2020 Silverado with a transmission problem - P176B

[Dborch41]

Yeah I know, what are the odds? It's the usual 5.3/8L90E combination, the truck has already been to the dealer twice for a new torque converter then a bad shift solenoid. Fortunately those were all under warranty, but 6 years and 32K miles later...no such luck.

The issue is DTC P176B, which is a problem with the transmission speed sensor. I was a few miles from home when the code tripped, and it seemed to drive OK so my hopes were up it was noting serious. My scanner had another story. I called one of the more reputable transmission shops in town, and the second I mentioned the model and code the guy told me that would be dealer-only. Something about parts availability and other issues, or maybe they just didn't want to take a chance with such a notorious transmission. Can't say I blame him.

Now that it's coming out of my pocket I don't want to drive it anymore and risk further damage, not to mention that's probably not very safe. My question is if anyone else has had the same issue and what the outcome was, and if maybe I should shop around for another independent shop or bite the financial bullet at the dealership.

Any input is appreciated.

 

[SatinSilver]

@clinebarger can help here.

 

[GSCJR]

Poor @clinebarger.

 

[nascarnation]

This may be useful:

 

[clinebarger]

P176B is a Performance DTC....Meaning the TCM isn't detecting any voltage range errors on the intermediate sensor signal circuit but its seeing RPM in 1st/2nd gear or the incorrect RPM in 3rd/4th/5th/6th/7th/8th gears.

Does your scan tool read live transmission data? Even better if it can graph the data PID's?

P176B

Condition 1
Transmission Intermediate Speed Sensor = Greater than 60 RPM — Gear 1, 2
Condition 2
Transmission Intermediate Speed Sensor — Slip Detected = Greater than 60 RPM — Gear 3, 4, 5, 6, 7, 8

 

[robbobster]

FYI you can download the service manual for free here:
https://lemon-manuals.la/

…and not just for Chevy, there’s tons of manuals for most makes and models.

 

[Dborch41]

This may be useful:

I found that video during my research, unfortunately I don't have the equipment (or the knowledge to be perfectly honest) for that level of troubleshooting.

There was a time when I could, comprehension-wise, but not so much anymore. Long story...

 

[clinebarger]

I'm not scared of a 8L90 if you're in the DFW area.

 

[Dborch41]

P176B is a Performance DTC....Meaning the TCM isn't detecting any voltage range errors on the intermediate sensor signal circuit but its seeing RPM in 1st/2nd gear or the incorrect RPM in 3rd/4th/5th/6th/7th/8th gears.

Does your scan tool read live transmission data? Even better if it can graph the data PID's?

P176B

Condition 1
Transmission Intermediate Speed Sensor = Greater than 60 RPM — Gear 1, 2
Condition 2
Transmission Intermediate Speed Sensor — Slip Detected = Greater than 60 RPM — Gear 3, 4, 5, 6, 7, 8

Here's what I have.

Not exactly professional grade, but marginally better than your average parts store code reader. I actually got this unit because it was the only consumer-grade scanner that could access Nissan ABS systems (please excuse the literary redundancy). I had a Frontier with a stubbornly soft brake pedal that fought every attempt at conventional bleeding techniques, this made a difference.

It is bidirectional, but I never really investigated its capabilities beyond actuating Nissan ABS solenoids, which it did quite well. I only used it to read the codes on the Silverado, maybe I should do a deeper dive on what else it can do.

Thanks for the input.

 

[Dborch41]

I'm not scared of a 8L90 if you're in the DFW area.

A bit farther south actually, Corpus to be exact. Of course in Texas there's no such thing as "a bit".

I've had friends from New England come down to visit and couldn't wrap their heads around the idea of driving all day and still being in the same state.

I sincerely appreciate the consideration.

 

[robbobster]

I've had friends from New England come down to visit and couldn't wrap their heads around the idea of driving all day and still being in the same state.

Yeah this state is huge.

El Paso, TX is closer to the CA border than it is to my house near Dallas

 

[clinebarger]

Pepe Torres/Aus-Tex Transmission is way closer in Austin/Taylor, Texas

 

[Dborch41]

Pepe Torres/Aus-Tex Transmission is way closer in Austin/Taylor, Texas

I'm considering taking the plunge on paying to have the transmission "bulletproofed". I've called one local shop so far, they're going to get back to me with an estimate. I'll call some others as well, there are quite a few in town.

I know there are bigger cities not too far away with more options, but that would require paying to get the truck fixed locally then making the drive out of town for the upgrade. I'd rather avoid that if possible but I'll weigh all the options. Regardless, I don't have any faith in the transmission in it's stock form...not after three strikes.

 

[clinebarger]

Be careful, Many shops can build a 4L60 or 6L80 all day but don't know the 8 speed well enough to fix it right the first time or ever for that matter.

 

[Dborch41]

Be careful, Many shops can build a 4L60 or 6L80 all day but don't know the 8 speed well enough to fix it right the first time or ever for that matter.

That's probably why the first shop I called, also the highest-rated one, declined to even look at it. I might be limited to going to the dealer again, too bad this time it's going to be out of my pocket.

 

[clinebarger]

It's more than likely the speed sensor/internal transmission harness causing the current issue, But harness rub is an issue with T1 chassis trucks especially '19 & '20.

Good for them declining the work....Sensor Performance DTC's can get messy knowing how the system works...Not knowing usually ends with a parts cannon!

 

[Dborch41]

It's more than likely the speed sensor/internal transmission harness causing the current issue, But harness rub is an issue with T1 chassis trucks especially '19 & '20.

Good for them declining the work....Sensor Performance DTC's can get messy knowing how the system works...Not knowing usually ends with a parts cannon!

I watched a video on how to access the speed sensors, once they got to "now we'll remove the valve body" I tapped out.

When it comes to automatic transmissionmission valve bodies...here there be monsters.

 

[clinebarger]

Pulling the valve body is fairly straight forward on these compared to earlier designs like a 4L60 for example.....No gaskets to rip.....No check balls running down the driveway.
But if you don't feel comfortable messing with it....Don't!

 

[Dborch41]

Pulling the valve body is fairly straight forward on these compared to earlier designs like a 4L60 for example.....No gaskets to rip.....No check balls running down the driveway.
But if you don't feel comfortable messing with it....Don't!

I wouldn't mind it if I had a lift, but I'm too old to be tackling that flat on my back in the driveway.