SOLVED! reoccuring low power / limp mode

[Ilikemy3s]

I figured I could not be the only to have had this experience, so figured to look here. Could not find another case. So here goes ..

Bit of a preface .. 05, SWB TB LT. 4.2 L6. Bought 6 years ago with approx. 85K miles. now has 233K. Have kept on on all maintainence.

A few months back when tropical storm Ada his the east coast, I was driving home from work and hit a hell of some puddles. Soon after, CEL and low power lights came on. I limped into a parking lot, hit the ON-Star Button for them to run a diag on the codes. They came back it. P2135, P2101, C0040, C0035, C0055. Mort of these reference traction control which I don't have. I figured something got wet. I let it sit and dry from engine bay heat. Started it up and only CEL came home. But it ran fine the rest of way home. Next morning I cleared the codes and the issue never came back.

Until.

This weekend, wife and I went to visit friends near Gettysburg PA. About a 3+ plus hour ride from home. Filled up on gas before trip. TB ran fine the entire trip. No hiccups, nothing unusual. We get there, park and enjoy the long weekend. TB was parked on a slight downward incline towards the passenger side during some steady rain two night in a row. Wife and I go to leave yesterday and it started fine. We leave and within 10 miles the CEL and LPL come on and it goes into limp mode. I pull it over and figure something got wet. Let it sit a bit and start it up .. starts fine. Start driving. I hear no unusual sounds from engine or trans and it is running as normal. but after about 5, same thing. But now i noticed it seems to stumble just before the lights come on and shortly after it stalls. Again, let it sit, start it .. drive a bit .. same thing.

By now I have pulled into a Sheetz gas/store and call AAA for a tow. The friend we stayed at came and picked us up and got us home. The truck got towed the 100+ miles and it front of my house. It started fine yet again as it was driving off the flat bed.

Any thoughts on how to start with this would be appriciated.

 

[Mooseman]

Try unplugging the fan. It's a known source of issues with the throttle system when it shorts out. If that doesn't fix it, you'll need an advanced scanner capable of showing live data between the pedal and throttle sensors to see which one is giving issues. Could be the pedal or the throttle body.

Failing not having a scanner, I would be inclined to suspect the throttle body because of the P2101 as this says that the throttle motor is not functioning properly. The P2135 would then say the pedal and the throttle sensor don't match because of the failing throttle actuator motor.

Have you tried cleaning it? It could be so gummed up it's not working properly. You also have to disconnect the battery while cleaning it (30 min.) to reset the PCM. Another possible course of action is to replace it with another one from a junker, which should be cheap enough if you have a PnP yard nearby.

 

[mrrsm]

...and here are a few more things that can cause the PCM to default a moving GMT360 to drop into “Limp Mode” and meet the overarching programming objective of Occupant Safety:

(1) A Bad Solenoid “B” inside the 4L60E Transmission.

(2) Changing the Tires to NON-OEM Height and Inflation Dimensions w/o PCM re-calibration.

(3) Failing or DIRTY Mass Air Flow Sensor AND... A Dirty Air Filter.

(4) Shorts in the MAF & IAT Wiring due to Cuts in the Wiring or Harness or Damage from an undiscovered Rodent Infestation.

Check GMTN FAQs for any related TSBs and SIs that might pinpoint the right repair procedures on some of these issues.

 

[Ilikemy3s]

Update : Air filter was dirty. DId not think it was that bad as I have not been driving much since last changed due to pandemic. The throttle plate, while was no were near as bad as last time I cleaned it at the 200K tuneup, I still took it off to clean. Reconnected the battery and took it for a drive, felt and drove normal. But .. about 20 mins into the drive, same issue but now only the P2135 is stored. Will still work on it.

 

[gmcman]

I wonder if the transmission wire harness had some water intrusion?

Would that cause these issues?

 

[Mooseman]

Did you try disconnecting the fan?

 

[mrrsm]

THIS Video about "A Trailblazer From HELL: Intermittent Reduced Power" shows what happens when you follow @Mooseman's suggestion (...but avoid allowing the Engine to overheat):

 

[Ilikemy3s]

will try disconnecting the fan when i get off work

 

[Ilikemy3s]

Update : Just to play it safe, I disconnected the battery for 30+ minutes . Reconnected it and then did a Throttle Body relearn since I forgot to do it after i cleaned it and reinstalled it just to be sure. Took it for a ride and same thing. At least I was in my housing development Limped home. Clear the codes and disconnected the fan circuit Took it for another ride so I could monitor various engine stats. No CEL and no loss of power And I took it for a longer ride. WHen i got home i did scan for codes and the only one I saw now was P0526 .. Fan speed sensor. But the CEL did not come on. Guess I am replacing the fan clutch now .. unless there is another trick to try ?

 

[Mooseman]

Nope. That's all she wrote. Try it a little longer with the fan disconnected (keeping an eye on the temps) to be really sure that is it.

One word on the fan clutches. ACDelco/Mahle/Behr are the best and run as designed. The Hayden is adequate and will work OK in normal circumstances (no heavy towing or extremely hot temperatures) as it will not run quite as well as the Behr.

EV Fan Clutch Recommendations for proper operation

Unfortunately I don't see the Behr available on RA anymore however did find one on eBay. The ACDelco is way overpriced.

N1067001 Cooling Fan Clutch Behr | eBay

Find many great new & used options and get the best deals for N1067001 Cooling Fan Clutch Behr at the best online prices at eBay! Free shipping for many products!

www.ebay.com

 

[59840Surfer]

1. Don't disconnect the battery every time you experience a problem. The HVAC system servo motors - mostly the plastic gears - are old and brittle and damaging them can be expensive and tedious to DIY.
2. Pull the various components fuses instead to do whatever you think it might accomplish - usually very little ... but it shouldn't hurt.
3. Always use a KAM Tool if you actually need to remove the battery.

