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Discussion Starter · #1 · (Edited)
I've been following this forum since I bought our 2006 Honda Pilot EX-L AWD (new) and it has been extremely helpful. I’m hoping some here can give me some insight into my transmission problem.

This vehicle has been reliable and has few (small) issues but at 169,000 miles we had a radiator problem where transmission fluid leaked into the coolant. After the repair, the vehicle was working great BUT now I’m having problems where the transmission is not shifting from 2nd into 3rd.

I did not get a code initially but after my third transmission fluid change I am now getting two codes:
  • P0752 - Shift Solenoid Valve A Stuck ON
  • P0747 - A/T Clutch Pressure Control Solenoid Valve A Stuck ON
After starting the vehicle, the transmission will flare when trying to shift into 3rd gear and will only dve in 1st or 2nd gear (limp mode?)

Digging through the Cardiagn Automatic Transmission repair manual I am wondering if:
  1. the transmission is really toast,
  2. the solenoids are gunked up and need to be cleaned (or replaced) - there are two solenoid codes now,
  3. something else?
I have a Foxwell NT510 Elite scanner coming where I hope to test some of the solenoids before removing them.

Backstory

While on a road trip a 3 weeks ago I noticed the transmission slipped a couple of times. A few miles later the transmission disengaged and I had no power (like I was in neutral). I pulled over and immediately found fluid leaking out of the radiator. I checked the transmission fluid and it didn't even show on the dipstick. There were no indicators showing any issues when I pulled over.

I had the car towed to a local mechanic and found out that the transmission fluid was leaking into the coolant via a broken seal in the radiator (I was told is was one-way: transmission into the radiator but not the other way around). When what was left of the transmission fluid was drained it was black and stunk up the garage (the mechanic said he has never smelled anything that bad). There was little debris on the drain magnet - nothing out of the ordinary I was told. The radiator was replaced and the transmission fluid was drained/filled twice. And the transmission was working great!

I had instructions to get the transmission fluid changed again in several weeks.

All is well until a couple of days before my scheduled transmission fluid change.

My wife was driving the car and had an issue where shifting into 3rd it flared. I think it dropped into 1st gear where she limped into a side street. I found that it would drive in 1st and 2nd with no problem. I took the car into my local mechanic for inspection. There were no codes and other than the transmission fluid being darkish nothing was found. I was told the transmission needed replacing. While driving the car a few blocks back to my house I noticed that it DID shift into 3rd gear once (not smoothly and I couldn’t get it to do it again). Huhn. So I started doing some research and changing the transmission fluid myself to see if that would help the problem.

ATF change #1
Fluid was very dark. Almost nothing on the drain magnet.
During the road test, the transmission would flare when shifting into 3rd. After releasing the gas pedal the transmission would drop down into 2nd or 1st gear. I couldn’t get it to flare again but it would happily shift between 1st and 2nd as needed.
After 15 minutes I did get the blinking D indicator and pulled stored code P0752 (Shift Solenoid Valve A Stuck ON).

ATF change #2
Fluid was still darkish. Drain magnet was fairly clean except for two tiny shards of silver metal (yikes).
The transmission behaved the same as after the 1st ATF change. Again, code P0752 was stored.

ATF change #3
Fluid was looking much cleaner. Drain magnet was clean.
I changed out 3rd gear clutch pressure switch (purely a guess).
I also reset the ECM by pulling off the battery terminals for 5 minutes.
The transmission behaved the same as after the other 2 ATF changes BUT this time in addition to code P0752 I also got code P0747 (A/T Clutch Pressure Control Solenoid Valve A Stuck ON).

Now I'm pondering what to do next...
 

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Could be your transmission is toast, but a not outrageously expensive thing to try first, as you did, is swapping out the 3rd (and 4th) shift solenoids (aka pressure switches). Did you use OEM only?

Then keep doing ATF drain & fills a few times, driving a few miles between each, until your fluid looks good.
 

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Discussion Starter · #3 ·
Could be your transmission is toast, but a not outrageously expensive thing to try first, as you did, is swapping out the 3rd (and 4th) shift solenoids (aka pressure switches). Did you use OEM only?

Then keep doing ATF drain & fills a few times, driving a few miles between each, until your fluid looks good.
The transmission fluid has already been changed 4 times total and it is looking clean now.

Shift solenoids (actuators) are different than pressure switches (detectors). Shift solenoids are designated Valve A, Valve B, Valve C, Torque Converter Clutch while pressure switches are clutch-specific (1, 2, 3, etc.). I have already changed out the 3rd shift solenoid. We have since tested the part we removed and it is functioning properly so that was definitely not the problem.
 

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Now I'm pondering what to do next...
In addition to the advice you've gotten and the plans you have underway, I think it's appropriate to work out a contingency plan. You may get lucky and find a minor problem that is easily fixed. If not, you're looking at a significant investment to keep your Pilot rolling. That's not a simple decision on a 15+ year old vehicle.

For what it's worth, it seems unlikely to me that there was zero cross-contamination between coolant and ATF. Black and smelling terrible is not normal. If it was pure ATF and burned that badly, I think you would have seen problems previously. Contamination seems a more likely explanation.

If you decide to consider investing in a new transmission, I suggest getting a second opinion from a transmission specialist, preferably one that knows Honda.
 

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Discussion Starter · #6 ·
Well... my issue has not changed.

One interesting observation is that when it does flare going into 3rd gear it is actually in 1st gear as I can accelerate if I get RPM's high enough. Reducing speed the transmission will shift back into 2nd. I'm not sure if that is part of "limp mode".

What I did:

Testing
Using a Foxwell NT510 reader with Honda software, all tests passed for Shift Solenoids and A/T Clutch Pressure Control Solenoids.

I cleaned the grounding contacts for the engine ground cable, going as far as changing the cable itself. Before changing the engine ground cable we measure the resistance from the negative battery terminal to the engine block and it was 0.2 ohms.

I have removed, cleaned, and tested most of the solenoids.

Code P0747
I removed the A/T Clutch Pressure Control Solenoid Valve A/B assembly (#7). It was clean.
Both solenoids measured approximately 5.5 ohms (within the expected range of 3-10 ohms).
Testing with a battery the solenoids moved as expected. We further cleaned the contacts for good measure.
Pipes (#1 and 2x #2) were clean, no debris in the screens.
Gasket and pipe o-rings were replaced when reassembled.

Code P0752
I then removed the solenoid valve cover to reach the switch solenoids.
This compartment was not clean, there was burnt ATF residue on everything - which I thought was abnormal.
All four solenoids A, B, C, and torque converter) were removed, cleaned, and measured approximately 17 ohms (within the expected range of 12-25 ohms).
Testing with a battery the solenoids clicked as expected.
When re-assembling we swapped brown solenoids (A/B) and black solenoids (C/torque converter) to see if the problem moved with them.

140031
 

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When the doctor looks at his watch, either the shift has ended :) or he's calling time of death. In your case it may be both. :(

 
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