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Urgent - My '09 GT is currently in the shop of my trusted mechanic to replace the Transmission Control Module (TCM). This as a result of in-depth diagnosis and trouble codes U0073, PO700, P2544, U0101 amongst others relating to Control Module Communications BUS "A" Off. He just called me once he pulled the transmission pan and fluid and noted to my shocking surprise that he found coolant mixed in with the transmission fluid. This car has regular maintenance, holds 151,000 Km. and had the transmission fluid and filter changed at 100,000 km.
Can anyone suggest to me from experience what else has malfunctioned to produce the condition of engine coolant mixed in the transmission fluid pan ?
 

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Trans cooler in the radiator failed.
 
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I thought I was the only one this happened to but I’m not too active on here anymore. I didn’t regularly maintain mine at the time and this was before modding. I ended up having to buy a new transmission because I let it go for too long. I think it’s apples to oranges here but I figured I’d mention I had the same problem. I hope yours isn’t as big of a problem as mine was. Good luck man!


09 G8GT yank3600stall, custom cam, Pat G tune, kooks LT,rotofab, 3.45 rear diff., no cats, ported heads~436/410
 

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Agreed. Rather surprised it doesn't happen more often.
 

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Agreed. Rather surprised it doesn't happen more often.
What do you mean by that? Is this a common problem and what are the signs of a problem and maintenance requirements?

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Am in agreement with the sentiments of JCMG8. The transmission "cooler" on many vehicles utilizes the cooling capacity of the radiator by circulating the fluid through a separate compartment i.e. cooler attached to the radiator. Considered how company bean counters cut corners daily in order to maximize profit, production rates, and streamline the manufacturing process am the least bit surprised when one fails. It only takes a single breach in the compartment and now the transmission and radiator fluid are mixing. It doesn't take long for the cross contamination to adversely impact one or both vehicle components. To the best of my knowledge, it's not too common or at least not frequently mentioned on the forum. Signs of a problem are discovering transmission fluid in the coolant or vice versa. Routinely checking the condition of the fluid helps, but it's not a maintenance issue but rather a design flaw. In my extremely humble opinion, any type of cooler whether it be oil, transmission, power steering, brake, etc. should be standalone.
 

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I have a Nissan truck where a weld In the radiators corrodes and caused leaking between the radiators and the transmissions for a number of model years. If not caught right away when the leak begins, it will wipe out the friction disks and electrical controls in the transmission. They were able to identify the radiators affected. I had one and preemptively replaced it with one from a different manufacturer.

I only found out about the failing radiators from the truck forums.
 

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Am in agreement with the sentiments of JCMG8. The transmission "cooler" on many vehicles utilizes the cooling capacity of the radiator by circulating the fluid through a separate compartment i.e. cooler attached to the radiator. Considered how company bean counters cut corners daily in order to maximize profit, production rates, and streamline the manufacturing process am the least bit surprised when one fails. It only takes a single breach in the compartment and now the transmission and radiator fluid are mixing. It doesn't take long for the cross contamination to adversely impact one or both vehicle components. To the best of my knowledge, it's not too common or at least not frequently mentioned on the forum. Signs of a problem are discovering transmission fluid in the coolant or vice versa. Routinely checking the condition of the fluid helps, but it's not a maintenance issue but rather a design flaw. In my extremely humble opinion, any type of cooler whether it be oil, transmission, power steering, brake, etc. should be standalone.
Got it. Thank you.

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I have a Nissan truck where a weld In the radiators corrodes and caused leaking between the radiators and the transmissions for a number of model years. If not caught right away when the leak begins, it will wipe out the friction disks and electrical controls in the transmission. They were able to identify the radiators affected. I had one and preemptively replaced it with one from a different manufacturer.

I only found out about the failing radiators from the truck forums.
Thanks

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I had this problem about four years ago in one of my Base G8's. It was found when doing a normal transmission service. An OSC radiator was installed, and the cooling system and transmission were both flushed. New transmission fluid and filter, and waterless coolant were installed. No more problems have been had with the cooling system, and the transmission lasted another 30,000 miles before replacement.
 
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