2012 TAHOE HYBRID CODES P0AC4, U186A, U186B

[Tahoeman12]

I'm in possession of the truck and it's driving great and it's not gone into limp mode yet..... they did clear all the codes so hopefully that will make a difference. If the problem persists then I will try to find another shop that has the software to dig deeper into my issues. What I'll do next time is once it goes into limp mode instead of disconnecting the battery to get it to drive again, I'll leave it as is and have it towed to the shop. Thanks for all the information so far, really appreciate the feedback.

 

[j91z28d1]

I'm in possession of the truck and it's driving great and it's not gone into limp mode yet..... they did clear all the codes so hopefully that will make a difference. If the problem persists then I will try to find another shop that has the software to dig deeper into my issues. What I'll do next time is once it goes into limp mode instead of disconnecting the battery to get it to drive again, I'll leave it as is and have it towed to the shop. Thanks for all the information so far, really appreciate the feedback.

any luck?

 

[Prae71]

I'm in possession of the truck and it's driving great and it's not gone into limp mode yet..... they did clear all the codes so hopefully that will make a difference. If the problem persists then I will try to find another shop that has the software to dig deeper into my issues. What I'll do next time is once it goes into limp mode instead of disconnecting the battery to get it to drive again, I'll leave it as is and have it towed to the shop. Thanks for all the information so far, really appreciate the feedback.

I believe I had a similar issue with my Yukon. The wife had a small fender bender, she got hit in the rear driver tire, which knocked a communication wire out of place under the driver side passenger door. I fought this for a few weeks and then took it to the dealer which couldn't replicate the symptoms. As I left the dealership, all the lights popped on and went into limp mode. I took it to a different dealership who actually took the time to diagnose it. It was in their possession for 5 months. After warranties on 3 different modules and no luck fixing it. The technician opened the rear passenger door while looking at the modules and *BAM* everything triggered again. It wound up being 2 wires on the main can bus that were wore into about the size of my pinky nail. That fixed it and I've never had that issue again in the 6 years since. Not a fun time, but sounds like you need to chase wires and not worry about the modules quite yet.

 

[Tahoeman12]

I"m just now getting an update to post. When I went to pick up the Tahoe at the dealership and drove it home it went into limp mode again. I pulled the truck off to the side of the road, turned the engine off and started it backup and limp mode was gone but the check engine light was still on. I drove it back to the dealership and they said they would look at it again now that it went into limp mode. Well thesis with it for 5 weeks and pulled codes but told me they didn't really want to fix the truck and to come get it.

So these are the codes that they pulled after I brought it to them.U186A, U186B, U1888 AND P0AC4, C0242, C0750. In looking at the codes I'm thinking the trouble is the modules aren't able to talk to each other. I have my mechanic come by later this week and confirm the hybrid battery is still good and then to check the wiring to the TCM and surrounding areas and to drill down on the U1888, U186A and U186B,

Could it be as simple as the hybrid battery on it's last legs causing the codes?

 

[j91z28d1]

it is possible for the communication system to fault if the power goes so low the modules power drops off for a second. see that a lot in standard trucks when the 12v battery is very weak and guys keep trying to start it but it bearly turns over. you have to clear all the U codes after charging or replacing the battery.

does you truck buck badly when rolling away from say a stop sigh on battery and then when it starts the engine it bucks? that's a clear sign the hybrid battery is to weak to move the truck and crank the engine at the same time without power crash.


you can try by driving in m4 mode, it won't go into auto stop, so it the engine is always running producing power. so the hybrid battery isn't used as hard.

reduced power a lot of times is throttle body or throttle pedal issues too. maybe ask your mechanic to check the data from those?

