Need advice code 648 on 95 explorer

[electronicsguy]

Ill start at the beginning. A few months ago my explorer had trouble going into reverse and there were 2 different times that the od off light would start blinking but would go away by itself without having to reset the pcm, I immediately bought a filter and fluid and had it changed. Everything was perfect until last weekend I was going 80 on the highway and the light started flashing and stayed this time. Then the next day I did something really stupid. We were pulling a trailer with the ac on max on a 95 degree day and I would usually kick overdrive off to keep from being too hard on the tranny but since the transmission was in limp mode (i didnt realize this at the time) I couldnt switch it out of overdrive. On the way back home it revved up like it was in neutral and I had to pull over to the side of the road (im guessing i overheated the tranny) I shut it off and started it back up and it was fine other than the light flashing. I had the codes scanned the next day and I had 335 and 648, I fixed code 335 by changing the dpfe (egr pressure sensor) but the code 648 is incorrect 4th gear ratio. I had a transmission shop tighten the bands today for intermideate and overdrive but they said that didnt help and they wanted to pull the tranny apart and start rebuilding. My question is, is there any way I can check for a bad servo seal, servo, solenoid or anything else without pulling the pan off the tranny? Also if I reset the pcm and leave od off, the code never comes back and it drives fine other than my gas mileage sucking from not having overdrive. What are the chances I can get by for awhile by leaving overdrive off and there a way to make it default to od off when I start it in case I forget to hit the button one day? Also it does seem to shift into overdrive but the tach bounces about 300rpm while driving on the highway right before it sets the code, maybe a clue?
thanks
Mike

 

[PopRichie77]

When you think it is shifting into OD it is probably the torque converter locking up. No, there is no easy way to lock OD off. All solenoids are inside the pan, the 2 servos can be changed but on a scale of 1 to 10, it is a difficult level of 8 or 9 especially for a novice, which you must be or you wouldn't be asking the question. The problem could be a solenoid or an internal failure.

 

[snoranger]

When you think it is shifting into OD it is probably the torque converter locking up. No, there is no easy way to lock OD off. All solenoids are inside the pan, the 2 servos can be changed but on a scale of 1 to 10, it is a difficult level of 8 or 9 especially for a novice, which you must be or you wouldn't be asking the question. The problem could be a solenoid or an internal failure.

You're joking, right?

What's the little button at the end of the shifter stalk for?

 

[PopRichie77]

Yes, with the button but it resets every time you restart and that is a momentary contact switch. I thought you wanted to get around the reset when starting?

 

[snoranger]

Yes, with the button but it resets every time you restart and that is a momentary contact switch. I thought you wanted to get around the reset when starting?

I'm looking for a thread from a few years ago, someone made a circuit to default it to OD off on startup.


Found it:

http://www.explorerforum.com/forums/showthread.php?t=251513

 

[PopRichie77]

Yes, that should work fine but you wanted some easy way, however this may be easy for you.

 

[snoranger]

Yes, that should work fine but you wanted some easy way, however this may be easy for you.

With a screenname like Electronicsguys, it should be easy for him.

 

[electronicsguy]

snoranger I know what the OD off button is for, but It resets every time you restart the vehicle and if I forget one day when im in a hurry ill set the code again once it hits overdrive then it will be back in limp mode and shift hard until I can unhook the battery cable and let the pcm reset. I was able to get around that last night with a simple circuit I threw together, but im wondering if I can get away with driving it without overdrive or if whatever is causing the problem will end up eating up the rest of the tranny. Im not much for pulling the pan and replacing parts inside the tranny but I have a mechanic who will do that for me if need be but what im wondering is if anyone has the troubleshooting procedure from alldata and if I can check the voltages at a harness somewhere with the tranny fully assembled or do I have to drop the pan and check everything on the harness inside the tranny (wouldnt make much sense to me because I couldnt have it running for testing). I reset the codes again last night and took it for a drive, it was at 2200rpm at 65mph when the od off light started to flash, it only took about 5 sec and that speed for it to happen. Sometimes the rpms will vary from 2200 to 2500 back and forth until the od off light starts blinking. Maybe a clue?
Thanks for all the help
Mike

 

[PopRichie77]

The RPMs are changing because 4th gear (OD) is slipping. A code 648 does not refer to any electrical problem, except the solenoids.
Quoting directly from the 4R55E ATSG transmission manual, Code 648----SS1, SS2, SS3 or internal parts--4th gear error--No 4th gear--improper gear selection depending on failure or mode and manual lever position. Shift errors may also be due to other internal transmission concerns (stuck valves, damaged friction material)
I have no data on voltages.

