04 LX470 AHC, brake controller, & Electrical Issues Question (1 Viewer)

[A2B in a TLC]

.....looking for an AHC & electrical guru for insight......I have an 04 LX470 w 106K miles on it. I had the AHC fluid changed recently and everything seemed fine.

I recently had a Tekonsha P3 brake controller installed using a Tundra (nothing listed for 100 or LX470 andmy research on MUD, etc indicated this route) pigtail wired into the factory trailer lighting/brakes harness under the dash and back to the factory trailer plug under the bumper. With this setup, I can charge my trailer battery while driving.

Issue number 1: When I shut off the motor (ignition off), the rear wiper comes on and cannot be turned off unless I disconnect the trailer battery using the battery box switch. Once I do this and the wipers stop, I can switch the battery back on with no wiper problem.

Issue number 2: On occasion, the rear wiper does not come on. However, this causes the VSC off and VSC Trac dash lights to come on. Once again, if I pull over shut off the ignition and turn the battery switch off, then restart, the VSC off and VSC Trac lights go out. Strange.

Issue number 3: It was after one of the VSC dash light episodes that my AHC began to act up. The rear has been high, or higher than the front by about 3". The low setting no longer works. Coincidence? Also, the AHC is very slow to react to H setting. In H, the rear does rise a bit. The front also comes up.

I did check all fuses, disconnect the battery to see if the ECU would reset.
I have pulled the rear and one front sensor. They are mint, no corrosion at all. I have also spent umpteen hours on MUD researching the problems.

So, is there`an electrical relationship between the apparent ground problem thru the trailer brakes to the rr wiper, the VSC off and trac fault, and AHC?

Thanking you for your input in advance.....

Bruce
A2B in a Toyota Land Cruiser

 

[agaisin]

might be worth checking for dtc trouble codes for ahc issue(s) and for vsc/trac issues. don't think an obd scan tool will be able to show you either but the fsm has steps to display them and there are threads here on the topic.

regarding the trailer harness modification and random vsc trac issues, here are three threads worth lookin at:
https://forum.ih8mud.com/100-series-cruisers/206121-vsc-off-while-towing.html

https://forum.ih8mud.com/100-series-cruisers/606885-rth-trans-vsc-abs-problems.html

https://forum.ih8mud.com/100-series-cruisers/359107-dtc-1330-vsc-off-vsc-trac-lights.html

regarding ahc issue - hard to believe they're related, but then again you can/should take a look at the electrical wiring diagrams to see if/where/how the systems may connect.

also - you checked all the fuses? ie the box in the engine bay, the box in driver side kick panel and the box in the passenger side kick panel?

Sent from my iPhone using IH8MUD

 

[jOnathN]

Art posted all the good info. I will only add a few extra thoughts:
1) The AHC problem is *probably* not related to the other wiring issues. I say that since the AHC symptoms you describe are common when the system ages. *However* the trailer wiring issue causes power feedback which could conceivably hash a bunch of things...not likely exactly, but possible.
2) re: the common AHC problem referenced above... You probably have a worn out rear sensor. They do not normally fail from corrosion since they are well sealed. They fail from friction wear - in the battle between tiny metal brush and carbon trace the metal brush wins. This is NOT casually visible but you can see the shiny wear marks if you take the sensor apart. 5 minute fix to replace the sensor and you'll be good for another 100k miles or so.

J

 

[A2B in a TLC]

Thanks for the replies, gents. Yes I did check all fuses, including the engine bay and behind driver's and passenger side kick panels.

When I pulled the rear AHC sensor, I cleaned up the tracks with a q-tip and some maf spray cleaner. I could see ridges as mentioned.

My issues occur following towing. My trailer only places about 300 lbs on the tongue, so not the biggest load. After towing, the rear is high and the front is REALLY low. It usually takes a while and several attempts at the high setting for things to normalize. BTW, I did adjust the torsion bars to lift the front about 1" just to relieve the load a touch.

I think my best decision now is to take her in to the Lexus dealer to pull the codes. If you are correct and its the rear sensor, I could easily replace myself or have them do it depending on price. I think the sensor is about $300 on eBay.

Thanks again,

Bruce
A2B in a TLC

 

[A2B in a TLC]

UPDATE:

AHC continued to occur periodically. The rear was OK but the front would drop to the rubber stoppers then rise again after a time. For now, I have pulled the AHC fuses and although the ride is soft, all is fine for now.

It turns out that my battery is low. A thought occurred: Will a low battery affect the AHC performance? The AHC must be a huge draw given the fuses, so a low battery might result in intermittent problems????

