The New Life of the 3800 "Formula"

[TopNotch]

Since I have a new PRNDL swtich on the way anyway, I tried monkeying with the old one again to see if I could make it work. In the first picture, you can see what's inside the switch. There's supposed to be a rubber gasket in the depression around the outside of the metal part, which was FUBAR, so it's good that I'm getting a new switch. After my monkeying, it still doesn't work. The 2nd picture shows the codes I was getting. QDM 4 is also related to transmission electronics, and the new switch may clear that as well. I don't know what caused the Fuel Trim Lean.

[GTRS Fiero]

I hope that clears the QDM code.

[TopNotch]

Yesterday I got the new switch and put it in. There are still problems, but I will live with them for now, as they do not affect the drive-ability of the car. It seams that the switch positions do not exactly correspond with the transmission lever detente positions. in park, the transmission should indicate "neutral" to whatever circuit the scanner is reading. If you put the transmission in park, and then press slightly forward on the lever on the transmission with your fingers, it does indicate neutral on the scanner.
So I ordered a Helms manual for a 1995 Buick Park Avenue from Ebay. I will study the circuit, and perhaps add a momentary push button that is pressed by the lever on the transmission when in park, wired to give the proper indication.
Currently, the scanner indicates "4th" with the console shift lever set to Drive, "Neutral" in neutral, and if you pull the shift lever all the way backwards, it indicates "Low". I'm pretty sure that much is normal.

[Fierofool]

Just a minute difference in the fulcrum point of the lever or the location of the cable attachment to the lever can change the travel at the other end where the switch is located.  Even length of the cable can affect it. 

[GTRS Fiero]

My Fiero's shift lever does not quite match the detents to the gears.  Reverse is a bit off, as is Neutral.  It's difficult to get into first.  The other gears are good, though.

[GTRS Fiero]

Oh.  There is an adjustment on my switch.

[TopNotch]

Oh.  There is an adjustment on my switch.

If you mean the elonged mounting holes on the switch, they don't fix my problem, and 4th and neutral work best with the mount centered anyway.

[GTRS Fiero]

Mine has a marked hole on the switch to allow adjustment.

[GTRS Fiero]

I guess my article isn't published, yet, so here is what I found with a quick search.

https://www.fiero.nl/forum/Archives/Archive-000001/HTML/20160323-2-122706.html

[GTRS Fiero]

Did you get the QDM code resolved?

[TopNotch]

I thought I had read something previously that said QDM4 had something to do with the transmission, but it does not. QDM4 (Quad Driver Module 4) controls
1) the AC clutch relay (can't be that, because the AC works).
2) the low speed fan relay.
3) the high speed fan relay.
Since the car has no 2-speed fan, that could be the source of the problem. I will investigate when I get the manual.
All these outputs energize the appropriate relay by pulling to ground. The error is set if the voltage of any output is not what is expected (which should be near 12V if off, or near ground if on). So the fix may be as simple as adding a pull up resistor on whatever output is not used (for example, low speed fan).
BTW, the car has never overheated since I flushed the cooling system.

[GTRS Fiero]

I was thinking you could just make either fan trigger activate the same fan.

[TopNotch]

I was thinking you could just make either fan trigger activate the same fan.

That may not work. If the low speed signal is pulled down, and the computer is still monitoring the high speed signal, expecting it to remain high, it may trigger the QDM4 error.

[GTRS Fiero]

It shouldn't affect the high-speed signal.  The low-speed should have its own relay, and connect to the fan on its own.

[TopNotch]

It shouldn't affect the high-speed signal.  The low-speed should have its own relay, and connect to the fan on its own.

But for both signals to work the same relay, they would have to be connected together. So if the low speed signal activated (was pulled low), it would of necessity pull the high speed signal low also. The computer would see it go low when it hadn't commanded it to go low, and that could be an error condition. I supposed I could alleviate that with diodes and pull up resistors.