Help with PO171 Error Code

mb522

Original poster
Member
Apr 3, 2012
7
Hello All,
I have been repeatedly been getting that pesky PO171 error code on my 2006 Ascender with the 4.2 engine. and around 60,000 miles. The following is what I have done so far, in order.
1. Had dealer re-flash ECM with latest version upgrades (free under open campaign).
2. Clean air box, and replace air filter.
3. Add Techron fuel injector cleaner to gas.
4. Clean MAF Sensor (with appropriate solvent) with battery disconnected for a ECM relearn.
5. Remove throttle body & thoroughly clean (with appropriate solvent).
6. Replaced the upstream Oxygen Sensor with a new AC Delco one.
7. Add 2nd Techron fuel injector cleaner to gas.

It should be noted that the truck runs & idles fine, accelerates with no hesitation, and at this point in time the only code it keeps throwing is the PO171 (after around 50 miles of driving).

I ordered a secondary air injection solenoid check valve & gasket which I heard can sometimes contribute to this error code. The valve should be here in a couple of days. Do I need to use gasket cement with the new gasket, or can I install it DRY?

Any thoughts on this situation would be greatly appreciated. I am determined to eliminate this PO171 error code without bringing my truck to a mechanic!

Thanks:crazy:
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
mb522 said:
I am determined to eliminate this PO171 error code without bringing my truck to a mechanic!
Why? Many independent mechanics are competent and honest and can save you money over wasteful shotgunning, which is my personal opinion about swapping the SAIS check valve. I'd pull and clean it first, and bench test it, if I was on a low budget. Only if it was stuck open, which is a trivial thing to spot visually, would P0171 be a result. Pulling the hose from the SAIS pump to the check valve would tell you on a cold start if the valve needed work or replacing.

A good high end scan tool could look in the Freeze Frame data after a P0171, and tell you the exact operating conditions that were present when the code was set. The fuel trim numbers may contain a clue. Looking at the O2 sensor data may be useful, as well as the MAP sensor data.

Fuel pressure may be an issue if the code sets more often during high speed driving than idle or city driving. Vacuum leaks are also mentioned in the shop manual as something to look for.
 

07ChevyTruck

Member
Dec 5, 2011
774
I would check your vacuum advance hose. It may not be attached all the way and that would toss a P0171 code. It has happend to me twice. Once by some one elses error and the other time was mine.
 

MichEnvoyGuy

Member
Dec 3, 2011
522
IME, cleaning MAF sensors can be a crap shoot. When they go bad, they're bad. A skewed MAF would set a P0171.

Roadie is right, you need a scan tool that reads live data so you can monitor the O2 sensor and the fuel trims. They dont cost much anymore these days.

I had a bad problem running lean too. My issues were solved my doing a few different things. But heres what helped bring me back to a more stoichiometric mixture:

* Replace the throttle body gasket ($3) and make sure the throttle body is tight

* Check tightness of the intake manifold bolts

* Check tightness of exhaust manifold bolts

These are the first three cheapest things you can do. Any time air sneaks into the engine, even a small amount - can skew your mixture and set a P0171.
 

Bhaasie

Member
Mar 15, 2012
9
For the last two months been dealing with p0171. Driving me nuts... Ltft are hight at idle 14-20 after 19 sets dtc. Will be following this thread.

I've done so far:
Maf
Intake bolts tightened
Verify sais closing
New tb gasket
Tb bolts torqued to spec
Intake gasket replaced
Fuel pressure at key on engine off
Fuel pressure at engine idle
Gm fuel cleaner x3 at 20.00 a bottle
Injector cleaning at dealer
Tb clean

I am ready to drive off a cliff :hissyfit:
 

tricguy007

Member
Dec 7, 2011
131
Get a scan tool and a can of carb clean those r my best friend when fighting a lean code
 

Bhaasie

Member
Mar 15, 2012
9
I tried using propane around intake manifold, tb... no changes on my scan tool live data or engine speed. Will try carb cleaner. Also this weekend gonna do an old fashioned smoke test. (any brand of cigar better than others for smoke test :thumbsup:)

Will update as I continue to troubleshoot. My ltft is high only at idle, so I'm leaning towards vacuum leak somewhere. Down around 4-6 diving with rpm's up.
 

07ChevyTruck

Member
Dec 5, 2011
774
Bhaasie said:
For the last two months been dealing with p0171. Driving me nuts... Ltft are hight at idle 14-20 after 19 sets dtc. Will be following this thread.

I've done so far:
Maf
Intake bolts tightened
Verify sais closing
New tb gasket
Tb bolts torqued to spec
Intake gasket replaced
Fuel pressure at key on engine off
Fuel pressure at engine idle
Gm fuel cleaner x3 at 20.00 a bottle
Injector cleaning at dealer
Tb clean

I am ready to drive off a cliff :hissyfit:

First off don't drive it off a cliff. You will get very very injured.

Have you tried replacing the vacuum advance hose. It maybe rotted. :cool:
 

Bhaasie

Member
Mar 15, 2012
9
07ChevyTruck said:
First off don't drive it off a cliff. You will get very very injured.

Have you tried replacing the vacuum advance hose. It maybe rotted. :cool:

No I haven't. Where is this vacuum advance hose located? Does it run into throttle body?

Thanks... No cliff yet, I'll keep trying to fix this.
 

Bhaasie

Member
Mar 15, 2012
9
A few more, unsuccessful I might add, trouble shooting steps taken.

Sealed off oil dipstick hole - no change
Sealed off oil filler hole - no change
Disconnect Evap line from TB replaced with vacuum gauge - no change vacuum @ 22
Looked under truck, dropped spare Evap lines and canister all look good

Leaning towards weak or bad fuel injector or weak fuel pump/ pressure reg on fuel sending unit...

I recall a little metal flap on fuel filler neck, no longer there could it be in tank blocking flow? Also I don't get the woosh when I open gas cap as I used to?

Me right now = :crazy:
 

07ChevyTruck

Member
Dec 5, 2011
774
Bhaasie said:
A few more, unsuccessful I might add, trouble shooting steps taken.

Sealed off oil dipstick hole - no change
Sealed off oil filler hole - no change
Disconnect Evap line from TB replaced with vacuum gauge - no change vacuum @ 22
Looked under truck, dropped spare Evap lines and canister all look good

Leaning towards weak or bad fuel injector or weak fuel pump/ pressure reg on fuel sending unit...

I recall a little metal flap on fuel filler neck, no longer there could it be in tank blocking flow? Also I don't get the woosh when I open gas cap as I used to?

Me right now = :crazy:

I can see why you are going :crazy:.

The vacuum advance hose is attached to the Vortec air box and the other end connects to the motor. If you replace it yourself it should cost under $20.00 for the part and a little of your time.

Also, if that metal flap fell into the tank oh brother big job ahead of you or the repair shop. :eek:
 

Bhaasie

Member
Mar 15, 2012
9
I have a 2006 so no advance tube on resonator. Not sure what year they dropped em.

Keep the ideas coming thought. I'm open any suggestions.:wootwoot:
 

Forum Statistics

Threads
23,429
Posts
639,197
Members
18,647
Latest member
Lortigemt

Members Online