2004 Tahoe Z71 5.3L Reduced Engine Power Issue

[KarenZ71]

Hello All,
Wanting to see if anyone might can help with some solid advice. Within the past month Tahoe had Reduced engine power all of a sudden with cruise set going 70 mph, check engine light. Got off the road, turned it off looked around the engine for anything abnormal and saw nothing. Started it back up and got it home. Drove fine for about 2 weeks and then had a crank no start. Before the tow truck arrived it started and got it back home. About a week or 2 later it had another Reduced engine power. Turned it back off, waited a min and it started back up again. The only stored codes I believe are:

-P0161
( Heated Oxygen Sensor (Ho2S) Heater
Performance Bank 2 Sensor 2 )

*U1000 & B0790 where on the same screen*
-U1000
( Class 2 Data Link Malfunction )
-B0790
( Transfer Case Neutral Indicator
Circuit Malfunction )

I do not know how to use the scan tool I had access to but if I did I'm sure I could have looked into things more.

As soon as I started having these issues I started cleaning all the grounds. Block grounds, Bat term ground, Bumper ground, driver side, etc I believe I got them all. I thought of inspecting the PCM but I'm not sure if I want to open a can of worms with the re-learn process if it's needed after unplugging. Is there a re- learn process needed after unplugging?

ABS is out but it's been a couple years now with out these issues. I've done spark plugs, wires, cleaned throttle body. May have a coil pack or 2 going out but not sure if that would cause these issues. Any advice is greatly appreciated, Thank you

 

[mikez71]

Often a bad accelerator pedal or throttle position sensor will cause REP mode..
The throttle actuator control (TAC module) connects to both TPS and Accelerator pedal, so if U1000 was due to that, that might cause REP..

Do you have ABS codes, since you said it's been out a couple years?
(possible the U1000 is related to abs module?)

I don't know anything about B0790..

If it happens again, keep checking codes, sometimes another one pops up later..

 

[Fless]

There is no relearn after disconnecting and reconnecting the PCM. You may want to carefully remove those two connectors and inspect them for corrosion or water migration. The gaskets can be replaced easily enough if any of that is noticed.

A crank-no start can be caused by many things (and I'm sure other members will add to this): bad crank sensor, bad ignition switch, lack of spark, fuel, or injector pulse, etc.

Another thing to inspect is the wiring from/to the throttle body; you have a drive-by-wire (electronic) throttle, so no physical cable. The wires near the throttle body can be compromised (broken) under the insulation; not easily seen but feeling them might indicate an issue. I would think there would be some Pxxx codes but stranger things have happened. As @mikez71 indicated the TAC module near the brake booster could also be in play.

If any of the codes have freeze frame data, that might show the anomalies or what triggered the code.

 

[Marky Dissod]

Everything already said ... also check ground straps for erosion / damage / wear, and grounding points for less-than-solid connections.
Although you should originally assume that each code is its own issue with its own solution,
can't hurt to clean / polish / re-cinch grounding points on a vehicle old enough to vote.

 

[KarenZ71]

Thank you all for the information. @mikez71 @Fless @Marky Things have been running fine even through the winter that I just went with the attitude that if it ain't broke don't fix it. Seems like everything is starting to show face. Ive been thinking of replacing parts so all this information points to great places to start.

@mikez71 Yes there is an active ABS and brake code. When that happened my brake module EBCM almost caught fire I believe. It had soot all around it. It's inches away from the fuel filter. It blew the 20 amp fuse as well. So kind of just let it be. I did send the board off to get repaired and purchased a used module. Braking the break lines loose from it have been the main reasons I haven't replaced it. But now I think it's time.

@Fless Thank you for the info. When cleaning the PCM if needed would you recommend using isopropyl alcohol a basic tooth brush perhaps and some wd40 on the pins before reconnecting?

@Marky Dissod Thank you as well. I did find my block ground strap is cut about an 1/4 of the way through so I will be replacing that. Mist definitely I'll take another look at the grounds. Thanks also for the great tip, treating each code separately definitely seems the best way to go. And without a doubt they are old enough to vote Hahaha! Built solid!

 

[Fless]

@Fless Thank you for the info. When cleaning the PCM if needed would you recommend using isopropyl alcohol a basic tooth brush perhaps and some wd40 on the pins before reconnecting?

I would say to use DeOxit or something similar (see below), and a soft toothbrush if needed. Then dry with compressed air before reconnecting. Read the instructions for whatever you use.

DeoxIT D-Series page with shop - CAIG

DeoxIT® D-Series contact cleaner dissolves oxides and sulfides that form on metal surfaces. This restores the contact’s integrity and leaves a thin microscopic layer that protects the metal. Special additives improve conductivity and prevent dissolved oxides from re-attaching, keeping them in...

caig.com

WD-40 Specialist Contact Cleaner Spray (not regular WD-40)

CRC 05103 QD Electronic Cleaner

 

[KarenZ71]

I would say to use DeOxit or something similar (see below), and a soft toothbrush if needed. Then dry with compressed air before reconnecting. Read the instructions for whatever you use.

DeoxIT D-Series page with shop - CAIG

DeoxIT® D-Series contact cleaner dissolves oxides and sulfides that form on metal surfaces. This restores the contact’s integrity and leaves a thin microscopic layer that protects the metal. Special additives improve conductivity and prevent dissolved oxides from re-attaching, keeping them in...

caig.com

WD-40 Specialist Contact Cleaner Spray (not regular WD-40)

CRC 05103 QD Electronic Cleaner

Ok, Looks like some great stuff. They have all different sizes and applications. Thank you

 

[RET423]

If your ABS light has been on it's possible that whatever caused it to come on (cold solder joints in the brain, bad wheel speed sensor,...) was not something that effects drivability; but over time you have lost functionality of ABS components that will effect drivability

For instance the wheel speed sensors are used for monitoring speed as well as tire slippage for the ABS system, if you lose one the light comes on but if you lose the rest over time the PCM loses the speed input when the final sensor quits; if it's failing intermittently like they often do it will drive fine whenever that last dying sensor is awake and derate when it drops out

They do strange things when the trans VSS doesn't get wheel speed data or vica-versa

I would make sure you don't have failed wheel speed sensors even if that's not the only thing causing your ABS light to be on, if the wheel speed sensors get fixed it likely will restore drivability even if your ABS brain needs a solder reflow to work again

 

[Electrickian]

Have you checked the wiring and connectors for Park/neutral safety switch module on the trans?