Hello all,
I may need to diagnose (locate) a potential vacuum leak in my C6. I'm getting a P0172 error code from my OBD II scanner and "vacuum leak" is one of the potential culprits. Any good advice as to where or how best to start running this down? Thank you--any advise would be greatly appreciated.

 

I have had good luck using carb cleaner. With the engine running, spray it around all the vacuum lines/fittings. When the engine stumbles you have found the leak.

 

 

Thanks for the input--I've seen that method used. I appreciate the help.

 

Thanks for the feedback. Yes--it is definitely showing P0172--Sys too RICH in BANK 1. My scanner will show an O2 sensor graph, so I'll look into it. I'll pull the info and get back to you. BTW--I did just put two BRAND NEW O2 sensors in yesterday--the two before the CAT CONVERTER mounted into the exhaust manifolds. I was hoping that would clear the CHECK ENGINE light but it did not. Do you think it may clear itself after a few days of driving? My OBD II scanner won't allow me to clear it either. It says there is an error when trying to clear it. So, I'm still searching for the reason I'm getting this P0172 code. I need to start looking for a possible vacuum leak I guess. I think I'll try spraying a little carb cleaner around first. I would appreciate any more input you can provide about how best to fix this issue.
thx

 

 

I have a SEEKONE SK860 OBD II scanner. Yeah--when I try to clear it it fails. I'll try it again and let you know. I'll get it out more today. Thanks so much for your help.

 

 

got it. I'll get back to you. Thanks again.

 

 

 

OK--I got the DTC P0172 error cleared--however, it required me to clear it while the engine WAS RUNNING not OFF even though that's what the devise said to do. The CHECK ENGINE light went out and I re-scanned the system and found no DTCs. Again--I cleared it while the engine was running--not with ignition ON and engine OFF. Clearing the DTC wihile the engine was running worked. Attached are a series of pics I took of the scanner while I was attempting to clear the error. Image-1 is the initial MONITOR STATUS screen I get upon selecting DIAGNOSIS. Image-2 shows the DTC. Image-3 shows the PENDING FAULT CODE light and the PERMANENT FAULT CODE lights lit-up on the devise. Image-4 shows the RICH TO LEAN SENSOR figures and Image-5 shows LEAN TO RICH SENSOR figures. Images-6-9 are DATA STREAM screens I shot too--after the DTC was cleared. I don't know if any of these are helpful or not and I've been unable to access any graphs showing TRIM data you mentioned. I'm not real familiar with working with an OBD II scanner and what it's telling me. BUT--currently I have two BRAND-NEW O2 sensors installed and I've been able to clear the DTC error. All this doesn't mean my worries are over as the CHECK ENGINE light may return. If it does, do you think I'm looking at a faulty fuel injector?
Thanks again for all your help.

 

Thanks for the pics !!...looking at your fuel trims you have BOTH banks running rich. Your total fuel trims on bank 2 are -28.2 (-5.5 + -22.7)...you should have gotten a P0175 also. That leads the diagnosis in another "direction"...You might have an "over reporting" MAF sensor because of a dirty OR defective one...a dirty throttle body is something to look at too...I'd clean both and we will go from there. You can check for a dirty MAF by running the engine at 3000 RPM...if the fuel trim numbers go from negative (yours) to positive numbers it's dirty !!...I don't see any MAF PIDS in your pictures but you should be reading between 4-7 grams/second at idle to 190 or more at WOT. Your MAP sensor with "key on engine off" should be around 103 kPa (14.93 psi). I'd also look at your air filter too. These numbers are for an LS1 engine. I don't know if you have a CAI or OEM factory. Like I said let's run it a little on the road and see if those fuel trims get better. I'll include a pic of mine at IDLE with PIDS I look at. Also I'll include 2 videos on fuel trims which are excellent. Matt is a microbiologist by trade and is SUPER SHARP. If you REALLY want to learn this stuff and not have to rely on forum members you can start here. Learning O2 sensor operation and fuel trims are the KEY to successful engine diagnosis...another thing, I'm looking at your Bank2 Sensor 1 O2...is it always .065 mv and not fluctuating between .065 and .900mv....065mv is SUPER LEAN ??....that's why I don't like looking at snapshots because I only see the number the camera captures while it's switching high to low...if I can see a graph like the picture of mine I sent you I have an idea of what's really going on.
h

 

Hello again Rwobs777--
I have already cleaned the MAF sensor twice before I installed the new O2 sensors. I will be driving my car most of the week, so I'll keep you posted on any more news or progress. Thanks for the video links--I'll check them out.
Thanks again.

 

 

Hello rwobs777,
Update. I went 3 days--driving my car each day for around 24 miles per day before triggering the CHECK ENGINE light--again. After another scan, now I'm getting a P0175 DTC--Rich on the Right Bank. I've cleanined the MAF sensor twice now and have cleaned it again after seeing this. So, after already replacing both 02 sensors, it looks like the MAF sensor is the problem. Is that what you think? I need to see what the MAF sensor value is--I did not check that.
thx--let me know.

 

Hi !!...yes, let me know what your MAF values are at idle and snap throttle...do those fuel trims go positive under load ??...if this happens it's more than likely a bad MAF... now where did you see about this DTC being caused by a vacuum leak....well, if that what it says check for it.... what do the long term trims look like on the left bank ??...remember if the left bank is just below the value that it sets the DTC doesn't mean it's ok !!....is your air filter clean or has it been cleaned ??...that will cause negative fuel trim numbers...also I'd clean the throttle body. Do you have a fuel pressure gauge to check pressure at the fuel rail ??...if it's above 62 or so at idle (LS1 numbers) it can mean a failed fuel pressure regulator which is part of the fuel filter assembly. So, check left fuel trims, vacuum leaks ??, clean the air filter, check fuel pressure. A more rarely seen condition is a stuck open EVAP purge valve...on the LS1 it's on the left hand side and the hose goes to the intake manifold right behind the throttle body...if the EVAP canister is maxed with fuel vapor and the valve is stuck open it will pull those fuel vapors into the manifold and there goes your fuel trim numbers way negative. That's about it for now !!....is the 0175 the only current DTC...any in history ??...is the car running ok under idle, cruise and WOT ??