P0171/P0174 error code

[tmitty]

Both banks detect a rich/lean air fuel ratio. I replaced the fuel pump and filter (again). That fixed the hard starting but the Check Engine light is still on and the car idles rough...almost stalls, I thought it might just be air in the fuel line, but I put 100 miles on it since and it's not going away. Other possible causes are the MAF, bad/"heated" O2 sensor or an injector problem.

I have a custom cat-back exhaust...resonator removed. I'm thinking it might have "heated" the O2 sensor. I'd appreciate any advice before I dump any more cash into this money pit of a car.

[Marc]

My guess......much less backpressure with the cat back exhaust & no resonator might be causing this problem.

[tmitty]

The exhaust has been on for about a year. While I've had other issues before (cam sensor, broken timing chain), the idle has always been fine. I thinking I might have a small leak in or near the cat.

[tmitty]

Ok. There is a leak, but it's in the intake boot. Thank god for this website! It never would have crossed my mind that that little intake boot could split. I found a couple of posts on those trouble codes which suggested spraying some brake cleaner under the boot as a test. Sure enough it surged right up. I can also hear the air being sucked in there.

I tried to search for the boot replacement procedure, but nothing comes up. I know I have to remove the fuel rail and manifold to get to it. I would just feel more comfortable if I had step by step instructions. Can anyone point me in the right direction? I have a 2001 4.0

[ntrenn]

Welcome to the bad boot club....

You have to pull the intake manifold to change the boot. You're out about $65 in parts (boot and intake gaskets) at list and a couple of hours of your time.
There are a few around here that have changed them - I chickened out, but that was 5 years ago and I wasn't that brave yet. I'm told it's not too hard to do. The replacement has almost 80,000 on it, while the original didn't make 50,000.

[tmitty]

I changed the "plenum" boot and everything feels good again. My 'rora got it's balls back and the transmission feels so much smoother. The MAF sensor really messes with tranny if it's not getting the right intake. Thanks for your help. I posted the procedure for replacing the plenum in the "How do I replace a split intake boot?" thread.

[justmatt]

Thanks for all the info on replacing the boot. I did mine last night and it's running much better. However, after driving it today, the check engine light is still on. When I got home, I unhooked the negative battery cable for about 45 minutes. Started it back up, and the light is still on. Did you have to clear the code with a OBD tool? Or did it turn itself off?

[ntrenn]

To turn it off immediately, yes you need one of the readers.

If you truly fixed the problem, it will go off on its own after something like 40 ignition cycles without encountering the fault.

To be sure you fixed it, go out and do some WOT 0-60 runs....if the MIL flashes at you...you still have the problem (flashing MIL light means impending converter damage). If it's missing, you will feel it at WOT.

[tmitty]

My CE light took a day to go off...no OBD tool...just went off.

[justmatt]

Thanks guys. After posting yesterday, I realized that I had forgotten to re-connect the MAF. Doh! I'll give it another day or two, and see if the CE light will go off.

[benny2450]

Thank you all very much for the posts.

I just came across the same exact problem with my 2001 Aurora 4.0 at about 53,600 miles. It seemed to run oddly for about 8 months with some ill-timed transmission shifts, poor idling (especially at red lights), and inconsistent power. On rare occasions during idling it would suddenly drop RPMs, almost to 200, and nearly stall but would quickly compensate. It didn't seem like anything connected really until the check engine light came on after I accelerated quickly a few times on a drive in to work. Until this happened I had no idea what might be wrong, if anything.

The service center where I work read the codes which were P0171 and P0174. They cleared them and the CE light and the same codes came back a day later. We followed the instructions contained in these and similar posts to diagnose the plenum "boot" leak. Spraying brake cleaner on it stalled the engine while it was running.

By the way, so that it's in this post, P0171 means that the fuel system is too lean on Bank 1 and P0174 means that the fuel system is too lean on Bank 2. Apart, these codes mean altogether something different. The combination of these codes is what points to a vacuum leak and/or air intake problem.

Thanks to this post we were able to accurately diagnose the problem and I actually had my car to the dealer for a repair which wasn't anywhere near as expensive as some people indicate in other posts - $35.99 part and 2 hours in labor. Just getting the car back, I can already see a huge difference in decisiveness, consistent power, and it's idling well again.

Again, thanks to all the post contributors. You saved me, and I'm sure others, a lot of money and a lot of guesswork.

[Paulaurora]

i think its like chain of same problem i just fixed this issue on my aurora 2001 4.0 with 72,,000 on OD.

[tennesseerip]

I had the same problem and got good advice on this forum. See the thread-Codes questions. In last month.

[cap10america]

Add me to the list...

I inherited my parents 2003 aurora 4.0

Instead of checking the boot, I foolishly took my car to the local cadillac dealer. I told them about the rubber boot plenum, they stated it was a bad 02 sensor and bad wiring to the other bank.
A few days later, the light came back on. I checked it with my mini obd checker. Yep, same codes. Out of money and patience.

Today, I took it to a friends shop, he diagnosed it right on the spot(barely looking at it) as it is common problem. Sure enough, he sprayed carb cleaner on the boot and the car stalled right out. He also checked it with his pro scanner and got the same codes.

He ordered the gaskets and boot. I am getting it fixed in a few days. Should have went to him in the first place....

I will report back upon completion.

[cap10america]

It's fixed!

I took it into a friends shop. 

All repaired. My Aurora is roaring again.

Runs great now. Smoother acceleration and transmission shifts. It also idles way smoother. At idle, the engine was surging a little.


Again, the symptoms:

• Check engine light is on.
• OBD P0171 and P0174
• Rough idle (surging)
• degraded acceleration and performance
• Slight decrease in fuel mileage
• Slightly rougher transmission shifts

If your vehicle has these symptoms, get it repaired as soon as you can or, don't drive it. You risk ruining your car's catalytic converter.

[Paulaurora]

Unless its specific GM issue you deff dont wanna take your car to the dealer most of them dono the car well. Only one dealer in NJ and one specific mechanic i know who knows the car very well others have no clue they will just put parts and see if it will fix the issue. While you pay for all of it.

[cap10america]

I have been taking my Intrigue to the Cadillac dealer for oil changes. The 3.5 engine is a little more messy to do.

When I got the Aurora, it was serviced at the same Cadillac dealer. I have been doing all the maintenance on that vehicle except for water pumps in both vehicles.

They tried to fool me and I caught them red handed.

Thanks to this site and everyone's contributions, it made life easier for me with this vehicle.