Overdrive issue. Tstat, shift solenoid, trans temp sensor????

[Tampa_T4R]

Hey guys,

Just picked up a 1996 from a friend for cheap and it's great all around, but seems to have an overdrive issue. Happens in CC as well, and even worse actually. Could it be a bad Tstat that's not telling the PCM it's hot enough to operate? Does my temp in video look normal for fully warmed up? Trans temp sensor? Shift solenoid?

Here is a video, it starts at about 10 seconds in: https://www.youtube.com/watch?v=j8GjtDzKc00

My engine light was read to be IAC, and I do have a tear in my intake tube, but I don't see those two things causing this.

:thanks:

 

[Tampa_T4R]

Oh also, I've heard it can also be a bad PCM. Is there some type of "manual shift test" I can do to rule this out? I've seen it mentioned but couldn't find on search.

 

[phattyduck]

The thermostat is a mechanical part and doesn't tell the ECU anything. (Japanese vehicles use ECU = electronic control unit instead of PCM = Powertrain Control Module)

It is possible that the the ECU thinks that the engine is colder than it is (or the engine is running cold) by a bad temp sensor and that might disable the torque converter lockup. It is very rare for the ECU to go bad, so investigate other places first.

Step 1 would be solving your check-engine light issues. If you can get a code scanner that can read live data or a ScanGauge or UltraGauge you can read what the ECU thinks the engine temp is, along with fuel trims, etc. that could help you diagnose.

-Charlie

 

[Tampa_T4R]

The thermostat is a mechanical part and doesn't tell the ECU anything. (Japanese vehicles use ECU = electronic control unit instead of PCM = Powertrain Control Module)

It is possible that the the ECU thinks that the engine is colder than it is (or the engine is running cold) by a bad temp sensor and that might disable the torque converter lockup. It is very rare for the ECU to go bad, so investigate other places first.

Step 1 would be solving your check-engine light issues. If you can get a code scanner that can read live data or a ScanGauge or UltraGauge you can read what the ECU thinks the engine temp is, along with fuel trims, etc. that could help you diagnose.

-Charlie

Weird, through my searching I've only seen "PCM" used on this forum, whereas I'm used to saying ECU because I've worked on Hondas my whole life.

Anyway, I only ask the ECU question because I've seen a couple threads that have fixed this issue that way. Glad to hear that's rare. I have a scanner and plan to read the engine temp. These engines also have a trans temp sensor too, correct?

I'm going to dig into the valve cover gaskets this weekend so I plan to fix the current IAC code, clean the MAF, and TB.

Does the TPS throw a code when it is bad?

 

[phattyduck]

These engines also have a trans temp sensor too, correct?

I'm going to dig into the valve cover gaskets this weekend so I plan to fix the current IAC code, clean the MAF, and TB.

Does the TPS throw a code when it is bad?

There is a trans temp sensor, but you can only read it via OBD-II on '99 and later trucks, so you are out of luck on your '96 in that regard.

The TPS doesn't always throw a code when bad. You might have to check it with a multimeter if you suspect there is a problem with it.

-Charlie

 

[Bad Luck]

Hey guys,

Just picked up a 1996 from a fried for cheap and it's great all around, but seems to have an overdrive issue. Happens in CC as well, and even worse actually. Could it be a bad Tstat that's not telling the PCM it's hot enough to operate? Does my temp in video look normal for fully warmed up? Trans temp sensor? Shift solenoid?

Here is a video, it starts at about 10 seconds in: https://www.youtube.com/watch?v=j8GjtDzKc00

My engine light was read to be IAC, and I do have a tear in my intake tube, but I don't see those two things causing this.

:thanks:

Like phattyduck said, fix the CEL problem first. There's a slight chance that it could be causing your issue.

From the video it looks like you are going in and out of torque converter lockup judging by the rpms. Have you verified your transmission is filled to the correct level and the fluid is in good condition? If it is, then I would turn overdrive off (the button is on the side of the transmission gear selector lever) and counting the "shifts". You should see the rpm's drop for 1-2, 2-3, and then when the torque converter locks up. I think with the over drive off torque converter lockup in 3rd gear is around 45 mph.

