ssumners

I am trying to verify the electrical is working correctly on this 94 Chevy K1500 before putting this 4l60E back together again after my recent rebuild. I pulled the trans pan cover to inspect the solenoids since the truck had no 1st or 4th gear. With the truck ignition in run I took a solenoid I know works and plugged it into the 2-3 shift connector and the solenoid energizes (I hear a click). I take the same solenoid and attach it to the 1-2 shift and nothing happens. Both 1-2 and 2-3 leads show 12 V on the voltmeter. The wiring harness in the trans is new(it isn't installed but just plugged into the vehicle harness connector. 2 different local shops had taken a look at the truck and they said there were no codes. Any help finishing this would be appreciated.

Info included regarding wire harness 1-2 and 2-3 resistances -

Allan In NE

Are you saying that after the transmission rebuild, you then had no 1st or 4th? Or, are you still just now putting it back together and are trying to verify everything?

I need to know where you're at here.

Allan

ssumners

Timeline: I did the rebuild complete and drove the truck - no 1st or 4th. Took the pan cover off to inspect the electrical - suspecting 1-2, 2-3 solenoids or wiring harness defective. With truck in "run" neither 1-2 or 2-3 solenoid would energize when unplugging a solenoid and plugging it in to the trans harness. 1-2, 2-3 Solenoids were verified good themselves but I bought new ones anyway along with a new transmission harness. Now the 2-3 energizes in run but the 1-2 does not even though voltage at the 1-2 solenoid plug measures same as the truck battery. I assume the 1-2 solenoid is supposed to energize with the truck in run - my intent is to verify that 1st before putting it back together and finding it still doesn't work correctly.

Allan In NE

Okay, gotcha.

Bear with me 'cause I'm gonna throw a whole litney of items at ya to try and help you "think this thru". And, it's gonna be a bit 'wordy.

All computerized circuits concerning the downstream components such as step motors, solenoids, etc. are "ground searching". That is to say, they 'power up', but lack a ground circuit until the computer provides that ground. I.E.....An EGR solenoid will not operate until the computer says it's okay and "turns on the ground path" to activate that solenoid.

Further, the computer cannot see mechanical faults. It can only read in terms of electrical connectivity and what any one component is doing 'electrically' at any given time (state).

You turn the ignition to 'run'. The computer immediately goes into default......it's operating solely on it's built in ROM; the prewritten insturctions on that chip. During start up and after it sees an ignition signal, the computer then goes into loop, be it open or be it closed depending on the reading at the coolant temp sender.

See where I'm going with this? The default state for this transmission is second gear. Solenoid A is off and solenoid B is energized.

But, let's get back to your truck. Did you have that valve body off the case? Did you pull the valves and did you get it back together correctly?

Further, and more importantly, did you get the bolts back in their proper locations? The bolts are different lengths and cannot be just 'put in any hole'. If a long bolt was inserted in in a 'short' hole, the operation of the transmission is compromised.

Point two: When I have one of these jokers that is playing with my head, I walk away from the thing and come back to it with the attitude that I've never seen this truck before. FORGET ALL THAT HISTORY IN YOUR MIND. It's a brand new problem and ya just simply don't have a first or fourth gear.

Okay, sure sounds like a shift solenoid A, doesn't it? If you are absolutely confident that the valve body is correct, put in two good solenoids and button 'er up. CLEAR all the codes and drive the truck. If you still don't have 1st and 4th, proceed.

In first gear the band is NOT applied, but it is ON in 4th. Likewise, in 2nd the band IS applied and NOT in 3rd. So, it's a fairly safe bet that the band is coming on and going off as it should. That points us right back to the problem being electrical.

I would backprobe the chasis electrical connector for continuity clear back to the ECM connector. If all is as it should be, at that point I'd really suspect the ECM....................However, this very, very rarely happens.

Let us know how this turns out?

Allan

ssumners

Thanks for the analysis. I plan to get things put back together this weekend and post an update.

ssumners

All gears operational! I had fears of this never being quite right with out expensive shop work.
Examining the trans fluid it is darker than new fluid. I don't smell much of a difference between the two. During the diagnosis the truck was working a bit harder since it was starting in third gear so I'm guessing that caused some excess slip between the clutches. Recommended flush or not too much of a concern?