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Check Engine Light/DIC "Engine Reduced Power"

K10Guy

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Shortly after putting the truck in cruise @ 60, I felt a little hard shift. DIC stated that the engine has reduced power, then the check engine came on. Also the RPM increased from 1500 to 3000rpm. Turned off the cruise and I was still getting high RPMs and check engine light. Pulled off the side of the road, turned off engine, then started the truck again. Even though the check engine light continued to stayed on, restarting the truck helped with the RPM issue. Plugged in my BlueDriver and it came up with the following codes:
P0700- Transmission Control System
P176B "Check Report for Description" ??
U0100- Lost Communication with ECM/PCM "A"
U0101- Lost Communication with TCM
The 2022 Trail Boss will be seeing the GM Service Tech Monday for the first time, with 899 miles on her. I'll post the findings/corrections after they look at her. Like to note that the myChevrolet apps stated everything is fine/no issues. Makes me question how great that app really is, other than having the ability to start the truck and lock/Unlock the doors.
 

tbuss5831

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Ok soo looking at the P176B would be why you felt a hard shift and RPM increase as this will cause the transmission to only allow gears 1-5 and R. Also the trans will always resort to full line pressure if their is a fault, thats the hard shift. Loss of comm codes get tricky, could be you just have a shit battery that dropped voltage for a split second and caused the network to glitch (seen this plenty of times). Could be you have a wire in the harness that just barely rubbed through and shorted on something metal, less common, but still I have seen it. Good news, its under warranty. Just thought I would post this so you had a little bit of information on what it could be.
DTC P176B
Intermediate Speed Sensor Circuit Performance
 
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K10Guy

K10Guy

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Ok soo looking at the P176B would be why you felt a hard shift and RPM increase as this will cause the transmission to only allow gears 1-5 and R. Also the trans will always resort to full line pressure if their is a fault, thats the hard shift. Loss of comm codes get tricky, could be you just have a shit battery that dropped voltage for a split second and caused the network to glitch (seen this plenty of times). Could be you have a wire in the harness that just barely rubbed through and shorted on something metal, less common, but still I have seen it. Good news, its under warranty. Just thought I would post this so you had a little bit of information on what it could be.
DTC P176B
Intermediate Speed Sensor Circuit Performance
Hopefully GM Service Tech can find the issue (bare wire/shortage, etc). Fell in love with this Chevy trim after debating on getting the TRX. Hate for it to be in the shop just after pushing 900miles but glad it happened under warranty. Contacted the dealership and within the hour, they replied by email and by a phone call. Very helpful squeezing me in for an appointment Monday (2 days after issue accurred) and a rental. It would be another week or so if I chose the dealership near my location.

Thanks again tbuss for the reply. I'll keep yall posted.
 

Tobi1kinobi

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I had something similar happen to me. I took it straight to the dealer and they ended up having to put whole new transmission in. It had less than 4000 miles on it when that happened. Hopefully they can fix yours without having to take that drastic of a measure.
 
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K10Guy

K10Guy

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I had something similar happen to me. I took it straight to the dealer and they ended up having to put whole new transmission in. It had less than 4000 miles on it when that happened. Hopefully they can fix yours without having to take that drastic of a measure.
Dang, that escalated quickly. Lol. Really, thank you for your input. Crazy thing is, I drove it 2hrs on interstate 70-80mph yesturday, and it didn't even "reduced engine power". I will note that the battery was way lower than normal and the check engine light stayed on. Plus, every now and then on the interstate, it would feel like it was going to drop power at any giving moment. Or maybe it was my mind playing tricks. I just wanted to get the truck at the dealership and not get stranded.
 

Tobi1kinobi

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I had something similar happen to me. I took it straight to the dealer and they ended up having to put whole new transmission in. It had less than 4000 miles on it when that happened. Hopefully they can fix yours without having to take that drastic of a measure
Dang, that escalated quickly. Lol. Really, thank you for your input. Crazy thing is, I drove it 2hrs on interstate 70-80mph yesturday, and it didn't even "reduced engine power". I will note that the battery was way lower than normal and the check engine light stayed on. Plus, every now and then on the interstate, it would feel like it was going to drop power at any giving moment. Or maybe it was my mind playing tricks. I just wanted to get the truck at the dealership and not get stranded.
I originally took it in for a noise that it is still making. Whenever I slow down to about 15 miles an hour there's a rattle coming from underneath. They tell me that's normal. I'm taking it to another dealer for a second opinion. They replaced something to do with the torque converter(don't remember what specifically). That didn't fix it. A week later is when I had the same issue you had. It was shifting really weird, and really hard. I had to limp it back to the dealer. Then they said they weren't going to chase the issue, so they replaced the transmission. I literally just picked it up today, and it is still making the same noise underneath that I originally took it in for.
 
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K10Guy

K10Guy

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Update: Just heard back from the dealership. Truck should be ready to be picked up either tomorrow or Wednesday. They stated that the issue was a bad Speed Sensor. Fingers crossed that the issue will be fixed.
 

Gibby

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Update: Just heard back from the dealership. Truck should be ready to be picked up either tomorrow or Wednesday. They stated that the issue was a bad Speed Sensor. Fingers crossed that the issue will be fixed.
Yeah thats what I was thinking when I seen the P0700 code. This is the code for a general Trans failure usually associated with the output shaft speed sensor internal to the Trans. Most of my experience with this has been a wire broke loose from the terminal at the Trans Connector. But I have seen where the sensor has failed as well. In some cases when that code sets the TCM will disable 4x4 shifting, wont allow the use of tow haul mode and as tbuss has already stated, will limit the shifting range.
 
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K10Guy

K10Guy

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Update #2: Sat Mar 12, 2022; Trail Boss hasn't returned home. Last time I saw her was Mon Feb 19, 2022. Made my first payment while driving a rental lol. Smh. Apparently the issue repeated itself even when Chevy Service Tech replaced the speed sensor. So, we are back at square one. However, this go around, they have assistance from GM TAC. On the plus side, saving a shit ton on gas money driving this rental. 😁
 

Bertsboss

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Hopefully will get issue resolved.
My truck is a 21 with less than 5,000 miles on it, at dealer for flashing engine light really rough running.
 

Gibby

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Hopefully will get issue resolved.
My truck is a 21 with less than 5,000 miles on it, at dealer for flashing engine light really rough running.
Flashing engine light is not good. get it to the dealer quick or you may end up replacing your catalytic converters.
 
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K10Guy

K10Guy

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Update #3: Day 37...I must say, having the rental more then the trailboss is pretty sick (old meaning fyi). GM engineer diagnosed the issue and stated it was in the harness. I requested more info on which harness needs replacement. As of last Friday, service department was waiting for part. Very anxious getting her back.
 
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K10Guy

K10Guy

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Update #4: Picked up the TB Apr 4th. Service Tech replaced the Pass-Through Harness and body control valve. Issues seemed to be resolved. Drove it back from the dealer (200 miles) and to Atlanta (80miles round trip). Everything was looking great. Drove it another 20 miles and issues re-appeared. Limping all the way to a closer dealership. 4 days in the shop and the service tech stated it was something in the transmission. They would have to run more tests to see if they can replace parts or worse case, replace the whole transmission. Back with the rental car. Lmao
 
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