Usually associated with a vacuum leak, thus causing lean fuel mixtures. Check every intake duct clamp and hose plus the vacuum lines and any rubber connectors.

P 0171 is the odd cylinders bank (in the V-engines)
P 0174 is the even cylinders bank

OBDII diagnostics. Trouble codes description for GM

OBDII/EOBD diagnostic code definition. More than 18000 codes for all autos. Trouble codes description for GM

obdii.pro

 

Take the cover off the top of the engine and look at all of the pcv hoses, all of mine fell apart around 70k miles.

 

I've checked all hoses and connectors, don't see any leaks or anything happening under the hood, so i'm stumped on what I should check next. Hoping I can resolve the problem on my own because the dealership is a pain to deal with.

 

Just had all 4 injectors replaced on my 14' 2.0T. OEM Delcos. After several years of monkey around with this vacuum line, that vacuum line, A/F sensor, O2, exhaust check (I do hv a ZZP), replaced coils, replacing plugs, injector cleanings. Everything was replaced and cleaned. NEW OEM cat. Most replaced by me. *Anyway, new injectors, not one misfire (if you've owned the car for sometime, you know what I'm talking about; intermittent stumble at idle). No more every once in a blue moon lean codes. Again, I repeat it has not misfired at idle one time in the past two weeks. Quite frankly, it should've been done when the car was new, but the dealer always told me they weren't finding any issue. I'm calling bullshit. I think that these newer injectors may have been updated. Shifts sharper under load. Always use high quality 93 octane. Purrrfect. I found a good private tech and I was able to get the parts relatively cheap. You're gonna need several gaskets and I had him replace the rail sensor and the crank sensor. Not a cheap job, it's 6 hours and they'll need to clean out the intake due to the direct injection residue. When he gave me the parts back, one injector looked pretty fouled up. Rail cleaning is great, but it's not always going to resurect these injectors because they're under such high load. Anyway, if you want it right, you have to bite the bullet. Most people I know just got rid of the car.

 

Get a can of throttlebody or brake spray cleaner solvent. With as much beauty plastic removed as possible, with the engine idling warm, judiciously shoot the air, intake, vacuum, PCV pipes, hoses, connectors, clamps with the spray. ANY idle quality change is a vacuum leak.

Takes patience and a tall scotch & water.

 

Dealing with this myself, copy that scotch and water.

Car seems to run ok, but long term fuel is at 30% short term erratic.

 

Car seems to run ok, but long term fuel is at 30% short term erratic.

Whats your MAF grams/second reading? Do the fuel trims straighten out under load?

There is a bulletin for certain year ATS cars where the intake manifold bolts back out. That could be your problem. Could also be 200 other things lol.

 

MD66, seems you have a scanner, you can test O2s as I posted here:

2013 ATS 2.0T rough downshifts when warm

So i just replaced All 3 PCV Valves, both of my PCV hoses, new air filter, cleaned my MAF with spray & i am still getting a p0171 code, could i possibly need to attack my O2 sensors next?What could my next step be? I only get the rough downshift when my car is warm, about after 30 minutes of...

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Sick, it's possible a connector to new O2s came loose or it was routed incorrectly and chafed or burned on exhaust. Possible one of the new O2s crapped out. If so, testing as recommended can tell. But with your symptoms does sound like a vacuum leak, so would have to hunt for it as posted by Sub.

If you are not up for above and your car is out of warranty, recommend asking around for a good independent shop.

 

Thanks guys, got some parts on order. Just got this car and don't know what has been done to it already. Upstream O2 sensor looks new. Going to replace a few things that are common problems and see what it does. I also have to replace the coolant temp sensor in the back of the block, won't that be fun. The Guage is reading erratic and sometimes codes for P0116 and disables the AC. Not sure if these problems are related or not.

 

Well, the ECM actually trims the fuel based on a lot of inputs, one of them being coolant temp. So if that sensor is bad, and it is the one the ECM uses to adjust trims, then yeah, it would be related.

 

The Guage usually reasd in the middle between hot and cold. When it fluctuates it goes near hot. I suspect when it codes it reaches hot. The scanner I was using to monitor temp, was reading from 215 to 245. Even 215 seems hot for normal light driving. The software on the scanner is for truck engines. Had to use the monitor for a 5.3. It won't read oil pressure, so I am skeptical about the coolant temp numbers. How hot is normal on a 2.0? My truck stays under 200 usually.

 

The PCM coolant fan control table of your vehicle does not even command the fan for 4% rotation, and that is at 193 F deg
Fan is only commanded for 71% rotation and that is at 235 F deg so no that is not overly hot, esp in hot weather

What must be fixed is the P0116 DTC - Engine Coolant Temperature Sensor 1 Circuit Range/Performance

PCM depends on ECT in part of its math, even when A/C can be ON

 

Replaced the coolant temp sensor and vacuum pump. Sensor was seeping coolant and vacuum pump was leaking oil. The coolant temp Guage reads cooler now and engine fan operation seems normal.

 

it was that expensive to fix that most get rid of the car!?

 

I have a P0171 code right now. I confirmed there were cracks in a PCV hose and ordered PN12673868 from Rock Auto for $119.79 excluding shipping and sales tax. I'm going to Harbor Freight tomorrow and picking up a set of fuel line disconnect tools to help with the hose's removal for about $4. Total cost is right around one hundred and forty bucks. I'll post up a thread with photos.