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A Mechanic's Life - Tales From Under the Hood

3515 messages,  Last post on Jun 18, 2013 at 2:06 PM

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     This topic is primarily for professional mechanics, current or retired, or ardent amateurs who would like to share the suprises, victories, tricks and challenges of working on the modern automobile. All Forums members are invited, of course, to ask technicians about their work, or comment on your own experiences dealing with mechanics.
 
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Messages Page 104 of 353

#1024 of 3515 Re: Here's a good one [explorerx4] by Stever@Edmunds HOST

Jan 29, 2013 (7:45 pm)

Replying to: explorerx4 (Jan 29, 2013 7:24 pm)
Great, when I get a new car, I'll have to take some tinfoil off my hat and wrap it around the fob.

#1025 of 3515 Re: Here's a good one [thecardoc3] by srs_49

Jan 30, 2013 (5:20 am)

Replying to: thecardoc3 (Jan 29, 2013 6:55 pm)
Any idea how to even start the diagnostics?
 
1. Do the door locks work with the key FOB?
2. Are these all factory installed remote start systems, or are some/all of them after market add ons?

#1026 of 3515 Re: Here's a good one [srs_49] by Stever@Edmunds HOST

Jan 30, 2013 (6:15 am)

Replying to: srs_49 (Jan 30, 2013 5:20 am)
I'm wondering if the shopping carts or the aisles have some sort of built-in RFID tech to either track the carts when people steal them or to run digital ads in the cart as you push them down the aisle. Hm, maybe it's just the items in the cart that the store is trying to track with RFID transponders. Push button ignitions use RFID (really, a shorter range proximately card) to figure out that you are approaching your car.

#1027 of 3515 Re: Here's a good one [steve_] by thecardoc3

Jan 30, 2013 (6:53 am)

Replying to: Stever@Edmunds (Jan 29, 2013 7:45 pm)
Now that's funny..

#1028 of 3515 Re: Here's a good one [srs_49] by thecardoc3

Jan 30, 2013 (6:55 am)

Replying to: srs_49 (Jan 30, 2013 5:20 am)
1. Do the door locks work with the key FOB?
 
No, in fact a lot of the people can't get into their cars at all.
 
2. Are these all factory installed remote start systems, or are some/all of them after market add ons
 
Factory systems.

#1029 of 3515 Re: Here's a good one [steve_] by thecardoc3

Jan 30, 2013 (6:57 am)

Replying to: Stever@Edmunds (Jan 30, 2013 6:15 am)
I'm wondering if the shopping carts or the aisles have some sort of built-in RFID tech to either track the carts when people steal them or to run digital ads in the cart as you push them down the aisle.
 
Good thought, now how would you "prove it"? Then, how do you fix it if that is the case?

#1030 of 3515 Re: Here's a good one [thecardoc3] by Stever@Edmunds HOST

Jan 30, 2013 (7:01 am)

Replying to: thecardoc3 (Jan 30, 2013 6:57 am)
If the frequencies are the same (or the store transponder is stepping on the one the cars use), you could dial back the power or move the transponder so the signal's not bleeding out into the parking lot.

#1031 of 3515 Re: Here's a good one [thecardoc3] by stickguy

Jan 30, 2013 (8:10 am)

Replying to: thecardoc3 (Jan 30, 2013 6:57 am)
it sounds like there is enough evidence now that the location is causing the problem. So you have 2 ways to go about diagnosing. 1 is try to get the car to tell you (though I would not be surprised if there was nothing to tell, since the car would think the fob was not there).
 
so, like Steve said, you almost have to work from the other direction. When you have an active failure, systematically remove a possible source of interference, 1 at a time, until the fob works..
 
if you can do that, maybe then you can reverse engineer a solution!

#1032 of 3515 Re: Here's a good one [thecardoc3] by busiris

Jan 30, 2013 (10:01 am)

Replying to: thecardoc3 (Jan 30, 2013 6:57 am)
About 10 years ago I was riding a Harley through the Alps. At the top of a pass we stopped in a small tavern (every pass in the Alps has a small eatery/tavern I think) that also had a large antenna array located behind it.
 
Before we left, the waiter told us if we couldn't start our bikes, just roll them down the road a couple hundred meters and try again.
 
Sure enough, he was right. We couldn't disarm the ignition lock via the key fob, but on a Harley, it can be done manually by entering a code through the blinker switches. One guy with us tried that and was able to start his bike before moving it. The rest of us just followed the waiter's suggestion.
 
I have no idea what the antenna array was for or what it was transmitting.

#1033 of 3515 Re: Here's a good one [busiris] by srs_49

Jan 30, 2013 (10:46 am)

Replying to: busiris (Jan 30, 2013 10:01 am)
An antenna does not have to be transmitting on the same frequency as the key FOB to perhaps cause a problem. For example, assume the key FOB works at (say) 400 MHz, and a nearby cell tower works at 2.2 GHz, 5.5 times higher than the key FOB. Even if the receiver in the car has a filter at the front end that is only supposed to allow the key FOB's frequency in, those filters are not perfect. So some energy from the cell tower can make it's way to the receiver in the car. This could overload the receiver (saturate the front end) so that it does not "hear" the key FOB signal. This is sort of like trying to pick out one voice in a crowd.
 
Another phenomenom that can occur is rectification. The cell tower's signal couples onto wiring or the key FOB receiver's antenna. It is then rectified (converted to direct current, DC) and the resultant DC bias can overwelm the front end of the receiver.
 
Either case can be fixed simply by moving the vehicle out of range of the cell tower.

Messages Page 104 of 353

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