YODAONE

Pushing the horn button on 1999 LS400 did not produce an expected honking...

Not sure if humidity related but encountered a downpour hours before malfunction

However, tried the horn again the next day and it worked perfectly.

So it would appear there is an intermittent issue that merits attention.

Any members experience this issue?

How did you resolve it?... relay, wiring, connectors, actuator button contacts, grounding or ground wire?

Thanks.

dicer

Maybe its the takata air bag that's in the way, and leaking the propellant all over everything.

YODAONE

Have you encountered this as common or a primary cause of failure for the horn to honk?

dicer

No I was trying to be humorous. And more likely a clock spring deal, or the contact's like you mention.

sha4000

iTrader: (1)

I think it might be temperature related. Last winter when it was real cold my horn stopped working until the temperature raised back up some. Have you checked the connections by the hood latch?

Yamae

I'd distinguish which line is causing the problem measuring the voltages at the horn relay's pins.

Yamae

Attached is from a JDM service manual but it may be possible for English speaking people to find out where's the horn relay and the pin assignments. The pin#1 is connected the switch at the steering, pin#2 to the horn relay fuse and pin#3 to horns.

YODAONE

Please excuse but not familiar with "house latch"...

sha4000

iTrader: (1)

Fixed, hood latch.

YODAONE

Can you post a higher resulution image of the fusebox diagram. Thanks

YODAONE

Both horns have a single postive connector terminal and negative body grounding.

The horn and it's mounting tab is painted, the radiator surround is painted, as are the tapped holes, and the fasteners are again painted(?) thread-forming screws with lock washer and captive flat washer.
The attached images clearly show a deficient grounding scenario.

I am beginning to think such grounding issues are systemic.





Painted horn mounting bracket side that mates with painted radiator shroud to ground.<br/><br/>Single wire connector




Radiator shroud tapped hole...painted at factory.




Horn bracket mounting fastener does not suggest optimal grounding between horn and body

YODAONE

Solved the intermittent horn problem....

The clock spring was functioning

The relay was working properly..

I observed

he horn would only work when the telescopic steering mechanism was adjusted all the way in...and both ends of the concentric shafts were abutting up against each other.

So I reasoned the lubricant was insulating the sliding components...

A supplementary grounding cable was fabricated using more flexible 14 gauge fine strand tin-plated marine wire with a #8 and 3/8" ring terminal.

This ground strap was connected at the existing ground strap (closest to driver)#8 screw hole and routed alongside the steering column harness with a loop the loop(permitting extension and retraction) to the steering column support bolt(right of column)

The loop was affixed with a single small cable tie where finger is holding wire loop in image.


Supplementary ground wire installed. Finger is where mini cable tie was affixed.



To better access this ground screw, slightly bend downward the steering column harness support bracket. I left the original ground wire in place and simply added another at this location



This is where the 3/8" lug was affixed to the body...wire barrel side up serves as a stop to prevent spinning of the terminal whien torquing nut... Horn works better than ever.

dicer

Nice catch, I wonder if Lexus ever figured out to ground the upper steering column? So the normal ground is just through metal that slides?

YODAONE

The normal (original) ground wire spans across the tilt joint pivot and ends before the sliding mechanism...so before adding a ground wire from that point to the body, continuity was inconsistent. Now the horn works.