viper 791xv stumped after diagnosing

I have a Viper 791xv installed into a Honda. Just had an issue with it after 4 years of no problems the other day.

I armed it, worked as normal, next day I went to unarm it, remote was not responding. I figured, dead battery (happens to the best of us lol), charged battery fully in car, still not responding, odd I thought, so I try my 2nd 2way remote. Same issue. Alarm not responding. Car turns on and runs just fine, however alarm is completely unresponsive.

Now, I am a computer engineer, so I know how to diagnose issues so tried my best at figuring out what was causing the issue with this alarm.

The LED (I never had one hooked up prior as I don't like the look of them and also believe it leads a potential thief to where your brain is) is not blinking. I hooked a spare up to my unit and it does not blink at all.

I figured that a possible issue is that the brain lost the programming for the remotes that is saved in flash memory. So I tried to reprogram. Left drivers door open, hit valet once, then second later held down until I heard tone (awesome I thought). I hit unlock on my remote. Unresponsive. :/

So next, I just so happened to have a 1 way DEI antenna from an older vehicle around that was known good last time I had used it, it is 3 wires, instead of 4 (missing the blue), however I assume the blue is for outbound communication versus inbound like this 1 way alarm had. I hook up this antenna, try the same steps. Still nothing.

I also checked all the fuses setup for this alarm, 5 in total I believe? None are broken.


From what I can assume, the alarm brain is broken, unless using a 1 way antenna on a 2 way alarm does not work, then it could be the antenna which is broken.

Please share your knowledge, I have known about this forum for quite some time and actually browsed it years ago when I picked out my alarm based off of some of the incredible experts here. Thank you so much for any help or diaging tips you can share with me to help further with my odd issue.

Have you tried the 2-way antenna again? Sometimes those units lock up and unplugging the antenna for a minute will get it to work again. Different antennas and remotes work off different frequencies so there is a good chance the 1-way antenna you tried would not work with the 791 remotes.

Try to unplug the brain, & put a long screwdriver against the contacts on the main harness, make sure all contacts are touching the screwdriver. Now move it back & forth across the terminals, this will empty all internal capacitors, now plug in your original antenna, & reprogram your remote, If that does not work, then I suggest you take it to a professional installation shop, where they have the resources to troubleshoot any problem w/ your alarm. Please let me Know if that works.

I will give it a try, since Viper's site seems to be flakey right now and not loading pages. Steps to setup new remote are as I was trying correct?

"So I tried to reprogram. Left drivers door open, hit valet once, then second later held down until I heard tone, hit unlock"

you shouldnt need to reprogram the remotes....  try unplugging the antenna for a few minutes.... it is an active antenna and this will "re-synch" it with the brain.... ( just like re-synching a modem)

i had my old 791 do this a couple of times....

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Kevin Gerry
Certified Electronics Technician
MECP First Class Installer

Owner/Installer
Classic Car Audio
since 1979

kgerry wrote:

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you shouldnt need to reprogram the remotes....  try unplugging the antenna for a few minutes.... it is an active antenna and this will "re-synch" it with the brain.... ( just like re-synching a modem)

i had my old 791 do this a couple of times....

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Awesome, will give that a whirl. I was just surprised as I had no issues since it was originally installed way back when. I am familiar with electronics, however I was assuming the antenna on an alarm is somewhat like a cellphone, no internals, just wired to the board and has no internal electronics except for the wiring itself to expand the signal reception from the brain itself. It sounds like from what you are saying is that they are more advanced than that, more advanced than maybe a cellphone or laptop wireless antenna where it is nothing more than just a wire to expand reception from the mainboard.

I will try this, along with powercycling the entire unit with leaving it unplugged for a while. I will post the results so I can help other users who have the same issue if I end up getting this fixed.

That is defitnely the first time i have heard someone not want to use the L.E.D because of making it easier to find the brain....I kinda understand...But i think it works wayyy more as a visual deterent ...then as a map tp your brain...I guess if you took the time to hide everything...maybe...But for the most part...you are kinda  shorting yourself....You could just extend the wires...run them all over the place if your really that worried...But the LED is a vital piece to the alarm system ...especially for the newb thieves...just my 2 cents...This would stop them from breaking your window...then realizing there is an alarm...!

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M.E.C.P & First-Class
Go slow and drink lots of water...Procrastinators' Unite...Tomorrow!

Been thinking about this and I agree with Tommy 100% nice flashing blue light at night great. Was once in a car park in Central London, the only two cars touched were my mate's and mine, neither had alarms. Think about that. The pro thief will always walk away from a car that has  non standard  security.