: Codes - P0171 & P0174 96 STS



nitrous1
11-24-04, 10:35 AM
I've been trying to troubleshoot a recurring problem with my STS. Shortly after I had the fuel rail recall performed, my STS began displaying DTC P0171 and P0174 simultaneously (Fuel Trim Bank 1 and 2 Lean). I've gone thru the FSM and checked everything for vacuum leaks, air intake leaks, missing vacuum hoses, etc... - but I haven't been able to find much wrong. I did find a small vacuum leak where the intake meets the head, so I pulled the intake and resealed it - hoping that the problem would be fixed. Unfortunately, the codes are still setting on a somewhat regular basis. I only have trouble when I let the car sit at idle speed (like at a stop light) - as long as the engine is running above 1000 rpm, I have no problems. I hooked up my Tech 2 last night and began going thru all the sensor inputs and I found a few of them out of range. The TPS is reading .51 volts but the FSM says it should be at .60 volts at hot idle, the MAF readings were a little too low, and the IAC counts were way too low (9-10 and the FSM says it should be about 30 at hot idle). I'm sure that all thes problems are related but I'm not sure where I should start. I'm considering just replacing the TPS, IAC and MAF, but I really don't want to just throw a bunch of parts at it without really knowing what the problem is. Does anyone have any insight or tips?

Thanks,
nitrous1

Ranger
11-24-04, 11:37 AM
Just a guess here, but I would look at the IAC first. Maybe just pull it and clean it to see if that helps any.

nitrous1
11-24-04, 02:04 PM
Just a guess here, but I would look at the IAC first. Maybe just pull it and clean it to see if that helps any.


Thanks for the tip - I wasn't sure if I could do anything besides start replacing parts.

nitrous1

Ranger
11-24-04, 11:06 PM
I am not positive but I think it is a pintle valve that controls idle air similar to the EGR. Nothing to lose by trying.

nitrous1
11-27-04, 05:38 PM
I am not positive but I think it is a pintle valve that controls idle air similar to the EGR. Nothing to lose by trying.


Funny you should mention this. I found that one of the studs in the EGR valve was loose - the threads were stripped out. It seem that the dealership didn't install the new fuel rail properly. I did a temporary repair with a longer bolt and several washers, but I need to Heli-Coil the threads.

Logandiagnostic
11-28-04, 01:46 AM
I doubt the system was ever resetted after the fuel rail issue. I would try resting the sytem first by disconnecting the battery....



Logan Diagnostic
www.airbagcrash.com
www.ledfix.com

ellives
11-28-04, 08:07 AM
I doubt the system was ever resetted after the fuel rail issue. I would try resting the sytem first by disconnecting the battery....



Logan Diagnostic
www.airbagcrash.com
www.ledfix.com


Sheesh -- if that's the case it doesn't say much for the dealer....

Ells

Logandiagnostic
11-28-04, 11:37 AM
I should also add....PO171 and 174 together can sometimes point to a oil film contaminated mass air flow sensor. Rare....but it does happen...


Logan Diagnostic
www.airbagcrash.com
www.ledfix.com

nitrous1
11-28-04, 04:51 PM
I should also add....PO171 and 174 together can sometimes point to a oil film contaminated mass air flow sensor. Rare....but it does happen...

Logan Diagnostic
www.airbagcrash.com
www.ledfix.com




Logan,

The MAF was actually one of the first places that I looked. I used to have a K&N filter on the car and I was a little concerned about oil film on the grid. I cleaned the grid with electronic spray cleaner, but that did not seem to help anything.

I did disconnect the battery overnight to try and reset the system (several times actually), but the two DTC's kept coming back.

I took the car out for a test drive yesterday afternoon after fixing the loose EGR valve and I wasn't able to get the SES light to come on. I was monitoring the Short and Long Term Fuel Trim values with my TECH 2 while I was driving around. I was typically getting values in the 3%-8% range while driving, but the values (I don't remember whether it was Short or Long Term) would go up to 20%-25% if I let the car idle in park for a while. I left the car running in the driveway for about 20 minutes and the SES never came back on. I have been able to get the SES to come on in just by letting the car idle for 5 minutes in the past, so maybe I have made some progress.

Thanks,

nitrous1