What controls the shift light?

[Hrtbeat1]

Does anyone know where the signal for the shift light comes from? I'm refering to the idiot light along the edge of the display. This is for a '90 auto but I'm sure others are the same.

I recently replaced the D36 rear with 2.59 gears with a D44 with 3.45 gears. I swapped the VSS with one calibrated for the new gears. The speed reads correctly (from what I can tell.) The problem is going down the interstate at 75 mph in OD my shift light comes on :confused I know I'm in OD because I shifted it through all the gears and felt it shift. The car is wanting me to shift again ..... to what, there are no more gears to go to.

I haven't checked the switches in the ECM chip yet. If its there I can change it. I was thinking it may be controlled from the CCM, which I can't reprogram. I guess my alternative is to remove the light bulb itself from behind the display.

Thanks for any input.

 

[Vettefan87]

I would guess the ECM, but that is my guess. I think mine goes on, if I have it in a lower gear and am driving around in Drive, instead of OD. I bet it is something to do with the RPM's of the engine being higher. With the ECM being used to the lower gearing, with the engine producing lower RPM's. That is my guess, good luck tracking this down. I want to do a gear swap too, but cant afford it right now ad.

 

[OLDCHEV]

I also have a 90 auto and have never seen any sort of shift light come on. Where is it located?

 

[redvett]

Its programmed in the prom. You either have to take out the bulb or get a custom prom.

 

[Hrtbeat1]

Left of the tach, second little window up, first idiot light. Just above the 2 on the tach.

 

[Vettefan87]

Its programmed in the prom. You either have to take out the bulb or get a custom prom.

Yeah, that is what I was trying to say. You will probably have to get a different program in for the severe jump in gearing, or take out the bulb, or just deal with the light I suppose.

 

[Hrtbeat1]

Well I looked through all the variables on the chip and can't find anything that would even resemble RPM and shift points. I'm thinking it may be part of the CCM. It does the computing for the dash display, the MPG, Range, AVG, ect. from what I can gather.

 

[Hrtbeat1]

Memcal / Netres

:duh :duh :duh :duh

I don't know why I didn't think of this before. Its got to be part of the Network Resistor pack on the Memcal. This controls things like limp home mode, ESC, Knock sensor, and guess what REAR END RATIO.

I calld my local GM dealer and they couldn't find the proper one for a 3.45 rear. The guy did say he had about 6 listed. Some had ratios listed others didn't.

Does anyone have a broadcast code (four letter code on the Memcal) for a '90 Manual tranny with a 3.45 rear? I had a lot of this stuff researched but have misplaced my information. I also had a PDF file that had all the C4-C5 parts breakdown but somehow it got corrupted and has nothing in it anymore.

 

[G Winter]

Ok I have a 90 with the six speed and I think the 3.45 rear end . Is what your looking for on the car ? If I have a clue I could try taking a look.

 

[Hrtbeat1]

Man you are a life saver. :BOW This is driving me batty, but I've been doing my research and I didn't think they exist. If you could look at your Memcal there should be a four letter code on either the chip (inside the blue cover), or on top of the blue cover.

There are three 10mm nuts/screws that hold the ECM to the bracket. One toward the front, one toward the engine, remove these. The other is under the support brace you just have to loosen this one. The ECM should pull right out. There may or maynot be a cover for the wires to the back. On the bottom of the ECM there is a panel with four 1/4" screws, remove these and the Memcal is sitting right there.

If you could tell me the four letter code on it I would be forever greatful. From the research I've done I bet it will be "ARFP"

 

[G Winter]

ok I will do that tomorrow afternoon after work . To close to bedtime to do it now. I will get back to you tomorrow evening .

 

[Hrtbeat1]

Thanks so much. I may have the nut sequence backwards, but its really easy. I know you don't have to take all of them off.

 

[G Winter]

Hrtbeat1 I got what I think you are after. On the face (plastic cover) it has Delco APFP 7185 inside of a hole int the plastic it has Delco R605

I noticed you said you have an auto... wouldn't that be diff.. I have a 1 to 4 shiftlight.

 

[Hrtbeat1]

Hrtbeat1 I got what I think you are after. On the face (plastic cover) it has Delco APFP 7185 inside of a hole int the plastic it has Delco R605

Thanks so much. Now I know which ones to order from the dealer. Either one I have to modify so I can put my 'tuned" chip on it. I have to get one for an auto 3.07 rear (close as I can get) and one like yours.

I thought about the differences in the shift lights. Guess I'll just have to experiment.

Thanks again,

Gerald

 

[G Winter]

Your welcome. Was no problem took less than 5 min. Good luck.