Constant 3rd Gear showing on DS

[dthrock]

I recently purchased Directscan and installed it into my GN. Right away I noticed that it showed in 3rd gear all the time. The car physically has no problems shifting and the 4th gear light comes on when it goes into 4th, but the 3rd gear stays on constantly.
Hmmm didnt clean the ecm connector enough. Took it out, cleaned it till I was afraid to take the pads off of the connector. Still the same story. I intended to buy an extra ECM in any case so I did that and decided to try that out as well. Exact same indications, 3rd gear on all the time. I talked to Bob at BM Computers and he suggested I post it here as he didnt think it was a problem with DirectScan at this point.
To make sure all the data is there:
Swapped out ECM's but used the same ribbon cable, parallel cable and DS box. I looked at all connectors on the cables and couldnt find any problem with them (nothing bent, gooped up etc)

Could it possibly be a bad signal from the transmission wiring to the ecm/DS? It doesnt seem to effect performance but it concerns me that the ecm is getting a signal all the time that says its in 3rd gear.


David

 

[MeanBuicks]

The 200-4R pressure switches are normally closed; ie. grounded. If your 3rd gear indicator is always on, you either have a bad pressure switch, disconnected wire or no pressure switch at all.

Is your transmission an original BRF unit? If not, it most likely does not have the 3rd gear pressure switch & wire.

If your transmission is the correct model, you'll have to pull your pan to investigate further.

 

[dthrock]

It is a BRF unit that we put in it about 3 months ago, rebuilt. Before that some idiot had a caprice tranny in it.
Will this cause any issues like it is other than bugging me when I look at Directscan?

David

 

[MeanBuicks]

No.

 

[WE4]

Greg's on it

Greg was right , I think..hehe.
Ck the switches in the trans specifically the one pointing to the rear. This is the 3rd gear switch. If switch was shorted to ground it would show on DS that it was on all the time even in park. Good Luck and if you need a switch lemme know

 

[MeanBuicks]

Uh, wait. The pressure switches are normally closed, which means they are always shorted to ground. They open when pressurized.

Therefore, if the circuit was open all the time because of a missing switch or disconnected wire, the ECM would percieve that as 3rd gear on all the time. If there was a pinched wire causing another path to ground, the ECM would never register 3rd gear apply.

 

[dthrock]

Originally posted by MeanBuicks
Uh, wait. The pressure switches are normally closed, which means they are always shorted to ground. They open when pressurized.

Therefore, if the circuit was open all the time because of a missing switch or disconnected wire, the ECM would percieve that as 3rd gear on all the time. If there was a pinched wire causing another path to ground, the ECM would never register 3rd gear apply.

What type switches are these? Im assuming that applying ground is making the circuit and closing the switch? If this were true then when there was no power to the circuit the switch would open. Or more likely there is no voltage to the switch and its spring loaded or something. When pressurized the switch is forced open (or closed, depending on your point of view), making a contact that sends a signal to the ecm telling it (the switch) is closed. If that were true then it sounds like the switch is stuck open or the contact is being made all the time.
Hmm after reading this again it actually sounds like the ecm is using an inverted signal. If you remove the cable completely ie no voltage/signal at all both 3rd and 4th gear will come on, SO it must be using the switch to turn off the signal to the ecm until its forced open and loses voltage giving the ecm a 3rd or 4th gear reading. Of course there could be somethng else between the cable and the ecm once it leaves the tranny case that I dont know about.
Is any of this even close to how it works? Forgive me Ive never seen the inside of one of these things.

 

[dthrock]

doh

Ah ah the light turns on. The switch is normally closed completing the the circuit to the ecm. When pressure forces the switch open it breaks the circuit telling the ecm that the car is in 3rd or 4th gear. All of which explains why when the cable is removed both 3rd and 4th gear come on and also what Greg was saying about the wires being grounded never letting the ecm know it was in 3rd gear.

Of course all of that is what Greg said, it just took me a bit to work thru the thing.

Having been enlightened now to the whole thing, which wire should I look at for breaks (easier than pulling the pan) to start with, or should I even bother with it and just wait till next time I have the pan off to check it?

David

 

[WE4]

Yes...

That is right, hey i answered that in the middle of the night and I have WAYYYYYYY too much crap on my mind. Thanks Greg and yes he is correct.

 

[turbojimmy]

So what if 3rd gear never shows "ON"? 4th shows on, but never 3rd. Is it the same switch?

I ask 'cause I hacked into the ECM wire for the BstC...wondering if I messed it up.

TIA,
Jim

 

[MeanBuicks]

No, there are separate switches for 3rd and 4th gears. If yours nevers shows 'on', you either have a bum switch or a pinched/chafed 3rd-gear switch wire shorted to ground.

 

[turbojimmy]

Thanks for the reply....I'll have to check it out. I was reviewing TLink runs from earlier in the month (pre BstC) and it was showing up. Now it's not. I might've severed the wire with the BSTC install?

Jim

 

[dthrock]

Update

OK had the car up on the lift yesterday (getting the pesky oil leak fixed from the front and back mains) and took a look at the cable that plugs into the tranny. The 'ear' piece that snaps onto the hook is missing. I was able to pull the plug right out with no force. Im guessing its just making contact on some of the connectors but not on the 3rd gear one.

So I guess the next question is how do I fix that broken clip? Duct Tape?

David