Hello all, I’ve been sneaking around on your site for years and have benefitted greatly while owning 3 first gen RL’s. When Covid hit, I picked up a 2021 sport through Copart that ended up needing an engine swap after their fork truck kissed the bottom of the crank through the oil pan. I did a complete engine/trans swap swap with no problems, but ended up having a P0841 code in my 9 speed that I couldn’t figure out after a 10 mile test drive. I then swapped in a second 9 speed transmission only to be stuck with the same code. I’m trying a new to me TCM, but can’t get the truck to read the new module. Does anyone know if the TCM is coded to the PCM or if it should be plug and play?
2021 ZF 9 speed woes
crownryal
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Hello all, I’ve been sneaking around on your site for years and have benefitted greatly while owning 3 first gen RL’s. When Covid hit, I picked up a 2021 sport through Copart that ended up needing an engine swap after their fork truck kissed the bottom of the crank through the oil pan. I did a complete engine/trans swap swap with no problems, but ended up having a P0841 code in my 9 speed that I couldn’t figure out after a 10 mile test drive. I then swapped in a second 9 speed transmission only to be stuck with the same code. I’m trying a new to me TCM, but can’t get the truck to read the new module. Does anyone know if the TCM is coded to the PCM or if it should be plug and play?
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On the 9speeds I'd bet it needs a scan tool of some type to calibrate the new to it PCM to the transmission. Rarely anymore are things setup perfectly enough that you don't have to program them. Also, I'm sure there's some type of communication with the main MCU that does serial numbers and whatever else is going on. Your best bet would be to find an aftermarket shop with some good scan tools for Honda and let them review what is going on before more swapping.
Thank you kindly. I actually called my local Honda shop, and much to my surprise, they said they’d be glad to program a used TCM for me. The only issue is this super smart transmission that only lives in park and neutral when there is a fault present. I have a relatively high end scantool (I usually work on Audi/VW) that does a good job at reading the code and it does show a serial number for the module like you brought up. I guess I’ll have to rollback the old devil to the shop and let them take a peek at it. I was hoping someone knew a hack to get the thing mobile. The funnier story was watching me get it off the delivery truck with a hole in the oil pan and no neutral lock tool…a 4k mile 3.5 never sounded so bad!
Much appreciated. I may just leave the original TCM in there and see if they can update it. If it ends up being a wash, I’ll have them swap in the new used one, update it, and then do the hydraulic pressure calibration. I wonder if that calibration is my main issue…
Correct. I used the original TCM. It didn’t show any codes and operated properly until around 10 miles after doing the swap. I was facing uphill and had the truck in Park just to check for any codes on my scanner. When I put it back into Drive, it gave me the transmission warning and went into limp mode after making a rather loud clank while trying to go into gear. After I pulled it home in neutral, I pulled the fluid and found a bunch of material suspended….thus the transmission swap. I dropped the transmission and put in a second unit. It fired up and I was able to move it around the driveway. After about five minutes of idling, I received the P0841 code. Once I saw that code, I ordered a used TCM in hopes of ruling out the module
I absolutely will. I’m betting that the parameters set in the TCM from the first 4k miles aren’t anywhere near what it’s showing now., especially since I ran non Honda fluid for those 10 fateful test drive miles (I know, I know…I’ve since learned my lesson)
I really appreciate you guys getting me some info. There’s not a lot out there for goofballs like me, getting into silly situations like this….the truck was supposed to be a “runs and drives” copart deal, but giant holes in the bottom end tend to make things not run.
I sure wish there was a way to zero out the TCM from home so I could avoid the whole rollback situation
I really appreciate you guys getting me some info. There’s not a lot out there for goofballs like me, getting into silly situations like this….the truck was supposed to be a “runs and drives” copart deal, but giant holes in the bottom end tend to make things not run.
I sure wish there was a way to zero out the TCM from home so I could avoid the whole rollback situation
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Know a Honda tech ? Get them to bring home a Honda tech tool to your garage !
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Turbo 400. The good old days. 
I’m a firm believer that any of these transmissions can be serviced and worked on. I’ve dealt with ZF equipment for years in the Audis, BMW’s and they can absolutely be worked on if you meet the right people….however; the tech end with the modules is what kills me. I pulled apart the first transmission that was in this truck originally and it’s mechanically no different than any of the other ZF models, just a little more compact. The valve body and solenoid pack is pretty much the industry standard at this point for an electronically controlled transmission
Honda recommends service on the ZF9.
She’s getting loaded up today and will likely sit in the back lot of the dealer for a month til they get to it. I’m hoping this is the fix. The internals of this model transmission are pretty robust, so I’m hopeful for a quick heal.
As far as servicing it goes, as long as you have a decent scanner that’ll monitor fluid temp, it’s as easy as pulling the plug, draining, dumping in 3.5 quarts of liquid gold Honda 3.1, then checking the overflow once you hit target temp. A lot of new transmissions say they’re non serviceable…which makes it a lot easier for the dealers to sell you a brand new unit if your valve body or pump fails.
As far as servicing it goes, as long as you have a decent scanner that’ll monitor fluid temp, it’s as easy as pulling the plug, draining, dumping in 3.5 quarts of liquid gold Honda 3.1, then checking the overflow once you hit target temp. A lot of new transmissions say they’re non serviceable…which makes it a lot easier for the dealers to sell you a brand new unit if your valve body or pump fails.
Just a quick update. After a tow to and from my local a Honda dealer and 3.5 hours of diagnostics, my transmission was deemed “unserviceable”. I was able to get my spare TCM an education so that it’ll communicate with my PCM. In the end, the work order stated there were too many “what ifs” for them to be able to diagnose any issues and after clearing the P0841 code multiple times, it persisted. After speaking with the service manager, it’s my belief that Honda isn’t really a big fan of opening these transmissions to diagnose internal faults, even with the valve body that lies just beneath the front cover.
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No they are swap till you drop shops anymore. There's really no diagnosis at a dealership. You'd have to go to a real transmission repair shop for real repairing of them. Even then the 9 speed is still pretty new and you'd have to find a place that wants to tinker with it and try and understand the failure mode occurring. (meaning they learn and don't charge the hourly rate they normally would... like my buddy's place in Coroapolis.... he's like that. He just charges what should be charged and fixes them no matter the time spent.) (Was just down there this week for my annual Fluid film touchup. Did it on the lift while truck was inspected for PA inspection... passed again still original brakes at 67k)
I was pretty much figuring on them wanting to swap in another unit, so I’m okay with getting the spare TCM programmed just so I know it’s flashed with the latest coding. I know I’m working with a good unit. I’ve rebuilt quite a few transmissions, so I’m not terrified of learning about the 9 speed. I’m going to pull the valve body and replace it for another run at backyard diagnostics. The price they gave me for labor to replace the transmission was pretty spicy…around $3600 in just labor. I’m on the lookout for a low mileage ZF9 at this point as a backup plan
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