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PO56 - Transmission Input Speed Sensor - solenoids?

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Hello all..

I'm a new guy on this forum, but have been working on my '95 Eldorado for years. I'm throwing a dreaded PO56 code Input Speed Sensor, and missing between 2-3 and 3-4 gears. I had a self-rectifying problem when it was thrown before and wouldn't go into 4th. Does anyone know if a shift solenoid [and all problems therof] could be causing this? It's just a shot in the dark, knowing that both solenoids could have to be bad in this scenario. Your thoughts? (4T80E transmission/No ETC)

Thanks and Cheers!

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When my shift solenoids went south in my 94 Concours, I also had a P056. After I replaced the solenoids the P056 went away for a long time. If your shift solenoids are bad you should have a P029 and/or P094 code.

Are you throwing any other codes? Are any of the codes "current" or just "history"? Give us more info.

You really need to get a shop manual if you plan to keep it and keep working on it. Some codes are related but you have to be careful which one to deal with first. A manual will have the diagnostics for each code and is invaluable if you work on the car yourself. This website has a wealth of information and people willing to help in any situation, but you need a manual. Also the engine in a 95 Eldorado should be a 4.6 not a 4.9.

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Hey Paul

The only current code is the PO56. There are no other codes in the history but RSS codes, which have been taken care of already. My presumption on the shift solenoids, lay in theory. When the code first appeared last November, it was because of my punching the gas and a (presumed) 3-4 solenoid failure. The car just wouldn't go into OD. That problem rectified itself overnight by sheer miracle. I punched it recently and it did the same thing as last.

This time, no overnight miracles and the car is missing intermittently in between 3-4, until she catches up.

Your thoughts?

Oh, yeah. I must have had temporary dyslexia when I put the 4.9 in for a Northstar. Rough week when I joined.


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You need to check the wiring to the sensor for a ground or open circuit. Make sure there are no wires next to the spark plug wires, this will cause the problem. There is a plug that goes into the tranny, check that connection. You also could have a PCM problem causing it. Check the PCM plug connection. Make sure the battery connection is clean and tight.

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Good ideas Paul. That sounds like a little less fun than crawling under and pulling the valve body out, but I'll give it a whirl. :) I haven't had much time to get a peek at it, but that makes sense to me. I've seen a bad ground on the negative side of the frame that needs to be cleaned up. I may as well give her a work-over and check them all. I'll be back with my findings. Thanks!

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