Disappearing Electrical/Transmission Problem

[DieselAdict]

This all began about a month ago. A very minor hesitation, or so I thought, of the transmission going into gear. Progressively getting worse I realized that it was starting in 3rd gear. It began to lock up and try to shift into overdrive at about 5-10mph. The was then parked to save transmission components. The only way to drive it was manually starting in 1st and shifting though the gears. Once in OD and locked up I was able to drive it home. I started with tracing all the possible culprits. Tapped into the harness and tested the overdrive and lockup solenoid. Came out to be bad and so it was. No Fix.

I then Pulled the whole wiring harness on top of the motor and went through it. Checking for shorts and bad connections. Found a few questionable things but had no apparent problems. Fixed them properly anyways. In the end no fix.

Continued down the line checking the codes after I replaced the Solenoid. The only code that was not normal was the P0720 Output Speed Sensor Intermittent. Replaced it. No Fix

I followed through testing all the sensors and solenoids one at a time in the transmission. In which all ended up reading like the where bad. Replaced the Governor transducer and solenoid. No Fix

So now up the chain the pcm. Started testing other things such as the throttle position sensor. Readings came out correct on the sensor when I checked the resistance. Checked the input voltage and found that it was only seeing .7 volts. I traced it to the pcm and found no shorts. So now just one more thing pointing at the pcm.

I broke down and purchased one from a local guy in Bloomington Indiana that rebuilds them. This pcm was originally off of a manual and then converted to auto by the guy I bought it off of. It Fixed A LOT But!

At first I thought it was a done deal. I was able to drive the truck again. Checked a lot of voltages and the where correct such as at the supply voltage for the tps. Now at a solid 5 Volts. The only thing I noticed was when I tap on the brakes it should kick out of overdrive, it didn't. I don't know for certain if this was a problem before as the computer farther went down hill, but did work before all of this started. To add to it, it is hunting at the slightest throttle movement in and out of lock up. I have no idea if any of these to problems are related. I have checked the tps and its good brake light switch good. Even traced the wiring and checked it to the pcm all fine. I'm to the point where I am assuming that it is related.

After a solid day of driving around town and out to the farm it happened again after sitting for a couple of hours. Tried to start in 3rd gear again. No trying and shift into OD and lock up at all though.

I have been able to drive the truck despite the problem. Here is the kicker it only happens maybe 1 in 4 times the truck drove. If the problem arises I can shut the truck off and It starts fine.

Today I rechecked the codes as I should have done a week ago. Still getting the P0720 for the Output speed sensor. Ok so I completely replace the wiring not including the connectors. It Did nothing. I am going to check the codes again tomorrow see if i got rid of the p0720.


So what I really need is some insight on where to look next. Could this still be a pcm problem? I have spent countless hours and hundreds of dollars trying to figure this one out. I consider myself well versed when it comes to most automotive and electrical problems, but I am need of a guru that has been here before. Please Help

 

[sterkel]

Is this a 47re or 47rh?

 

[DieselAdict]

It's a 96 so 47re.


Sent from my iPhone using Tapatalk

 

[DieselAdict]

So today I cleared the Codes. The P0720 for the output speed sensor was still there. Continued digging through all wiring not just for the transmission but all the abs wiring and etc. Trying to find anything. Fairly certain that the base problem is the pcm that I installed. I contacted the the guy about getting a different one an exact replacement not one that has been converted from a manual. So after another 4 hour round trip I should have another pcm sometime next week. I would really like some input.

 

[jasonc]

I couldn't pay attention to read all that, tapping the brakes releases lockup still stays in overdrive. Sounds like what my buddies truck was doing, replaced the tps sensor solved it. Where do you have the tv cable set at?

 

[DieselAdict]

I have already checked the tps and it is good... just replaced it 6 months ago to further solidify the conclusion. The tv is set for the later shift points without bending the brackets can't get to the truck since I'm at work otherwise I'd have a better answer. It at times will when I tap on the brake come out and then go right back in. Just quick enough for you to notice it's doing it. The real big issue is it starting in 3rd gear, but I can't help but think that the two issues are related. Checked the codes again still have the p0720 for the output speed sensor. Would someone be able to explain the full function of what the sensor is used for. I have a general understanding but not knowing what it can effect is still troubling.


Sent from my iPhone using Tapatalk

 

[DieselAdict]

So I have solved my problem. It was an elusive and expensive fix to say the least. The root cause was an auxiliary power trailer brake wire that was grounding out. This wire was a 10 Gauge wire, which can pull some serious amps. Needless to say it was not fused... probably due to an inexperienced kid dealing with electronics. It completely melted the sheathing. Pulling that kind of power it put an extreme strain on the alternator. With an older almost worn out alternator, it died. Still producing current it was, but not well. A lot of AC current was getting ran through the system. Fried the PCM. So a new alternator and the original PCM out of my truck, just remanufactured. My truck drove perfect for the first time in over a month.

I just wanted to finish this thread to show how something so simple can wreak havoc on an electrical system... Hopefully this helps the next guy.

 

[biggy238]

Awesome find and follow up.

Sent from my XT1575 using Tapatalk