Key Sense, When is it Needed?

Printed From: the12volt.com
Forum Name: Car Security and Convenience
Forum Discription: Car Alarms, Keyless Entries, Remote Starters, Immobilizer Bypasses, Sensors, Door Locks, Window Modules, Heated Mirrors, Heated Seats, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=137768
Printed Date: May 01, 2024 at 6:39 PM

Topic: Key Sense, When is it Needed?

Posted By: shafferny
Subject: Key Sense, When is it Needed?
Date Posted: November 23, 2014 at 9:33 AM

When is/isn't the key sense connection needed and what purposes does it serve?

From what I understand, the key sense wire in the vehicle ignition harness is sometimes used to disarm the factory alarm system. In which case the key sense wire gets connected to the RS (-)status output, or an (+)ignition wire, depending on the polarity needed.

Other times the key sense wire is used as an RS/bypass input to deactivate a bypass so the vehicle doesn't see two keys at one time, which usually results in a situation where the vehicle remote starts, but can't be taken over by the key.

I've also noticed that some vehicles have a key sense wire in the vehicle ignition harness, but it's not imperative that it be connected. So how do you know when it's needed? If it's not needed for one of the above scenarios then you can just omit the connection?

(BTW, I'm posting this just for my understanding, not because I have an install specific question. posted_image

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Replies:

Posted By: dman007
Date Posted: November 30, 2014 at 10:21 PM

It is only needed if the car requires it in order to properly operate the remote starter. So you will know that you need it if:
1. It's posted on the forum by someone who has already worked on your particular car.
2. Some bypass install guides will instruct you to use it.
3. The remote starter doesn't act right ie sets off factory alarm or interior lights won't turn off.

As a safe bet, if a key sense wire is present I always hook it up. Sure it takes 1 additional connection. But I feel that it is always worth it to ensure that the remote starter works properly the first time without having to go back into your harnesses to then add another connection to the car.

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DTS Performance
St Petersburg, FL

Posted By: howie ll
Date Posted: December 01, 2014 at 10:30 AM

Also some Toyotas, Hondas where the remotes from the R/S don't unlock the vehicle during R/S.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Posted By: shafferny
Date Posted: December 01, 2014 at 2:32 PM

howie ll wrote:

Also some Toyotas, Hondas where the remotes from the R/S don't unlock the vehicle during R/S.

So do you have to kill the remote starter or just use the OEM fob to unlock the vehicle?

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Posted By: shafferny
Date Posted: December 01, 2014 at 2:38 PM

dman007 wrote:

As a safe bet, if a key sense wire is present I always hook it up. Sure it takes 1 additional connection. But I feel that it is always worth it to ensure that the remote starter works properly the first time without having to go back into your harnesses to then add another connection to the car.

That makes sense. The worst case scenario is that you didn't need it, but hooking it up won't hurt anything.

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Posted By: howie ll
Date Posted: December 01, 2014 at 4:19 PM

No, sometimes AFIK even the OEM remotes won't work during R/S unless the vehicle "believes" the key is in the ignition.
Did a Viper in a Yaris diesel a while back, connected what I thought was the second status to key switch, customer could only unlock doors with key during remote start, I'd actually connected WHITE/ blue not blue/white, DOH!
As soon as I corrected it, i.e. enabled key sense he could unlock with either OEM or Viper fobs during R/S.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Posted By: shafferny
Date Posted: December 01, 2014 at 5:22 PM

That's weird. It's something I'll have to keep in the back of my head for the future.

BTW, it's nice to know even a seasoned vet like yourself makes stupid mistakes. posted_image

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Posted By: howie ll
Date Posted: December 01, 2014 at 5:27 PM

All the bloody time lately, been in the game too long, it's winter and I was 200 miles from home!

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Posted By: howie ll
Date Posted: December 01, 2014 at 5:32 PM

Actually, making mistakes as long as they don't cost too much are all part of the learning curve, I've never achieved it but you can discipline yourself, test and double check. N.B. Apply that to a soldered joint to a Viper H2 wire by pulling on it and you'll break the wire!
Worst part of the Vipers which are remarkably trouble free?
The wiring looms, awful quality.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Posted By: shafferny
Date Posted: December 01, 2014 at 6:11 PM

Knock on wood, I haven't made any costly mistakes yet. Just some that I've had to troubleshoot and figure out where I went wrong. One thing I'm come to learn with electronics is that there isn't a lot of room for error. And when you do make an error, it can be VERY costly. For that reason I test, test, and test again before making a connection.

Getting back to your reference to Toyota's and Honda's. I read somewhere that with some of them the factory key fobs are rendered useless when the vehicle is running, remote started OR started with the key, is that true?

I recently installed a Compustar in my mother-in-law's 2012 Chevy Cruze(flip-key). I thought something wasn't right because the factory key fob wouldn't respond while the vehicle was remote started. After reading up on it, it turns out that it's pretty common among the newer GM flip-key vehicles.

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