Up shift problem

[CC Rider]

1995 4 banger Auto

Truck is at the shop now for the second time
Not upshifting correctly
Have to let foot off peddle to get it to upshift.
If you do not release peddle presure it will keep reving and not shift.
OD light flashing most of the time.
Tranny Tech finding nothing wrong - this is a good shop.

Any help would be apreciated!
Thanks

 

[ZSK]

If the O/D light is flashing the tranny is throwing a trouble code the tech should be able to fix it according to the code.

 

[CC Rider]

If the O/D light is flashing the tranny is throwing a trouble code the tech should be able to fix it according to the code.

I agree !
I'm getting ready to call the shop. They keep saying it must be an electrical problem ( don't understand that statement)

No vacuum diaphragm on this year so is there some sensor that tells the tranny to shift?

 

[MAKG]

The PCM tells it when to shift.

Of course it's an electrical problem. If these guys get confused by high-falutin' words like "resistance," I'd strongly suggest a different shop. The days when everything was adjusted mechanically are long over; it's no longer remotely acceptable to punt repairs with a magical "electrical" label.

Keep in mind that diagnosing this problem may require significant engine diagnosis.

 

[CC Rider]

The PCM tells it when to shift.

Of course it's an electrical problem. If these guys get confused by high-falutin' words like "resistance," I'd strongly suggest a different shop. The days when everything was adjusted mechanically are long over; it's no longer remotely acceptable to punt repairs with a magical "electrical" label.

Keep in mind that diagnosing this problem may require significant engine diagnosis.

That's what I was thinking ( PCM) but was hoping some sensor I could not identify was doing the magic :^)

I'll see if Pick & Pull has a doner this weekend.

Thanks

 

[CC Rider]

OK the shop did find a code and the 3/4 shift selonoid could be the issue.

I say could because he said at the same time the PCM could be causing the code if the PCM is damaged or not working properly.

Sound remotely familiar :^)))

Thanks

Check book in hand :^(((

I hate having others work on my stuff

 

[MAKG]

You need more diagnosis. No code is sufficient to condemn any sensor or actuator. Codes check CIRCUITS. And both your PCM AND your 3/4 solenoid could be fine. Sometimes (FAR more often than people think), the problem turns out to be a broken wire or poor connection.

 

[CC Rider]

Thanks for the info - I did pass this allong to the tech and he agreed

 

[Bent Bolt]

You need more diagnosis. No code is sufficient to condemn any sensor or actuator. Codes check CIRCUITS. And both your PCM AND your 3/4 solenoid could be fine. Sometimes (FAR more often than people think), the problem turns out to be a broken wire or poor connection.

Almost. There are 2 basic types of trans codes. Some are Electrical faults such as P0755 which is a SS2 solenoid circuit failure. This code is only set if there is an electrical failure anywhere from and including the PCM, wire harness ,solenoid.

A code of P1756 is a shift solenoid No. 2 functional failure ,mechanical or hydraulic failure from and including the solenoid,valve body or clutches/band. A DTC P1756 cannot be set by a electrical failure just as P0755 cannot be set by a failed clutch function.

So whatever code was set in CC rider's truck should fairly easily direct a competent tech in the right direction.

 

[MAKG]

Even functional tests can flip codes due to wiring faults. There must be some sensor -- and wires to it -- involved. In this case, I'd guess the IDM and VSS circuits (both of which should trip their own P codes if problematic, but might not if they are in range but just wrong). All P codes are flipped by the PCM, so a PCM fault can flip them erroneously (though this is rare).

OBD-II diagnostics are substantially more reliable than OBD-I, but they still are not perfect. There is little redundancy in automotive diagnostics like there is on aircraft and spacecraft. That's why they can get fooled.

 

[Bent Bolt]

Well CC, what did you find out ???