Bruce

 

[uHu]

.... BTW, I did adjust the torsion bars to lift the front about 1" just to relieve the load a touch.

UPDATE:
AHC continued to occur periodically. The rear was OK but the front would drop to the rubber stoppers then rise again after a time. For now, I have pulled the AHC fuses and although the ride is soft, all is fine for now....

Adjusting the torsion bars to achieve lift wil put zero pressure on the ahc, which is not good. But, if it drops to the rubber stops this can not be the case.
When it comes to ahc vehicles, you tighten the torsion bars to get the front ahc pressure right; and change the rear coils to get the rear pressure right.

I suggest getting the techstream kit and check the ahc pressures and sensor height readings. A faulty sensor (or wiring (unlikely)) or a maladjusted front sensor could give this symptom.
Checking these readings during ahc operation could reveal the secret.

 

[taco47001]

I realize I'm bumping a very old thread but I am having the same issues regarding funky electrical (rear wiper, and VSC/ track off lights) when I turn ignition off, only when my trailer is hooked up. If I pull 7 pin before killing engine...all is well. I have no AHC issues though.... Was there a resolution to this??

 

[txtortoise]

New trailer hookup or just started happening with previously stable setup?

Old post referenced the Prodigy P3, but sounded like a custom wiring job. If you truck has factory installed 7-pin and you're running a Prodigy P3, then might remove one variable by using their plug-n-play connectors.
Tekonsha Plug-In Wiring Adapter for Electric Brake Controllers - Toyota and Lexus Tekonsha Accessories and Parts 3040-P

I've used these on LX-450, LX-470 and LX-570 without issue...all my issues were on the trailer side wiring.

 

[taco47001]

New trailer hookup or just started happening with previously stable setup?

Old post referenced the Prodigy P3, but sounded like a custom wiring job. If you truck has factory installed 7-pin and you're running a Prodigy P3, then might remove one variable by using their plug-n-play connectors.
Tekonsha Plug-In Wiring Adapter for Electric Brake Controllers - Toyota and Lexus Tekonsha Accessories and Parts 3040-P

I've used these on LX-450, LX-470 and LX-570 without issue...all my issues were on the trailer side wiring.

New trailer hookup. I've towed a different trailer with no issues with the same setup. I own a 6x12 tandem with dual axle brakes but no battery, and I've recently purchased a travel trailer WITH a battery. The issue is with the new. I do have the prodigy 3 and I used the vehicle specific harness attached via connector buried inside the dash.

After a lot of research on here I went ahead and ordered the relay referenced in an earlier TSB with a PN-82241-60100. My LX470 does have the factory 7 pin.

 

[TXLX100]

It sounds like the trailer battery could be feeding the vehicle power. You might try searching harness setups with diode to ensure the current only flows from the vehicle to the trailer.

 

[taco47001]

Now to figure out where I have to install this "relay".....

 

[txtortoise]

Since the trailer hookup is new, is there a chance there's a mis-match or short in the trailer harness that occurs when you connect the 7-pins. Normally the truck is killing the connection when ignition is off. Can you hook your truck up to another travel trailer and see if the behavior is the same. That would significantly narrow down the issue to one or the other.

 

[TeCKis300]

I don't believe this is a harness issue. There were known feedback issues in some of the early gen hundies, that required a isolation relay.

 

[taco47001]

I bought the relay online last night, where do I install it?

 

[abarr]

I need to order that same relay for my 2003 LX470. Where did you order it from? Did you figure out how to install it?

 

[taco47001]

No I haven't figured it out. The only thing I find online says "installs inline wth factory tow wiring" but the connectors don't match to in between the main loom and the 7pin harness connector. I haven't spent much time on it though as the problem is resolved by just unplugging before I turn the truck off. Let me know if you come up with anything too.

 

[taco47001]

Hope this helps someone in the future

 

[Arya Ebrahimi]

Hope this helps someone in the future

It helped me! Just gotta see if I can find the relay at a dealer on the route of our current cross country road trip now!

 

[taco47001]

It helped me! Just gotta see if I can find the relay at a dealer on the route of our current cross country road trip now!

Awesome! I actually meant to update this post but I forgot. I have had zero electrical demons from back feed after installing this relay. It's solved my issues.

 

[SICARIO]

Awesome! I actually meant to update this post but I forgot. I have had zero electrical demons from back feed after installing this relay. It's solved my issues.

Thanks for the Pictures, very helpful. I have my relay on order and will install as soon as it gets here. Hoping to cast out the electrical demons in mine as well...