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Discussion Starter #1
1994 Deville with 4.9 L and electronic limited slip drivetrain, 155K miles

The vehicle runs and drives perfectly however, occasionally after a long hill or sudden acceleration we get the PO39 code (Torque Converter Clutch). It rarely happens in town and sometimes when on the highway.


It made sense at first since the car is old, but when I checked in the shop manual about the RPM difference needed to throw the code I was surprised it was around 400 rpm. Im pretty sure the slippage if any is below this number, but could be wrong.

One more piece of info. I think this started just after doing a tranny fluid and filter change about 20 k miles ago. I put in some valvoline tranny fluid, it was labeled as special for older transmissions with additives for conditioning seals etc. Im not too fond of snake oil treatments, but figured it wouldnt hurt. Now we think that there might be something about the fluid that might cause some slippage. Again, if there is any slippage it is minimal as the car accelerates like a rocket and pulls up mountain grades nicely.

I am going to change the fluid and filter again, its been about 20K miles since. Questions are:

!. Should we be worried about this code? What else could it be besides a slipping clutch?
2. What kind of Tranny fluid should we use?
 

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White Diamond '03 DHS (with DTS floor shift)
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Use what the owners manual calls for. I believe it is Dexron III.

Could be a TCC solenoid. What exactly is the code?
 

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Discussion Starter #3
The code is PO39. Can this solenoid be replaced without dropping the tranny?
 

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I had a very similar problem with my 1994 Concours last fall. I started a thread to get ideas. Ranger and CaddyDaddy as well as my friend Zorb750 were a big help. Long story short, I changed the fluid to Mobil One Synthetic and installed a new filter. Still had the codes. It turns out that a EPROM chip needs to be upgraded. I ordered one from gmpartsdirect.com. Please read the thread I posted on this issue.

http://www.cadillacforums.com/forums/cadillac-deville-1985-2005-including-1985/86779-obd-i-p039.html
 

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Discussion Starter #5
Hey, thanks for this additional information. From what I understand, this chip TSB is for the Northstar engine. We are running the 4.9L.

Since our car runs perfectly, I think we will just change the fluid and filter and live with the occasional error message. We might sell this car and if so it would be nice to not to have to explain any service engine lights (especially transmission related ones).

I read the shop manual, and the procedure for diagnosing this error code looks very complicated. I suspect it would cost hundreds just to have a dealer determine what is causing the error. Does anyone have any information that would confirm this?

PS Sorry to hear about the deer accident, I hope you were able to get the fender repaired without too much expense.
 

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Oh yeah, that happened in October, it was fixed, insurance covered it. I recently heard of a suggestion from a GM engineer who stated that the P039 code was common on the 1994's due to very narrow threshold times for torque converter lock up. He said adding no more than a half-quart of Type-F transmission fuild will fix the problem without adversly effecting shifting. Overtime the clutch in the converter can get a glazing on the surface allowing for light slippage therefore activating the code. I am told the Type-F will correct this. I have not added this, but it might be worth trying. Just don't exceed a half quart. I would start at 1/4 quart and make sure to remove from the regular fluid whatever you put in.
 

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Its good to hear that this is a common and probably not a sign of major tranny failure. I think we will replace the tranny fluid and filter and put the last half quart of type F. I dont see that can hurt anything and maybe will do the trick. I can floor it and race from stop to cruising speed without triggering it. The code is usually triggered when going up a long grade and particularly when we go wide open throttle up a grade. We dont notice any slippage, but who knows for sure what the slippage is. According to the manual, at these speeds the code shouldnt trip unless there is a 400 rpm difference. I think I could feel this, so it sounds reasonable that it trips the code early like the gm engineer claims.
 

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My understanding is the first program only allowed one second for clutch activation. The upgraded PROM chip increases this threshold to, I think, two seconds which is what the later program used anyways. I would be curious if the half quart of Type-F solves this problem. In my situation the only time I had the code was in stop and go traffic for over 10-15+ miles and it was not all the time. After I swapped the chip (and had the stupid deer damage fixed from test drive night) the code did not come back.
 

