn't do the trick. :dunno:

Well too rich means too much fuel is hitting the O2 sensors. That means either you are leaking fuel, or not burning it all.

Since you did coils, plugs, and maf, I think you should get the injectors out, maybe rail.

How is your fuel mileage?

Oh, have you cleaned your throttle body ever? How many miles on the car? Maybe your TB plate is sticking, and the computer compensates by dumping more fuel.

I would agree. You seem to know your stuff. And that's precisely the path I'm headed down. I'm going to pull the IAC this weekend to soak and clean it out in the event not enough bypass air is getting through during deceleration. I also picked up a fuel injector rebuild kit which includes the new o-rings, pintle cap and injector filter. So this weekend the rail is coming off. I've had it pressure tested at the rail and it's 50psi so that's about right.

Fuel mileage is decent. I get 19.2 combined. Last time I reset the consumption values was about 3 weeks ago and it's been about 50% city and 50% highway since. I've always found it to be very accurate after a few weeks of driving.

When you take out the IAC, clean the hell out of the TB. Clean the plate as well. Really only two things left for you to do.

I think you will have to reset the ECU. I believe these codes do not clear on their own.

I have cleaned the TB and IAC but not since I first bought it and replaced the OSV/PCV/Cyclone Separator and did a major 60K tune up albeit at 86k. Car now has 145K on it. So seems as if it's almost time for another 60K tune up.

Finally broke down and took it to the dealer. They sent the info off to BMW as the tech and foreman couldn't make sense of it. BMW came back and said the data depicts the car taking too long to get to operating temperature thus running rich. They suspected a thermostat leaking internally. I'm going to do a partial cooling system refresh (coolant temp sensor, upper and lower hoses, water pump & thermostat) and see how that plays out.

As for the short trip scenario, the explanation was that while cold, the DME is in agreement that the engine should be running rich and upon those few starts, sees no problem. It isn't however until a longer trip when it determines that it's been running rich for too long and throws up the code.

Follow up
 

As a follow up to this, I replaced the thermostat, water pump and aux fan switch o-ring as well as did a full cooling system flush. This did not resolve the problem. I haven't since invested any more time in trying to figure it out. I figure come time for inspection I'm just going to have my wife do a couple short trips as usual and when the light goes off, drive it over to the inspection facility and it should pass. :)

I am still concerned however that I'm probably damaging my cats and perhaps not getting the best MPG I could get (although I get 20.1 combined).

Wow you did a lot. Well I can't really think what else it can be. Maybe check if you bulbs are ok. Lol. How is the thermostat on your car. Mine has a sensor on it that gave me an error saying it got stuck open. It actually told me thermostat temp is below coolant temp. Replaced it and all good.

As far as your situation, I think it's some sensor screwing you. Let's back up. That maf you swapped, is it OE BMW?

The MAF was not OE as in, stamped with the BMW logo, but it was however a Siemens VDO MAF which is stamped on every BMW MAF. I have since swapped back in the original MAF as that didn't resolve the issue.

I agree with the sensor thing. On my last long distance road trip (~300mi) I was monitoring the coolant temp with the unlocked cluster. At certain times it will dip down to almost 20c below and slowly crawl back up. 20c is ALOT IMO especially considering i'm at 80MPH at cruise control. It didn't seem to matter whether I was going uphill or downhill. I couldn't correlate it to increased load or a period of little load. There is an engine block/coolant temp sensor otherwise known as the dual temperature switch that I had planned on replacing until I could never get to the darn thing. You need to cut your spanner in half and even then it would be hell to get the leverage to break it loose from the block. I was definitely going to take it to my indy to have it done. I have the part - just never replaced it. But that's one consideration.

You might as well get it done. You got this far already.

I really can't think of anything else.

Thanks man - I really appreciate you pondering on this along with me. It's been a LONG battle with this prob. My original indy and BMW couldn't figure it out without wanting to take the shotgun approach and throw parts at it. I have a new indy now and hopefully if I get desperate enough, I'll take it to them. With the amount of bimmers this guy turns around and his return customer satisfaction, I have a feeling he'll figure it out.

hey, i am having the same issue as you do this time. and i cant figure out what's wrong, did you have urs solved?
i have 06 x5 3.0I
my first engine check light was bank 2 running lean, bad o2 sensor(upper stream bank 2), this diagnose and repair was all done by dealership($600 parts and labor), i replaced bank 1 upper stream o2 sensor myself afterward. figured it out it may go bad soon.

second time engine check light was bank 1 running lean. i had found that the intake elbow boot had a leak, so i had it replaced. problem solved.

last month i tried to start my engine, it ran very rough and was shaking really bad, engine check light came right on, it was the spark plugs, i had them replaced, and the light cleared(it was misfire), the old plugs came out to be very dirty.

the light came on again after few weeks i changed my plugs, it calls Catalyst Fuel Trim Too Rich Bank 2.
i checked all coils they work fine. checked intake runner valve, it has decent resistant when i was trying to flap. my next checking list will be fuel injectors, down stream o2 sensors, fuel filter and MAF. do you think my cat got damaged due to the bad plugs?

For me the solution was the Crankcase Vent Valve. I replaced it but the replacement was defective. It also melted one of my O2 sensors.