Riddle me this, a transmission conundrum

[JOES66FURY]

Specifics: 1999 Dodge Ram 1500 4X4. 360 V8, automatic.
Problem: Check engine light code P1756. Engine will not up shift. Common cause - governor pressure sensor not between 5-10psi
.

.

I took a shot and changed the speed sensor...it worked. The sensor I pulled had a lot of thick metal sludge stuck to it. I replaced it and it started shifting just fine.

what is odd is that the speed sensor is not listed as causing a p1756 code....

Thoughts?

[STINEY]

Re: Riddle me this, a transmission conundrum

Speed sensor not telling the cpu to increase pressure, thereby throwing an incorrect code?

[Tazracing]

Re: Riddle me this, a transmission conundrum

without input from that sensor the ecu(brain) doesn't know how fast your going and time to shift

[JOES66FURY]

Re: Riddle me this, a transmission conundrum

Right Mark, but why throw a code that doesnt reference the part?

Stiney, does the speed sensor pick up speed to the CPU and the CPU adjusts pressure to the gov press sensor?

[Bamfster]

Re: Riddle me this, a transmission conundrum

I'd be more concerned with the metal in the pan .....

[squirrel]

Re: Riddle me this, a transmission conundrum

The sensor is magnetic, it collects metal from the fluid, seems to be common.

Great diagnosing job Joe, you figured out what the computer was trying to tell you, even though it's too dumb to say it properly

[TC]

Re: Riddle me this, a transmission conundrum

I'd be more concerned with the metal in the pan .....

The sludge is normal as long as there's no big chunks in it. On my '99 Z28 everytime I did a trany service the magnet in the pan always had a bunch of metal sludge on it, I would just clean it real good and replace the filter and add the new trans fluid and I was good to go.

How does that saying go, if it's working, don't break it. ;)

[JeffMcKC]

Re: Riddle me this, a transmission conundrum

This really happens a lot in real life. EGR codes can be thrown with a Vacuum leak EGO codes because of a vacuum leak or a exhaust leak, shorted wires going to sensors. The code leads you to the area to test, not what to change

[TheSilverBuick]

Re: Riddle me this, a transmission conundrum

This really happens a lot in real life. EGR codes can be thrown with a Vacuum leak EGO codes because of a vacuum leak or a exhaust leak, shorted wires going to sensors. The code leads you to the area to test, not what to change

That's why Autozone is in trouble with the law in a few states. They do their "free code scan" in the states that still allow them to, and the dip behind the counter (sometimes called the store manager even) sells them a part based on that code. I refused to do that, Lean/Rich codes were common, most the dips behind the counter would sell them an O2 sensor, I'd tell them to go home and look at the wiring, making sure the wires to the sensor weren't burnt, then check the air filter and vacuum lines, etc first. Same with speed sensors, etc.

[Tazracing]

Re: Riddle me this, a transmission conundrum

Right Mark, but why throw a code that doesnt reference the part?

Stiney, does the speed sensor pick up speed to the CPU and the CPU adjusts pressure to the gov press sensor?

because there shouldn't be metal in the pan there for it not need a code

[STINEY]

Re: Riddle me this, a transmission conundrum

I don't know for sure Joe, but I've read that computer controlled transmissions do regulate pressure based on speed/load, in order to be more fuel efficient.

The computer has to get that info from something, speed sensor would about have to be part of the picture.

[JOES66FURY]

The sensor is magnetic, it collects metal from the fluid, seems to be common.

Great diagnosing job Joe, you figured out what the computer was trying to tell you, even though it's too dumb to say it properly

Yeah, it seemed odd that it would shift but only at high RPMs, seemed to me that if the pressure wasn't proper, it wouldn't shift at all...thats why I took a shot with the speed sensor. it seems to be all sorted out at this point...no more issues...thank goodness

[IndyShiftman]

Governor pressure solenoid and sensors are VERY common in going bad. You will need to drop the valve body to replace them. Definitely replace both if you don't want to do the job twice. Good luck in getting the park rod back in place.

[JOES66FURY]

Indy,

The problem is getting worse, but what I find odd is that it only does it when it is hot. When cold it shifts fine. I assume that has to do with the fluid viscosity. If I am driving I either have to back off the throttle to get it to shift, or put it in neutral and give the throttle a blip and then put it back into get to get it to shift.

Can you elaborate (or anyone) on the park rod? Tips and tricks?

[IndyShiftman]

Indy,

The problem is getting worse, but what I find odd is that it only does it when it is hot. When cold it shifts fine. I assume that has to do with the fluid viscosity. If I am driving I either have to back off the throttle to get it to shift, or put it in neutral and give the throttle a blip and then put it back into get to get it to shift.

Can you elaborate (or anyone) on the park rod? Tips and tricks?

Typical that it acts up when hot. If you can get the wheels off the ground, put the trans in park and get underneath and twist the drive shaft till it locks in park. You hear it click in. Although it may already be engaged depending on where the parking gear is positioned.
Take the throttle valve lever off.(top lever above shift lever) Then take the shift lever off. Drop the pan and take the valve body down. Pull it forward to pull the park rod out of parking pawl. Now you can change the solenoid and sensor easily.
Going back together is just the same. However sometimes it's tricky getting the park rod back in place. No tricks really. Just take your time.
Solenoid and sensor can be pricey. Probably should expect somewhere about $150 each.
There is also an upgrade available. I've never tried one but you can buy a billet aluminum block that installs on the vb and you can use a GM 4L80E EPC solenoid for the gov solenoid.