 

[PopRichie77]

By the way it is not necessary to disconnect the battery to reset the computer, you only do this to removed the stored code. Just turn the engine off, wait a few seconds and restart, the computer will be reset, no limp mode and no flashing OD light. The OD light will not flash again until the computer sees the trans error again.

 

[electronicsguy]

are the shift solenoids external or inside the pan? If they are external ill pull them off and check them one at a time. Thanks for all the great info. For some reason my explorer wont come out of limp mode and stop flashing unless I unhook the battery cable. I let it sit overnight and it was still flashing od off this morning so im not sure why but I just kept an 8mm socket in the center console for when I forget to turn od off before leaving lol, but I dont have to mess with that now because I made a circuit with a 555 timer IC to pulse 12v to the od off button 7 seconds after im done cranking the engine so od is always off and all is well til i can figure out whats wrong with this thing.

 

[PopRichie77]

The solenoids are inside the pan. I could be wrong about the 4R55E computer resetting, I do know it does on the 5R55E. I can find no information on this and I just assumed it would work on yours. Every time I assume something, it turns around and bites me. I know better but it happens anyway.
Nice job on using the 555 timer IC, when you are sitting here looking at a computer monitor, you have no idea what skills the other person has. Pulling the pan isn't to bad you just need a large container to catch the fluid,of course you may get a fluid bath. The solenoids are held in place with a bracket and they just slide into the valve body. They can be checked with an ohm meter, there is an ohm range for them, some are different, ss1,ss2 and ss3 are the same, they are shift solenoids. also 12 volts can be applied to each one after removing and you can hear or feel the movement inside. If any don't ohm out or don't move it is bad. This isn't a 100% check as it can ohm ok and click ok but have internal leakage.

The ohm reading for SS1,2,3 or SSa,b,c, depending on who's chart you are looking at is --- 22-48 ohms
There are other things inside the trans that can cause the problem also, leaking OD servo, bad OD band, failed OD sprag. Valve body problem.

 

[electronicsguy]

Thanks for all the help! Im gonna pull the pan tomorrow and remove the solenoids and put 12v across the coil of each while running a 5 amp load thru the switched portion and see if there is any voltage drop, if the switched contacts are leaky that should show it hopefully. I also had another sick thought, the shop that changed my filter and fluid is one of those "good ole boy" types of shops that mainly works on older cars, im wondering if they put dexron 3 in there instead of mercon 5, im going to flush it and put in mercon 5 and some lubegard and see if that helps. Ill post the results.
thanks again,
Mike

 

[PopRichie77]

Don't understand your 5 amp load, the solenoids contain a coil which will not withstand a 5 amp load. There are no contacts in them.The shift solenoids are hydraulic flow solenoids, either on or off, when activated a port opens an redirects the fluid flow. Plus 12 volts is supplied to them when the key is turned on, the computer operates the negative side of the coil, which never goes to zero. Do not apply 12 volts any where that will feed back to the computer. Only test the solenoids after they are removed. You should get a 4R55E ATSG transmission manual. There are 6 solenoids in the trans, 4 shift solenoids, 1 EPC (electronic pressure control) which is constantly modulated by the computer and a TCS (torque converter solenoid) which is also constantly modulated by the computer. These are fully computer controlled transmissions, the manual valve only redirects fluid pressure within the valve body, all gear selections are done by the computer. The DTR (digital transmission range ) sensor is connected to the shift lever and tells the computer what gear has been selected. Again I must say get the manual, seeing a pic and reading your self is easier than me trying to explain as it is easy to error or forget a caution.

 

[electronicsguy]

Thanks, Ill grab a manual before I drop the pan. My bad on the solenoid thing, i was thinking it was like a lot of solenoids in cars that are actually relays but they are called solenoids, not one that actually has mechanical movement like these. I was picturing one with a coil and a set of normally open contact that close when you put 12volts across the coil. thanks for the heads up on that.