99 4Runner Power Antenna

I am having a problem with my power antenna. A while back the mast stopped going up and down and was stuck in the “up” position”. After some checking I figured it was the mast that was broke and I found a new one on eBay for $18. I installed this new mast pretty easily according to the Haynes manual. The problem is that when the antenna goes to extend it appears that the motor doesn’t know when to shut off so even though it is fully extended the motor keeps trying to push it up more and you can hear the teeth grinding until the motor “times-out” and stops. It retracts just fine and stops when it hits the bottom.

My guess is that the motor isn’t getting the “signal” to stop extending the antenna. So my question is does anyone know what tells the motor to stop extending the antenna? Is it a mechanical clutch thing? Or is it merely timing?

Any input would be greatly appreciated.

Thanks,


Jim

Check the "sticky" posts at the top of this forum for the schematic for your truck or even a year that is close to see if there is a limit switch for the extended stop.
Here is the link for the service manuals at the top of this forum:
http://www.automotiveforums.com/vbulletin/showthread.php?t=510646

Well here is what I found out:

I found some schematics on the web as well as some of the ones listed above (Thank you! BTW). None of these diagrams shows an upper or lower limit switch. Only that the antenna up/down signals come from the radio to an antenna control relay. One circuit diagram that I found shows a partial circuit detail of the antenna and the solid state relays to control the antenna motor. The theory that I came up with is that this antenna control relay likely shuts off the motor when excess current is detected. Meaning, when the mast travels and reaches either the upper or lower mechanical limit the motor “binds” and draws more current than “normal” (but far less than would blow the fuse, of course). This “tells” the relay to shut off the motor. This is my guess. If anyone knows exactly for sure how this system works please let me know.

Anyway, I removed the antenna and opened the case to see what I could find. Nothing looked whacky. I put it all back together and the same result the antenna would extend but the motor would continue to run and give a grinding sound until the relay timed out.

I decided to try and look at the antenna control relay. I found it but I didn’t actually pull it out of the car. I wiggled it and listened to see if it was turning on and off as an initial troubleshooting step. Sounded “ok”, it seemed.

I then took the antenna back out and decided to peek at the DC motor that actually runs the antenna up and down. I found that the brushes were worn down quite a bit. I found some equivalent replacements at a hobby shop and with some minor modifications replaced the brushes, reassembled the whole thing and tested it. It worked. However, I am unsure of exactly what fixed it. Maybe just the tear down, cleaning, an reassembly? Wiggling the control relay? Who knows?

But I have a decent working knowledge of the power antenna system…and a theory as to exactly how the mast knows when to stop going up and down...

Cheers,


Jim B.

Jim,
I am having the EXACT same problem. Could you tell me where the relay switch is located..
thanks,
mike