Sidebar . .. our throttle bodies must be the filthiest ones in all of automotive history. Why should the first instructions be to "clean the throttle body" whenever a hiccup occurs?

Actually ... only clean air should EVER get to pass over, through, around or on it ... EVER!

But the mysterious PCV system* is usually the real problem. Clean it regularly and you should keep the brown slime attack on it from happening.
{* some people deny the existence of a PCV system on the Atlas engine. Unlike a good cheap steak, it exists.}
Brown-chocolate slime is not normal nor natural.

 

[Mooseman]

1. Don't disconnect the battery every time you experience a problem. The HVAC system servo motors - mostly the plastic gears - are old and brittle and damaging them can be expensive and tedious to DIY.

Although that is true, if they are weak, they will eventually fail so you'd just be delaying the inevitable. The actuators themselves are not that expensive and is doable by even the most novice DIYer. Only exception is the passenger side blend door which may require some surgery on a dash brace to access it.

2. Pull the various components fuses instead to do whatever you think it might accomplish - usually very little ... but it shouldn't hurt.

That is very poor advice. There are a few systems that do benefit from a reset, including the HVAC system and the PCM when the throttle is cleaned.

Sidebar . .. our throttle bodies must be the filthiest ones in all of automotive history. Why should the first instructions be to "clean the throttle body" whenever a hiccup occurs?

Actually ... only clean air should EVER get to pass over, through, around or on it ... EVER!

But the mysterious PCV system* is usually the real problem. Clean it regularly and you should keep the brown slime attack on it from happening.
{* some people deny the existence of a PCV system on the Atlas engine. Unlike a good cheap steak, it exists.}
Brown-chocolate slime is not normal nor natural.

Well, that's what we have so we deal with it. Poorly designed? sure but it's well documented and the knowledge is available to take care of it. I've seen throttle bodies that supposedly have only "clean air" going over them and they also get filthy. In fact, the procedure on ours is much easier than on LS V8 engines where you need an expensive scanner or Tech 2 to do a relearn. All we need to do is disconnect the battery or pull the fuses for 30 minutes to reset it.

 

[mrrsm]

...and not to put too fine a point on this issue... But...

The 'Mathematics of Combustion' provide enough information on their own merit to bear out the fact that ingesting "Clean Air" in any real sense becomes well nigh impossible. Look at the Numbers:

Using an 'Elderly Trailblazer or Envoy' as an Example Vehicle (4.2L)

240,000 Miles Traveled @ 18.5 Average MPG =
Burns 12,973 Gallons of Gasoline X
Using Air at a Ratio of 15:1 =
194, 595 Gallons of Air:



The real likelihood of having a substantial amount of Dirt and Dust Particles getting past any Filtration and winding up inside of the Engine makes it highly dubious that the Basic Engineering of ALL Throttle Bodies makes any difference in the absence of Proper Maintenance.

 

[Ilikemy3s]

Solved : Turns out the new Throttle I put on was indeed defective out of the box. The Fan Clutch I had put on when I got the TB about 6 years ago was innocent and indeed working fine. Also replaced the multi wire connector that connects to the throttle body for good measure. as it was showing signs of age. TB has been on the road back and forth to work on the 80 mile round trips with no issues.

 

[mrrsm]

A "Good Detective" Beats a "Bad Defective"... Every Time...

Sherlock Holmes (Automotive Consultations) :>)

 

[808]

A "Good Detective" Beats a "Bad Defective"... Every Time...

Sherlock Holmes (Automotive Consultations) :>)

gahahahahaha

 

[59840Surfer]

Although that is true, if they are weak, they will eventually fail so you'd just be delaying the inevitable. The actuators themselves are not that expensive and is doable by even the most novice DIYer. Only exception is the passenger side blend door which may require some surgery on a dash brace to access it.

You missed sumpthin' here .... the reset pushes the gears to MAX Travel to recalibrate --- and in normal operation --- once the physical limits of the travel are established .... the gears will not have to go that far again to satisfy swinging the doors to accomplish their designed-in and "found-physical limit" travel.

IOW --- once they find where they should not go, that is written into memory and the actuators won't push that far again --- UNTIL SOMEONE DISCONNECTS THE BATTERY or pulls the wrong fuse(s).

"Delaying the inevitable" is not really, truly correct 'cause if one does not disconnect the battery to purge the demons and malware from the system, then these modules won't have to perform this singularly destructive test until someone screws up.

 

[Mooseman]

GM didn't design a system that will self destruct in a normal self calibration operation. Everything ages including 20 year old plastic gears in actuators. Even if you can extend their life a little by just avoiding the reset, wouldn't be better to know that, on your terms, the possibility is there that it could break when you do the reset as opposed to an unknown time during intense cold and blizzard where you can't see out your windshield because it decided to fail regardless of the reset status. I've done MANY HVAC recalibrations and haven't suffered a failed actuator but have had some that just failed out of the blue on their own.

It will happen, just a matter of time.

 

[TJBaker57]

The only actuator I fear is the recirculation one buried deep in the dash. The three on the drivers side are childs play to replace. The passenger side blend I haven't had to do but doesn't seem to be that bad if I can get over my aversion to cutting things. But that recirculation actuator I do not care to think about.

 

[Mooseman]

The recirc I haven't heard of failing much. I don't think it does a recalibration since it only does open and close, no in-between, so it always travels to both ends.