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Discussion Starter #9 (Edited)
Hey JCM1, it looks like I will need to try the upgraded EPROM chip. Im not sure where to find it at GMparts direct. I also have no idea where this chip is on my car or how to replace. I do a lot of mechanical work on our vehicles and in fact rebuilt the top end of the engine on this car, so I know my way around the 4.9. You mention in your thread that the TSB is for the 94 concours. Do you think that it has the same tranny as our 94 Deville? Ours is the model just below the concours.

Since I last posted, I put new filter and fluid in the tranny. Added about 1/3 quart of type F. Then I drove around like a maniac trying to get the P039 code to trip. It never happened so I figured it was fine. I was literally burning rubber and doing fast highway wot's...no code. Now a week later I gently leave a parking lot and get up to speed of about 30 mph and the service engine light comes on and P039 is current. The type F probably takes a while to do anything? Maybe the tranny is slipping a bit? I cant tell and its definitely not showing serious problems.

So I figure the $40 chip is the next step before tearing into anything. Any help/suggestions are much appreciated.

After doing some searching, the 4.6 and the 4.9 engines used different transmission number so maybe the TSB is only for the 4.6?

This is really frustrating. We want to sell the vehicle, it is running great and drives great, but this code is not helping matters!
 

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My 93 DeVille gets the P039 when going over rough roads. First time I took in into the shop, I told them I had a P039 code. I told them I thought that may be a Torque Converter Clutch issue. Shop Advisor said they would take a look. Came back that night after work, Shop advisor said I had a P039 code which is a Torque Converter Clutch issue, if I wanted the mechanic to take a look, it is an additional charge. This cost me $100.00. I just looked at the advisor and said, I knew that already, I needed to know if there was anything wrong with the Torque Converter, I already knew what the code said. I paid and left.

As for selling your car, it may not be 100% honest, but, clear the codes before you sell. If there is nothing wrong with the car, it is running at 100%, you are not total in the wrong giving a clean slate on the error codes.
 

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Discussion Starter #11
I spoke with my parents (the original owners) and they said it has been throwing the p039 code since it was nearly new. It hasnt thrown the code now for a few weeks of driving. We decided to keep the car so it really doesnt bother us anymore. Since the car drives like new, we find no reason to spend any dollars or time on this issue. Maybe the type F additive is working and it just needs some time to do its job. We never could determine if a chip upgrade is available for the 94 Deville with 4.9L engine. The previous posts refer to the 4.6L setup.
 

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I have the same problem on my 94 DEV. the engine light has been on for many years and all I got from other discussion boards was its going to cost a bundle to get fixed. Is there a way to get light to go off? The code is P039 History and no other codes. Car runs great but light comes on after 10-15 mi.drive and stays on.
 

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You can clear the DTC and the light will go out, but once the fault is detected again, the light will return. The only way to extinguish it permanently is to repair the fault.
 

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Well I have searched the sticky archives and can,t find it.
how about explaining it for me on a 94 deville 4.9 engine.
thanks in advance.
 

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White Diamond '03 DHS (with DTS floor shift)
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Simultaneously press and hold the OFF & WARMER buttons. The DIC will light up and then display the DTC's. After that use the HIGH FAN button to answer YES to the prompts and LOW FAN to answer NO. Answer no till you see CLEAR CODES?
 

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Discussion Starter #18
I think you can also clear the codes simply by removing the neg. battery cable for a few minutes. However, this wont do anything for your problem. The code will come right back. Its annoying for sure, but there isnt much you can do about it. Maybe if you could find the correct wire that sends the error signal, you could rig up a relay to fool the system, but I doubt this would be worth the time. We did something similar for the service ride control error and it worked great. I was really hoping that there would be a simple fix like the chip upgrade, but we have basically given up. The code is still occuring about every 2nd or 3rd time we drive it, we just ignore it. If the tranny ever shows signs of slippage, then we might think about doing something further.
 

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Well I sure agree with you there. I have had that damn light on for over7 years and 80,000 miles. the car runs great. It was off to-day for 42 mi. then I went up a grade hiway and all of a sudden on it came.
Ranger thanks for showing me the way.
 
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