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Hi All,

The torque converter on my Odyssey is acting up (CEL P0740) and I am in the process of troubleshooting the cause. There are quite a few gotchas so I'm making this post to help anyone else that finds themselves in the same position. That way my suffering will not have been in vain.
 

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The first step in the service manual is to perform a line pressure check. This appears to require a load of special Honda tools but can be performed with any oil pressure tester. Of course you have to find the test ports first and the manual is not much help. After a few hours digging through the top of the transmission I jacked up the van and found that the ports are easily accessible from underneath. I will take a photo the next time I an under the van.
 

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Minor note; oil pressure test kits seem to only be available with 100 psi and 400 psi gauges. 100 is too low for any of the pressures in this transmission and 400 is far higher than necessary. Given the narrow acceptable pressure range, too large of a gauge could make it difficult to determine whether the pressure is correct. 200 psi gauges are less than $10 so I bought one just in case. I will test both and update this post with the result.
 

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Finally the gauge has to actually be connected to the transmission. I figured at least one of the adapters that came with my kit would work but I was wrong. I bought another kit at harbor freight that included even more adapters but still none of them worked. Long story short; the test ports use an M8 x 1.25 thread. I have ordered the (hopefully) correct adapter and will report back when it arrives.
 

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Thanks. I appreciate your posts. I had same code once and I just drained and filled with valvoline maxlife atf. Not saying anything but that code has not returned. Wish you the best of luck. Please correct the code in title of thread from P0470 to P0740. Thanks
 

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Thanks. I appreciate your posts. I had same code once and I just drained and filled with valvoline maxlife atf. Not saying anything but that code has not returned. Wish you the best of luck. Please correct the code in title of thread from P0470 to P0740. Thanks
Good catch; fixed now.
 

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I wish you the best. Like many others, I switched from DW-1 to MaxLife (after switching from Z-1 to DW-1) on my '99 and along with a really good ATF cooler (TruCool 4544), frequent ATF changes, and gentle driving, finally got my AT to last a long time in my '99.

But it might help you to know that back in the days when these ATs were subject to extended warranty due to the lawsuit settlement, if you went into a dealership with a P0740 code, they would not crack open the service manual or test anything. They'd order a new (rebuilt) transmission and swap it in.

Perhaps they had procedures back at the Honda rebuild factory to diagnose, etc., but that code was assumed to be fatal.

And BTW, if you get the TCS light on as well, no need to worry about that - it's not a different problem. It's due to the AT / torque converter problem.

Good luck.
 

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Some fluid change history would help here
Fluid history is pretty sparse. It has been changed at least once but no more than twice.

I wish you the best. Like many others, I switched from DW-1 to MaxLife (after switching from Z-1 to DW-1) on my '99 and along with a really good ATF cooler (TruCool 4544), frequent ATF changes, and gentle driving, finally got my AT to last a long time in my '99.

But it might help you to know that back in the days when these ATs were subject to extended warranty due to the lawsuit settlement, if you went into a dealership with a P0740 code, they would not crack open the service manual or test anything. They'd order a new (rebuilt) transmission and swap it in.
Good call on the MaxLife. If the engine is fixable (blown head gasket) I will definitely switch. I believe it is currently filled with DW1 since the last fluid change would have been after Z1 was discontinued. Is MaxLife compatible with DW1?

As for P0740 being a fatal code back in the day, I don't doubt that Honda had the data to back that up. However these days I'd bet that that's no longer the case. Likely P0740 is only a fatal code if the transmission was fairly new. I also thought honda fixed the transmission issues for the 2004 model year?
 

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The adapter fitting arrived yesterday afternoon and I was finally able to test the line pressure. The result: a solid PASS! Next step: test the torque converter clutch solenoid. I would definitely recommend using a lower pressure gauge. An acceptable range of 20 psi translates to a sweep of just 5% on the 400 psi gauge. Very hard to read indeed.

Tools used
Oil Pressure Test Kit: https://www.amazon.com/gp/product/B0778XD4JT
0-200 psi Pressure Gauge: https://www.amazon.com/gp/product/B006JJ7D9W
M8 x 1.25 to 1/8" NPT Adapter: Amazon.com: Trico FA-1025 Brass Central Lubrication Straight Adapter, 1/8" NPT Female x M8 x 1.25 Male: Industrial & Scientific
 

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Well I removed and tested both the two solenoids called out in the manual (Torque Converter Clutch Solenoid and clutch pressure control solenoid C) and they both tested just fine. At this point the manual says to replace the transmission but the position of the TC clutch solenoid got me thinking. Because the TC clutch solenoid is located directly underneath the thermostat housing, it's possible that coolant could enter the upward-facing connector if one replaces the thermostat. And it just so happens that I did just that around the time this code cropped up. I don't remember if the CEL came on before or after the thermostat replacement but they were definitely suspiciously close and I never tried clearing the code.

Maybe I'm just clutching at straws but we'll see either way once I put the van back together and go for a drive. I'll keep y'all posted.
 

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My 99 run for about a year with the P0740 being erased/reset every time it came on. The code came up more frequent before the tranny died. The only symptom I had was shuddering during 40-50mph with tach under 2K. Other than that, it run fine. Until the tranny died on the freeway doing 70 mph. When I stopped it will not go in gear anymore. A few days after being parked in front of my house, I was surprised to have the van go in gear long enough I was able to park it inside my garage. Once the tranny got warm it started slipping off gear again. Got a new reman and its been running great for a year/7+K now. Good luck.
 

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Update: I put the van back together enough to take it for a test drive and the lock-up system worked perfectly. Over an hour of driving and multiple lock-ups with no problems. Whether I actually fixed anything is doubtful but cleaning and reseating the relevant connectors definitely didn't hurt. For now the MIL is off but we'll have to see how long it stays that way. Next up: replacing the head gaskets.
 

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But it might help you to know that back in the days when these ATs were subject to extended warranty due to the lawsuit settlement, if you went into a dealership with a P0740 code, they would not crack open the service manual or test anything. They'd order a new (rebuilt) transmission and swap it in.
How long is the extended warranty? I have a 2003 Ody that had P0740 once. I doubt it is covered but still good to know. Thanks in Advance
 

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How long is the extended warranty? I have a 2003 Ody that had P0740 once. I doubt it is covered but still good to know. Thanks in Advance
It is long gone. Not sure what years it applied to, but it was definitely at least on my '99 (4-speed). I think it was to 109k miles and 10 years.

When we got our first AT replacement, the problem was known to exist, so they offered to give me the part (Honda reman AT) for free, and I paid ~$600 to my dealer for labor.

Then some sort of recall came out, and they refunded my $600. That may have been the full lawsuit driven 109k/10 year thing.

Then my AT failed again, only 24k after installation. I think due to lack of having the replacement procedure flushing the whole ATF system, including the ATF cooler in the radiator. Replacement AT fully covered under warranty.

Many years, and about 80k later, it failed again. No codes that time, but it was flaring and I knew it was going. Well out of warranty, but I asked for goodwill from Honda of America. They did something to take about 25% off the price, which was nice, for a supposedly fully rebuilt AT with all new internals and solenoids. When I picked it up, I noticed oily dirt on the solenoids, called them on it and ended up getting that 3rd one for free (had already paid at that point, but got it refunded).

So you probably have zero hope with the warranty. Can ask for goodwill, which may be helped if you are a long time repeat Honda owner.

Following many countermeasures including a very good ATF cooler, Magnefine filters replaced every 20k miles, ATF single D+F every 10k miles, and careful driving, ended up making the 4th AT run very very well. Sold a few months ago, still running fine as far as I know.
 
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