Edit: I'd also get your dtc's read again to see the exact codes and if there are any transmission related codes set.

 

[brillo_76]

[MENTION=319302]Bad Luck[/MENTION] shouldn't we be hearing the engine running loader at 3k rpm. Maybe it's just my Tetanus 1. But my engine is alot louder at 3k then at 2k. I dont hear the engine at all changing. On level highway. I say that's not normal. Now around were a live there is no such thing as level roads for miles.. ,)

Sent from my SM-J337V using Tapatalk

 

[Tampa_T4R]

Like phattyduck said, fix the CEL problem first. There's a slight chance that it could be causing your issue.

From the video it looks like you are going in and out of torque converter lockup judging by the rpms. Have you verified your transmission is filled to the correct level and the fluid is in good condition? If it is, then I would turn overdrive off (the button is on the side of the transmission gear selector lever) and counting the "shifts". You should see the rpm's drop for 1-2, 2-3, and then when the torque converter locks up. I think with the over drive off torque converter lockup in 3rd gear is around 45 mph.

Edit: I'd also get your dtc's read again to see the exact codes and if there are any transmission related codes set.

Read the codes again and it’s still just throwing p0505 which is IAC, I’ll fix that this weekend along with the torn intake tube and reset my EFI.
Checked the trans fluid and it is full, but is a grey color, not red like it should be, maybe a trans flush is in order, I guess that could completely be my issue right?
I don’t have the correct scanner to check exact engine temp, but I get hot heat.
Everything shifts fine 1-2, 2-3, and will stay in 3rd with OD off. if I keep it at 60 on the highway, OD will work and doesn’t drop to 3rd like in the video.

 

[thegipper]

Post a picture of the tranny fluid on a white towel, it definitely should not be grey in color. If it is grey like you said, something caused it to turn grey like that. Either some additive was put in the system or something mechanical is failing.

If you do want to change out the fluid, I'd drop the pan and see how it looks. While the pan is off, you could test the shift solenoids, especially the solenoid that controls the TC lockup.

Search the forums and you should be able to find the procedure if you don't have a FSM.

 

[Bad Luck]

Read the codes again and it’s still just throwing p0505 which is IAC, I’ll fix that this weekend along with the torn intake tube and reset my EFI.
Checked the trans fluid and it is full, but is a grey color, not red like it should be, maybe a trans flush is in order, I guess that could completely be my issue right?
I don’t have the correct scanner to check exact engine temp, but I get hot heat.
Everything shifts fine 1-2, 2-3, and will stay in 3rd with OD off. if I keep it at 60 on the highway, OD will work and doesn’t drop to 3rd like in the video.

Does the torque converter lock up in 3rd? That is what that procedure was testing for.

 

[Bad Luck]

[MENTION=319302]Bad Luck[/MENTION] shouldn't we be hearing the engine running loader at 3k rpm. Maybe it's just my Tetanus 1. But my engine is alot louder at 3k then at 2k. I dont hear the engine at all changing. On level highway. I say that's not normal. Now around were a live there is no such thing as level roads for miles.. ,)

Sent from my SM-J337V using Tapatalk

All I hear is road/wind noise and the radio. I can't hear the engine at all.

 

[Tampa_T4R]

Does the torque converter lock up in 3rd? That is what that procedure was testing for.

Maybe I don't know what I'm looking for here, I've owned 24 cars and 22 of them have been manual, so I'm not too familiar with the TC.

What should I feel?

 

[Tampa_T4R]

Post a picture of the tranny fluid on a white towel, it definitely should not be grey in color. If it is grey like you said, something caused it to turn grey like that. Either some additive was put in the system or something mechanical is failing.

If you do want to change out the fluid, I'd drop the pan and see how it looks. While the pan is off, you could test the shift solenoids, especially the solenoid that controls the TC lockup.

Search the forums and you should be able to find the procedure if you don't have a FSM.

I was in fact using a blue shop towel and it was dark out, I'll post a picture of it on a white towel when I get home later. Thanks.

Would a failing TC lockup Solenoid throw a code?

 

[thegipper]

I was in fact using a blue shop towel and it was dark out, I'll post a picture of it on a white towel when I get home later. Thanks.