 

[Tahoeman12]

it is possible for the communication system to fault if the power goes so low the modules power drops off for a second. see that a lot in standard trucks when the 12v battery is very weak and guys keep trying to start it but it bearly turns over. you have to clear all the U codes after charging or replacing the battery.

does you truck buck badly when rolling away from say a stop sigh on battery and then when it starts the engine it bucks? that's a clear sign the hybrid battery is to weak to move the truck and crank the engine at the same time without power crash.


you can try by driving in m4 mode, it won't go into auto stop, so it the engine is always running producing power. so the hybrid battery isn't used as hard.

reduced power a lot of times is throttle body or throttle pedal issues too. maybe ask your mechanic to check the data from those?

good morning and thank you for the response. I cleaned the throttle body already but I'll look at the throttle pedal too.

 

[Tahoeman12]

it is possible for the communication system to fault if the power goes so low the modules power drops off for a second. see that a lot in standard trucks when the 12v battery is very weak and guys keep trying to start it but it bearly turns over. you have to clear all the U codes after charging or replacing the battery.

does you truck buck badly when rolling away from say a stop sigh on battery and then when it starts the engine it bucks? that's a clear sign the hybrid battery is to weak to move the truck and crank the engine at the same time without power crash.


you can try by driving in m4 mode, it won't go into auto stop, so it the engine is always running producing power. so the hybrid battery isn't used as hard.

reduced power a lot of times is throttle body or throttle pedal issues too. maybe ask your mechanic to check the data from those?

How do I get it into M4 mode?

 

[j91z28d1]

m4 is just on the shifter. one notch before drive. move it down one you'll see m4 on the display and then you'll also see a toggle switch on the shift handle. that will move down to m3, m2 and m1. that is basically 1st gear, 2nd gear, 3rd or 4th.

it doesn't hold that one gear, it's just sets the top gear. like say you put it in m3. from a stop it will take off in 1st, shift 2nd and then 3ed. it won't shifter higher than the m number you're in.

it won't shift into over drive in m4. so highway speeds arw higher rpm, but around town its not bad, and it doesn't go into auto stop. to it helps to tell if auto stop is causing your issue

 

[Tahoeman12]

How do I get it into M4 mode?

never mind, I figured out what M4 mode is.

 

[Tahoeman12]

m4 is just on the shifter. one notch before drive. move it down one you'll see m4 on the display and then you'll also see a toggle switch on the shift handle. that will move down to m3, m2 and m1. that is basically 1st gear, 2nd gear, 3rd or 4th.

it doesn't hold that one gear, it's just sets the top gear. like say you put it in m3. from a stop it will take off in 1st, shift 2nd and then 3ed. it won't shifter higher than the m number you're in.

it won't shift into over drive in m4. so highway speeds arw higher rpm, but around town its not bad, and it doesn't go into auto stop. to it helps to tell if auto stop is causing your issue

I put it into M4 this morning and did a 30 minute drive and the truck went into reduced engine power mode again. Lost all gears and pulled to the curb. Turned engine off and back on again and was able to return home no problem. Same codes same issues. UGH.

 

[j91z28d1]

well it was a long shot, but should rule out the hybrid battery cells being weak enough to cause issues.

there's a tsb about wiring, but I don't know if it helps you. I'll add it thou.


quick thought. are your battery cables tight on the 12v? being quick release, I seem to remember someone posting forever ago about needed to shim the battery posts, so the terminals are tight. you shouldn't really he able to move them by hand without a lot of force. I only thought about it because of a thread of a non hybrid truck doing weird stuff over bad battery cables. these do weird things is the 12v side isn't solid too.

 

[Tahoeman12]

well it was a long shot, but should rule out the hybrid battery cells being weak enough to cause issues.

there's a tsb about wiring, but I don't know if it helps you. I'll add it thou.


quick thought. are your battery cables tight on the 12v? being quick release, I seem to remember someone posting forever ago about needed to shim the battery posts, so the terminals are tight. you shouldn't really he able to move them by hand without a lot of force. I only thought about it because of a thread of a non hybrid truck doing weird stuff over bad battery cables. these do weird things is the 12v side isn't solid too.

I had my mechanic disconnect and reconnect the 16 wire connection to the transmission, checked all the grounds and yes the battery terminals are super tight. The hybrid battery checked out good at 313 volts. I ordered an OEM throttle pedal this morning.