05 STS P0174 and P0171

It's your engine, transmission, driveline
kevm14
Posts: 13936
Joined: Wed Oct 23, 2013 10:28 pm

Re: 05 STS P0174 and P0171

Post by kevm14 » Sun May 05, 2019 4:20 pm

Guess what the other code was?

P0174, lean bank 2. Uh oh. Well that may explain why the light didn't go out like it usually does. Remember that thing I said about expecting the light to be on and then not scanning it which means there could be another issue present that I ignore? Yeah, that is this. And I have two scan tools.
20190505_135043.jpg
Freeze frame. Looks like it was at idle when the code set though the trims aren't like totally pegged but they are high. Bank 2 is considerably higher than bank 1 also.
20190505_135254.jpg
20190505_135258.jpg
Not really expecting this I gave the engine bay a cursory visual inspection. I retorqued the intake bolts. Only the front driver's side moved. The other nine were tight.

However I found a disconnected breather tube. It draws metered air from the air intake into the driver's side valve cover. Now bank 2 is the driver's side. Maybe this was the issue? It should have effected the whole engine but clearly this is supposed to be connected. I disconnected it when I did the air filter on 4/20. Looking at my P0430 thread, the light came on a day later on 4/21!! Then it went out on 4/23 and also came back on that same day. It has been on since. I am optimistic that with the unmetered air leak fixed, the light might actually stay out long enough to get inspected. I do have a burnt out passenger side fog light but I didn't get the bulb yet and they may not care about fog lights. There is also the tint but hopefully I get somebody cool again.

kevm14
Posts: 13936
Joined: Wed Oct 23, 2013 10:28 pm

Re: 05 STS P0174 and P0171

Post by kevm14 » Mon May 06, 2019 5:52 am

No light but I should have grabbed my generic scan tool to monitor fuel trims on the way in. I am not 100% sure the trim reset "took" with key on engine off, despite issuing the command.

kevm14
Posts: 13936
Joined: Wed Oct 23, 2013 10:28 pm

Re: 05 STS P0174 and P0171

Post by kevm14 » Thu May 09, 2019 6:13 am

kevm14 wrote:No light but I should have grabbed my generic scan tool to monitor fuel trims on the way in. I am not 100% sure the trim reset "took" with key on engine off, despite issuing the command.
Right. So I did grab my generic tool and drove in with it. Trims look as they were before, which means:
* +/- 2.5% or so during most driving conditions
* Long term does go up under vacuum conditions, with bank 2 higher than bank 1. Like up to 10% or so. I would suppose this is either valvecover or intake gaskets just being old. Nothing I am going to rush to fix as it is within bounds but that is why it set a code for bank 2 with that hose disconnected as it pushed it out of bounds.
* Said it before but with the wide band O2s doing fuel control, this thing seems to stay in closed loop all the time. I will have to look at it more but it seems to stay in closed loop under overrun and also heavy throttle. The trims looked good under heavy throttle.

So...trims seem back in bounds even if there is an underlying issue that sometimes pushes the trims under vacuum, particularly bank 2.

kevm14
Posts: 13936
Joined: Wed Oct 23, 2013 10:28 pm

Re: 05 STS P0174 and P0171

Post by kevm14 » Thu May 09, 2019 7:56 pm

Came up to a red light, and was in front, so I quickly hooked the scan tool up and loaded fuel trims. I launched at WOT and according to the two fuel status PIDs, it stayed in closed loop the whole time. The short term trims were doing something though I couldn't tell if the long term trims were.

I also noticed that the generic stream has a large amount of data elements. Like it has the fuel "equivalency ratio" aka lambda ratio. It shows 1.000 in normal driving, sometimes dipping slightly below to like 0.999. Under more throttle I saw it dip further rich and finally at WOT it read like 0.871 or something which would be somewhere in the 12.8 range in terms of AFR.

Seems to run a little better with the hose connected also...

Post Reply