Shift sensor issue and maybe something else?

[SHC286]

1998 k1500, 5.7/4l60e, transmission is about two years old.

My truck has a bad shift sensor. The way it was explained to me is that this sensor Is what tells the TC to lock at cruising speed? I have no idea wtf, I’m not a mechanic, I’m a half assed part swapper at best and I’m damn sure not a transmission guy. I’m good with tires and oil.

So the effect is, at around 50-55 mph it feels like it keeps wanting to drop out of that extra “Half gear” at overdrive. Again, this is how it was explained to me and I’ve noticed this effect, it’s impossible to miss.

By the way, has a code for bad shift sensor, so that part isn’t speculation or miscommunication.

I just went to town for a pack of smokes and it won’t go into 4th at all now and revs high as it goes into 3rd. Thankfully that trip is about two miles so I just cruised along at 40 mph cussing the whole way. Yesterday I put about a hundred miles on it and it didn’t miss a beat, didn’t even have that effect of dropping out of OD.

Was already planning to put my truck in the shop for a new steering section and to get that sensor replaced.

So my question is, could I be lucky and a new sensor might fix this, or do y’all think my transmission just took a big old steaming ****?
Checked the fluid level and it checked out fine, looks nice and clean too.

 

[SHC286]

Just read one of the stickies, and this seems like the limp mode mentioned. Sorry for not reading that first, I didn’t see it. Still interested in opinions though.

 

[Supercharged111]

The brake switch can keep you out of lockup.

 

[SHC286]

I’ll look into that once I address the rest of this problem and get 1st and 4th back.

 

[Erin]

When mine revved up between 2-3 gear it was a sensor. Can’t remember if the guy told me it was speed or shift sensor. I’m no mechanic or expert on part names by any means. I do know it was in drivers side of the transmission.

 

[Erin]

Sorry, on drivers side.

 

[thegawd]

theres 2 sensors. one is the TPS, throttle position sensor, it can be tested with a good obd2 scanner if obd2 equipped or with a multimeter. the other is the VSS, vehicle speed sensor on the transmission or tcase, I wouldnt know how to test this but I would think you should have a check engine light with a code. the tps can fail and not set a code because it just sends incorrect data and the ecm just believes it....

so it's a 98, plug in obd2 scanner, go to diagnostics, go to tps test and run it. it should show a graph and it should gradually rise up to 100% as you step on the throttle without any jumps or breaks in the line of the graph. replacing the tps is simple and it only cost $30-$40 but test it first. the truck dosent need to be running just ignition on to run.

Limp mode.... iv been there too. my burb had a failed ignition switch that was intermittent and a massive pain in the ass. limp mode is 3rd gear only, so you start in 3rd and continue in 3rd BUT you can manually shift from 1st or 2nd to get going and then shift to 3rd. You will also not have a speedo and your gear selector indicator will not be lit up.

limp mode can be caused by a blown prndl fuse (which could be cause by a shorted O2 sensor because the heater circuit uses the same wire as the tranny.) A disconnected transmission plug, the big round one behind the heat shield, just take the heat shield off to get it out of your way. A faulty ignition switch or a break in the pink wire that supplies Pin E with 12V+ to the tranny. Pin E should read the exact same voltage as the battery, if it's not the ecm will put the tranny in limp mode. carbon will build up on the contacts inside the ignition switch causing the tranny to be thrown in limp mode. it's a pain in the ass.

good luck.

Al

 

[SHC286]

Good info, thank you.

 

[Schurkey]

1998 k1500, 5.7/4l60e, transmission is about two years old.

My truck has a bad shift sensor. The way it was explained to me is that this sensor Is what tells the TC to lock at cruising speed?

No such thing as a "shift sensor".

By the way, has a code for bad shift sensor, so that part isn’t speculation or miscommunication.

WHAT IS THE CODE?

So the effect is, at around 50-55 mph it feels like it keeps wanting to drop out of that extra “Half gear” at overdrive. Again, this is how it was explained to me and I’ve noticed this effect, it’s impossible to miss.

That sounds like the Torque Converter Clutch isn't working properly. Possibly a TCC solenoid problem, or the wire harness to the TCC solenoid.

I just went to town for a pack of smokes and it won’t go into 4th at all now and revs high as it goes into 3rd.

Flare into 3rd makes me suspect the 3--4 clutch pack. Lack of 4th could be related to a problem in the 4th-gear part of the 2--4 servo.

So my question is, could I be lucky and a new sensor might fix this, or do y’all think my transmission just took a big old steaming ****?
Checked the fluid level and it checked out fine, looks nice and clean too.

A "shift sensor" will not fix this, because there isn't one.

A TCC solenoid, and/or a "shift solenoid" or two might fix this, although it could be a wire-harness problem to the solenoid(s). Might also be a failed 3--4 clutch pack or 2--4 servo. I'd expect dark fluid with a failed clutch, though.

 

[SHC286]

Well whatever the hell they’re called, the code reader said “shift sensor”. I’ll be sure to scold it for making up part names the next time I see it. I didn’t write down the number that came up with it.

I bought a full kit that should replace all the electronics and/or pressure operated doodads and geegaws including the harness and decided to get a new filter because why not? Gotta take the pan off and change all the fluid anyway, so might as well.

When I crawled under the truck I discovered my timing cover had apparently been leaking too. Oil level was good, so it’s not enough to drain it down between oil changes, but enough to piss me off and decided to take it to someone who works on trucks for a living.