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Mike S.
Mike S., ASE Certified Technician
Category: Buick
Satisfied Customers: 7081
Experience:  A.S.E. certified
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On our 99 Buick Park Avenue, the negative to terminal #85

Customer Question

On our 99 Buick Park Avenue, the negative to terminal #85 fades to zero under the load of the operating coil of the starter enable relay
JA: Okay, I'll connect you to the mechanic to discuss this further with you. Before I do, is there anything else you want him to know?
Customer: This is relay #31
Submitted: 1 month ago.
Category: Buick
Expert:  Mike S. replied 1 month ago.

Hi, I am Mike, welcome. I'm reviewing your question.

Expert:  Mike S. replied 1 month ago.

It should. What are you trying to do?

Expert:  Mike S. replied 1 month ago.

Can I assume the starter doesn't crank over?

Check the "starter" fuse in the underhood junction block.

Expert:  Mike S. replied 1 month ago.

You had the voltmeter on the ground side of the relay, that is testing for a voltage drop and 0 volts is actually a good reading.

Expert:  Mike S. replied 1 month ago.

What are you trying to do?

Can I assume the starter doesn't crank over?

Expert:  Mike S. replied 1 month ago.

Here is the Starting Circuit,

Customer: replied 1 month ago.
That is correct. Starter does not crank. I made both available voltage and voltage drop tests on the entire cranking motor circuit. The ground to terminal#85 ofthe starter enable relay #31 fades to nothing under the load of the operating coil of the relay
Customer: replied 1 month ago.
Because this is rather technical, I prefer to do this by text rather than by phone.
Customer: replied 1 month ago.
I have positive, full battery voltage at terminal #86 and #87 under load. Not only are they working, this also proves the 2 fuses are good.
Expert:  Mike S. replied 1 month ago.

Does the relay click when you turn the key to start?

Expert:  Mike S. replied 1 month ago.

I don't know why you say #85 fades to nothing cause the pin #86 isn't supposed to have voltage until the key is on start. Pin #85 would not have any voltage either with the key off.

Expert:  Mike S. replied 1 month ago.

If the relay clicks, then install a new relay and try it again.

Expert:  Mike S. replied 1 month ago.

I'm getting ready to quit for tonite very soon so if you would still want help with this tonite, you have to answer my questions.

Expert:  Mike S. replied 1 month ago.

I got about 3-4 more minutes.

Customer: replied 1 month ago.
The relay does not click. All of the above tests were made with the key in the start position. There is no ground to the relay terminal #85
Expert:  Mike S. replied 1 month ago.

Ok, jump the 2 wires at the neutral safety switch and try it again,.

Expert:  Mike S. replied 1 month ago.

Unhook the transmission mode switch and jump the gray/white wire to the black/white wire and if the starter works then you need a new mode switch.

Customer: replied 1 month ago.
When I provide a new ground to terminal #85 the starter cranks indicating the relay, fuses, and starter are good
Expert:  Mike S. replied 1 month ago.

Yes, jump the tranny mode switch. Goodnite...

Expert:  Mike S. replied 1 month ago.

Did the starter crank with the tranny switch jumpered?

Customer: replied 1 month ago.
Pending, I am investigating your response.
Expert:  Mike S. replied 1 month ago.

ok

Customer: replied 1 month ago.
Patience sir patience
Expert:  Mike S. replied 1 month ago.

I cannot sit here and stare at the screen all day long. If you cannot give me a ballpark time when you might be testing it, then I might as well opt out.

Customer: replied 1 month ago.
You do not have to sit there and stare at the screen all day so. Walk away from the screen and get back to work like me. I'm sure we both have much to do. I am not even with the vehicle at this time. When I get back there I will perform those tests. I will get ahold of you. Patience
Expert:  Mike S. replied 1 month ago.

The thing is, I am done. That was the last test. If jumping the switch works, replace the switch. I would rather you just rate me now cause I am going on vacation now.

Customer: replied 1 month ago.
I can appreciate that sir. And I'm not trying to put you off. I'm at work right now. The car is at home. The job is not finished yet.
Expert:  Mike S. replied 1 month ago.

Just remember

Customer: replied 1 month ago.
It will be a few days before I get back to this. When I do I will contact you
Expert:  Mike S. replied 1 month ago.

This post is going to time out tomorrow at 9:02pm.

Customer: replied 1 month ago.
It's going to be a week or more until I have the time to look at the vehicle.
Customer: replied 1 month ago.
It is going to be a week or more until I have the time to get back to this vehicle. I will be in contact
Expert:  Mike S. replied 1 month ago.

whatever...

Customer: replied 1 month ago.
I had time to look at the circuit on the 1999 Buick, Park Avenue. There is no mode SW ( formerly referred to as the neutral safety switch ) in the normal location on top of the transaxle where the shift cable and actuating lever is. I purchased the neutral safety switch O'Riley Auto Parts lists. There is mounting bolt holes in the top of the transaxle where a switch could be ,however they were never used. There is no trace of a mode switch, no unplugged harness connectors. The last 8 of the VIN is x4641286 for your reference. This harness is virgin, and stock from the factory. Can you point out the location of the mode switch?
Customer: replied 1 month ago.
Further, the previous mechanic misunderstood me. The "Available Voltage" test at the negative terminal #85 of relay #31 fades to zero under the load of the operating coil. The "Voltage Drop" test results at this terminal shows a voltage drop of -12.6volts again under load, another point the previous mechanic misunderstood. The "Available Voltage" test is distinctly different than the "Voltage Drop" test.
Expert:  Mike S. replied 29 days ago.

I had already opted out because when you said it would be more than a week before you could get to the vehicle, after the already 7 days since this post was opened I felt it was not soon enough for me to continue, then I got an email from justanswer saying I was rude to you. I don't recall being rude but in case it appeared that I was I apologize.

I did respond to your mention of that pin #85 dropping to zero volts and I asked you dropping from what because there isn't supposed to be 12 volts on that circuit unless the key is turned to start. Nonetheless, I had narrowed it down to possibly the transaxle mode switch, then you came back saying it don't exist. If you would have looked at that wiring diagram more closely you would have noticed it said, "internal mode switch" and this is the explanation from the repair manual,"The Internal Mode Switch (IMS) is a sliding contact switch attached to the selector detent inside transaxle side cover. See Figure . The IMS replaces the Park/Neutral Position (PNP) switch, which is used on all other models. IMS communicates switch position information to PCM, that is used for engine controls and for determining transaxle shift patterns."

Here it is #9 In this diagram.

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