Would a failing TC lockup Solenoid throw a code?

Sometimes they will, sometimes they won't.

Dropping the pan and changing the fluid would be a good start.

While the pan is off, you can remove the 3 shift solenoids and bench test them.

There are three tests. One is a 12v test to see if the solenoid opens when you give it power. The next is to test the resistance of the solenoid and the last test involves applying pressure to it to see if it holds. If it otherwise shifts fine, you can skip testing two of the solenoids (the ones that control the 1-2 and 2-3 shifts). You need to test the 3rd solenoid that controls the locking of the TC.

Let me see if I can find the exact details.

 

[thegipper]

The solenoid should have an ohm reading of between 11-15 ohm. The solenoid should hold 71psi of pressure and you should hear the valve opening and closing when you apply the 12v.

If it fails any of the tests, replace it.

A/Trans shift Solenoid SL identify

See post#4 that shows you which solenoid is the lock up one (#3 in the diagram).

 

[Bad Luck]

Maybe I don't know what I'm looking for here, I've owned 24 cars and 22 of them have been manual, so I'm not too familiar with the TC.

What should I feel?

When the torque converter locks up you will see an rpm drop similar to the drop you would see during a shift. So if your torque converter is locking up you'll see an rpm drop from 1st to 2nd, 2nd to 3rd, and then 3rd to torque converter lockup with overdrive off and the gear selector in drive.

 

[Tampa_T4R]

When the torque converter locks up you will see an rpm drop similar to the drop you would see during a shift. So if your torque converter is locking up you'll see an rpm drop from 1st to 2nd, 2nd to 3rd, and then 3rd to torque converter lockup with overdrive off and the gear selector in drive.

With OD off:

So after it goes into 3rd, I should see ANOTHER drop in RPM, almost like it goes into another gear? This will tell me my TC is working properly or not working properly?
If it's not working properly and I'm not throwing a code, would it be likely that the TC is screwed?

 

[phattyduck]

With OD off:

So after it goes into 3rd, I should see ANOTHER drop in RPM, almost like it goes into another gear? This will tell me my TC is working properly or not working properly?
If it's not working properly and I'm not throwing a code, would it be likely that the TC is screwed?

When the torque converter is unlocked, RPMs will go up and down slightly with mild movements of the throttle. Kinda like a slightly slipping clutch.

When the torque converter is locked, RPMs will stay the same for changing throttle position (but will unlock if you apply too much throttle).

The torque converter will only lock in the highest available gear (3rd of OD is off starting around 45mph, 4th/OD if OD is on starting around 50 mph). And it does look/feel kinda like a shift to another gear if you watch the tach.

-Charlie

 

[Tampa_T4R]

When the torque converter is unlocked, RPMs will go up and down slightly with mild movements of the throttle. Kinda like a slightly slipping clutch.

When the torque converter is locked, RPMs will stay the same for changing throttle position (but will unlock if you apply too much throttle).

The torque converter will only lock in the highest available gear (3rd of OD is off starting around 45mph, 4th/OD if OD is on starting around 50 mph). And it does look/feel kinda like a shift to another gear if you watch the tach.

-Charlie

If the bold above is true, I think my TC is locking just fine. If I have OD off and in 3rd at ~60mph and i lightly increase throttle, RPMs will increase without any slipping to higher RPM. If i'm in '2' in 2nd gear, and I lightly increase throttle, I do see the slight slipping of RPM before it changes to 3rd.

I don't however, remember the "change of gears" feeling when the TC locks after getting to 3rd with OD off.

This guy had exactly the same issue as me and fixed it with a new ECU: Shifts in-n-out of OverDrive... Look at post #7 for solution
Can't there be more than just torque converter lockup that would cause my issue because of a bad ECU?

Thanks guys, I really appreciate you time.

 

[Bad Luck]

With OD off:

So after it goes into 3rd, I should see ANOTHER drop in RPM, almost like it goes into another gear? This will tell me my TC is working properly or not working properly?
If it's not working properly and I'm not throwing a code, would it be likely that the TC is screwed?

You should see another drop in rpms when the torque converter locks up. If you don't see another drop, then the torque converter isn't locking which could be a failing torque converter or a weak solenoid.