Trying to track down code E024

[Ronnie]

I've been bothered by a pesky code E024 (speed sensor circuit) when I have to sit for a long time stopped at a red light.  I think it is caused by a sticking 4th gear indicator switch inside the transmission telling the ECM the car is still in forth gear when the speedometer is reading 0 MPH. First thing I did this morning before leaving home for a long drive was add about a half a can of Seafoam Transtune to my transmission hoping it will free up a stuck 4th gear switch. 

 

EDIT: After about 125 miles of driving today I didn't get a code 24. I'm hoping the Seafoam might have fixed the problem.

[Ronnie]

Well the Seafoam hasn't cured the  problem.  Driving this evening I got a warning on the CRT telling me there was an engine problem. Checked diagnostics after I got home and I had a code 24 in history. AND... the 4th gear indicator in diagnostics was illuminated while the car was sitting in the garage.  The good news is the car is running and shifting fine.

[2seater]

I can't think of much that should be affected by a stuck switch other than it may allow the torque converter to lockup in a lower gear than normal, although if the chip programming is similar to 1990, there is also a minimum speed required. It could also possibly affect the EGR program but I would think that would be minor if at all.

[Ronnie]

If I put the gear selector in D, (3rd gear) the torque converter will lock up. Is that normal?  I need to follow the troubleshooting flow chart in the FSM to determine for sure if the code 24 is caused by the switches in the transmission. It's possible I could have a bad connection in the wiring or a bad ECM.

[DAVES89]

Ronnie, that is how I drive my car when the "Nascar" drivers are out during rush hour. The torque converter is then locked up for better acceleration.

[2seater]

1 hour ago, Ronnie said:

If I put the gear selector in D, (3rd gear) the torque converter will lock up. Is that normal?  I need to follow the troubleshooting flow chart in the FSM to determine for sure if the code 24 is caused by the switches in the transmission. It's possible I could have a bad connection in the wiring or a bad ECM.

As far as I know, lockup in 3rd gear is normal if all the other requirements are correct. As a matter of fact, I remember some GM models may also enable lockup in 2nd gear, all designed to improve mileage. 

[Ronnie]

Thanks for the info guys. Good to know that converter locking in 3rd is normal.   I just printed off the pages of the FSM with flow chart for testing the switches. If the garage isn't already too hot I'm going to do some testing now. If it's too hot I will do it early tomorrow morning. I'll let you know what I find out.

[Ronnie]

After some testing I have determined that the 4th gear indicator switch inside the transmission should be a normally closed switch and mine is either stuck open or the contacts are dirty. The 2nd, 3rd and 4th gear indicator switches should provide a ground signal to the ECM when the car isn't moving. My 4th gear indicator switch doesn't do that so the ECM illuminates the 4th gear indicator light on the CRT when in diagnostics. The code E024 is triggered when sitting at a red light for an extended period because the ECM sees the transmission in 4th gear and the speed sensor reading 0 MPH. The real problem here is the ECM is just to damn smart! ?

 

I think I have came up with a solution (or compromise) to prevent the code E024 and the warning message flashing on the IPC and CRT at red lights.  Only time will tell for sure if it's going to work.  While testing I discovered that if I ground pin B in the electrical connector that goes into the transmission the 4th gear indicator light goes out in diagnostics and the ECM is happy while the car is sitting still at a red light - without getting a code 24 or error messages on the CRT as I was before. 

 

Now, here is the compromise.  With pin B (4th gear switch) grounded I can idle as long as I want at a red light without problems but when I come back home and check for codes I have codes E028, 29 and 31 in history. That is because the ECM only sees the transmission go up to 3rd gear and never shifts into 4th and it thinks something is wrong because the speed and RPM don't match for 4th gear.  Again, the ECM is too damn smart!!! The good news is those codes didn't pop up a warning on the CRT  like the code E024 does and none of those codes appear to make a difference in the performance of the engine or the way the transmission shifts.  Maybe more driving will prove me wrong on that.

[DAVES89]

That's a compromise I could live with. I would much prefer a code that doesn't flash on the CRT scaring anyone driving [or riding] in the car.

 You should break this issue out and make it be it's own topic for someone wanting to do a search. It might be easier to find.

[Ronnie]

I'm still hoping the Seafoam Transtune will get the switch loosened up and working again. I added the ground wire to the 4th gear switch circuit in a way that I didn't have to cut or damage any wires and it can be easily removed at any time. If the compromise works out so I can drive the rest of this year I will think about trying to replace the switch over the winter but it looks like getting the side pan off would be a lot of work.  Maybe too much work just to replace a defective switch that doesn't seem to be making a difference in my ability to drive the car.

[DAVES89]

I could be wrong as I have never tried but I have read more then once that pulling the side cover entails pulling the transmission. Hopefully you can prove me wrong.

[Ronnie]

8 minutes ago, DAVES89 said:

I could be wrong as I have never tried but I have read more then once that pulling the side cover entails pulling the transmission. Hopefully you can prove me wrong.

I have that in the back of my mind too.  I don't think it's worth going to all that trouble unless I'm going to rebuild  or replace the transmission.  I'm getting too old to take on those big jobs just for the fun of it.