CEL - P0174 code

[Steck]

You very well may have developed a vacuum leak somewhere. I'd check to make sure you plugged everything back in after your latest round of changes. If the tune is off, those lean codes will show up well before 5000 miles. The other possibility is an exhaust leak near your O2 sensors. Based on the scenario, I don't think the tune is the issue.

[caverman]

It's funny you asked because I just found something this weekend which may or may not be the issue.

First off I will say that prior to this the CEL has been coming and going on a more frequent basis. Totally random, one min I start the car to go somewhere it's on. Then I leave that place and it's off. Then it might say on everytime for two days and then go away for a start or two.

So, at this point I decided I just need to have someone else look at it and maybe re-dyno/re-tune the thing (remember I don't have any tool to watch the fuel trims with). I was supposed to call the shop back this week to see when they could fit my car in.

In the meantime a good friend of mine that's really in to racing and cars (mostly Mustangs though) happen to come over this weekend. I started telling him the whole story as we were starring at the engine. He looks down and says "hey, that hose doesn't look like it's in a good spot".

The hose from my Halltech that goes over to the tube that's under my engine cover was sitting on the belt tensioner. It had fallen down some how and touched the top of it. I feel the hose and sure enough there is a pretty good sized gouge in it.

I'm not really sure this is the ultimate culprit only because the whole is not all the way through. I put my finger on one end and blew through the other and it seemed like it was holding air. I tried twisting it and moving it and see if it would crack open a little but it didn't.

I replaced the hose but the CEL was still staying on. Probably because it hadn't gone through enough cycles to clear it. I went by Auto Zone Monday and cleared the codes and the CEL hasn't come back on since. I'm keeping my fingers crossed that was the issue. If not I'll end up having to take in to have it put back on the dyno or something.

The symptoms sure act like it was sucking in air causing it to go lean. That also might explain why the CEL has been coming on more frequently. Over time the whole has gotten deeper and deeper into the hose.

In the pic below you can see the hose going over on top of the TB but if you can imagine it slipped down and was riding on top of the tensioner when my buddy saw it. However, you can also see that even though it put a good sized gouge in the hose it didn't go all the way through either.

[Steck]

It may have been inadvertently fixed when you replaced it. Reseating the fitting into the plug on the intake could have resealed a possible small leak. Believe me, it doesn't take much to cause trims to tank at idle. A pinhead sized hole can freak it out at very low airflows.

[1981DFA]

Good find. I would still have it looked at by the shop that did the tune just to make sure that the rear o2 sensors are turned off, and have them check the tune real quick. It should only take a few min. I would also go ahead and buy two new front o2 sensors and replace them. One at a time if you desire and then replace them both at the same time just because they may be not functioning correctly just becasue of all the problems that you have had here recently. This way they are fresh and new and you know your car will be running 100% correctly.

[caverman]

Originally Posted by 1981DFA

Good find. I would still have it looked at by the shop that did the tune just to make sure that the rear o2 sensors are turned off, and have them check the tune real quick. It should only take a few min. I would also go ahead and buy two new front o2 sensors and replace them. One at a time if you desire and then replace them both at the same time just because they may be not functioning correctly just becasue of all the problems that you have had here recently. This way they are fresh and new and you know your car will be running 100% correctly.

Re-tune will be a $200 and each O2 is $100. I do agree that taking it to be looked at and having it checked on the dyno would be the best but I don't really have an extra $400 to spare unless I really need to.....especially not a Christmas time with three young kids.

If the CEL comes back the steps you mentioned will be my next steps for sure.

I might pay the $200 to have it re-checked on the dyno in a couple months even if I don't get a CEL. It's just that I have higher than normal credit card bills this time of the year.

[caverman]

Originally Posted by Steck@Craven

It may have been inadvertently fixed when you replaced it. Reseating the fitting into the plug on the intake could have resealed a possible small leak. Believe me, it doesn't take much to cause trims to tank at idle. A pinhead sized hole can freak it out at very low airflows.

I wonder if the fact that the hose dropped down over the tensioner like that and with the way the tensioner had to have been pulling on the hose....maybe it pulled on the hose enough to cause a really slight leak where it connected under the engine cover (not sure what that hose is called...I'm assuming it's like the PCV?).

I didn't examine the hose and how it was connected or not connected. Once my buddy found it we just immediately looked to fix it. I just assumed the hole in the hose was the issue. It wasn't until I pulled it off and examined it closer that I realized it didn't go all the way through.


Thanks for everyones input!

[JusticePete]

CEL - P0174 code is a code we had programed into the 5th Gen. It activates when it detects anything but OEM or Pedders suspension

[caverman]

Ughhh.....

Well my CEL came back on again over the weekend. Took about 2 wks to come back on this time. Just regular everyday driving....no WOT or anything. I haven't checked the code but I'm sure it's the same thing (too lean). I'm kind of back at square one again.

Time to take it over to Andy at ADM to see if he can help me find it plus I'll see about having him put it on the dyno to check if it's actually running lean. If not then it might be a sensor. I might have him relook at the exhaust to make sure he thinks it's connected correctly. I did have the exhaust taken off back when I had my rear diff bushings put in. It's possible there might be a slight leak in there somewhere even though I've already looked over the exhaust and didn't see anything.

I have to take my car into the dealership in the morning to have them look at why my heated seats aren't working correctly. Hopefully that will all be squared away in one day. Dealership is probably not going to like that CEL too much. Once the car is out of the dealership, I'll schedule out my time with ADM and post up anything we find.

[Steck]

I'm sure it will easily be figured out. It is probably something trivial that won't take much time. Stuff like this happens! Good luck.

[caverman]

Update…..Looks like Andy @ ADM Performance figured out.

Long story short, after hooking up the car to HP Tuners Andy was able to see something was going on. He said my LT Fuel Trims were in the +25 range and that at +16 it would throw a CEL (at least that’s what I remember….hope I got that correct).

He checked over the hoses and connections to the CAI and things and all looked good. Eventually looking over everything he traced it down to my RX Catch Can was causing a vacuum leak.

There is a drain plug on the bottom of the can to allow you to drain it. Well, guess I didn’t get it tight enough or something the last time I drained it. With the car running you could put your finger over the bottom of it and hear the sucking/vacuum sound it would make. I tightened it up all the way and he reset my tune and unplugged/plugged in my ECM. Started the car back up and now the LT trims looked normal.

Took Andy about 30 min or so to find it and hopefully that’s the end of my issue. I probably would've never found that stupid leak.

Big THANKS to Andy!!!

I always love going into his shop to see the projects going on. I’ll tell you….Andy’s place is always the cleanest, most organized shop I’ve been to. I wish I could keep my garage ¼ as clean and organized.

[Steck]

I just had the same problem with another brand catch can on a Corvette. I figured it was a vacuum leak. Glad it is fixed!

[insomniac2k2]

I just had this same exact issue. Here's what was causing mine



Now im off to find that crappy mechanic that installed his CAI. Oh wait, that was m....

[geaux_tigerss]

Originally Posted by insomniac2k2

I just had this same exact issue. Here's what was causing mine



Now im off to find that crappy mechanic that installed his CAI. Oh wait, that was m....

This is why you limit your drinking while modding. A cold air should be a 6-pack or less job.

[insomniac2k2]

I do not recall seeing the California hazard sticker on engine compartment. I think i will sue for lost time drinking.