450H brake lights on permanently

Grey RX · February 2, 2019

My 2010 RX450H has the brake lights on permanently (even with engine off) plus amber brake system warning light on the dash. Anyone have an idea what this might be please?

I did try to find a fuse to remove to get the lights to go out but had no luck tracking one down. Any advice gratefully received.

Almost certainly unrelated but I think the car was the subject of a failed keyless theft last night. Someone left food wrappers at the front door, car drivers door and on the pavement behind the car. Fortunately our keys are well away from the front door.

Farqui · February 2, 2019

Check the switch at the top of the brake pedal?

Grey RX · February 2, 2019

Thanks for the suggestion. I went back out in the cold and ‘poked around’ with it a bit. No brake lights on now so at least I won’t have a flat Battery to deal with. Will see what tomorrow brings, assuming it’s still there. Removing the starter system fuses might slow up keyless thieves though.

Texas · February 2, 2019

Can you 'turn off' your remote keyfobs? Will be owners manual. On some you can stop the constant transmission of codes from the keyfob by a sequence of button pushes but it will turn back on the next time a button is pushed. might also be good idea to invest in a RFID shielding wallets for the fobs.

paul m.

Herbie · February 3, 2019

Or better still, get the Faraday pouches but also invest in a good steering lock because prevention is better than cure.

Have a look at this topic:

Grey RX · February 3, 2019

IMany thanks for your advice. I’ve discovered you don’t seem to be able to disable the key fobs themselves but you can disable smart entry and smart start on the vehicle by using the steering wheel controls to access the customisation menu. Slightly less convenient because you need to use the fob buttons to unlock the car and hold the fob up against the start button to start, but I think I’ll leave it disabled whilst there seems to be a gang of scumbags in the area and I decide what to do about a steering wheel lock.

Really helpful link thanks.

Herbie · February 3, 2019

Any news on the brake lights?

Grey RX · February 3, 2019

Lights now functioning normally after I prodded randomly at the brake light switch, working it on and off for a while. I guess it is on the way out so will get it changed when it is serviced in 2 weeks. I can’t really face changing it myself in this weather

Rich

Texas · February 3, 2019

If you have Cruise control then you might find that this plays up and malfunctions as the brake pedal switch is an intergral part in the cruise control system for obvious reasons.

Paul m.

Grey RX · February 4, 2021

An update on this plus another question. After two years of no repeat of the problem, returned to the car to find the brake lights permanently on again. I bought a new brake light switch from a nearby Toyota dealer - part no 84340-30110 for £37.00. For anyone looking to do the job then this link was very useful although the partno is wrong. It also skips over removing a black lower dash panel which contains the footwell light and the OBD port. Not at all easy to get to but not impossible. A stubby spanner is a must though.

https://www.clublexus.com/forums/rx-2nd-gen-2004-2009/841199-diy-rx-350-brake-switch-w-pictures.html

Having replaced the switch I tried to start the car only to find that the lights had been on long enough to drain the 12V Battery so the car threw a fit and multiple errors plus a CEL. I charged the Battery (discovering that the Battery well had about an inch of water in in the process). Reconnected and all well and good except after 5 mins of driving the Check Brake System and Check ABS messages came up with amber warning lights for both. I don't think the ABS is working either. Brakes have no problem stopping the car though.

I'll have to call the dealers tomorrow but wondered if anyone had any thoughts about what the problem might be - ie remortgage expensive. I'm wondering if the warning messages are left over from try to start with a flat Battery, I've caused a problem in changing the brake light switch or by some genuine coincidence the braking system (actuator, ABS or something) has actually failed at the same time.

ColinBarber · February 4, 2021

2 hours ago, Grey RX said:

I'm wondering if the warning messages are left over from try to start with a flat battery,

I would suspect this. Should have nothing to do with the brake pedal switch and coincidences very rarely happen.

Grey RX · February 5, 2021

Really appreciate your insight Colin. Tried the car again today before I spoke to the dealer. No error messages. Left running for 10 minutes, went on a ten mile drive. Still nothing so fingers crossed I might well have dodged a bullet.

Now I just have to work out where the inch of water in the Battery compartment is coming from which I only discovered when charging the Battery. Completely dried it out yesterday and some is back today after the rain last night.

If anyone is interested this is the part.

Grey RX · February 5, 2021

Oops. Spoke too soon. Started it again after a few hours - error messages back. Drove around a bit, stopped and started again and messages gone. Think I'll have to get a dealer to take a look - maybe the Toyota dealer less than a mile away can at least check it.

Herbie · February 5, 2021

1 minute ago, Grey RX said:

Oops. Spoke too soon. Started it again after a few hours - error messages back. Drove around a bit, stopped and started again and messages gone. Think I'll have to get a dealer to take a look - maybe the Toyota dealer less than a mile away can at least check it.

I don't know about Toyota but I do know that Lexus dealers charge about £135 + VAT for labour.

This is an electrical problem so why not just go to a decent auto electrician who'll charge about half that or less. Alternatively, try to narrow it down a bit further yourself by reading the OBD2 fault codes with Techstream.

Mutz99 · May 31, 2022

Did you ever get to the bottom of this issue?

I have the exact same problem - mechanic is telling me to order a new brake switch. Will this cure the 'check pcs system' and the rear brake lights staying on randomly?

Thanks in advance

Grey RX · June 30, 2022

Hi, Sorry I didn't see your post sooner. I replaced the brake switch as your mechanic was suggesting but it didn't help. Ended up going to the dealer who diagnosed a faulty relay (an expensive relay). It was replaced and has been fine ever since.

IAH123 · December 9, 2022

Having the same issue. Which relay was faulty? Thanks.

Grey RX · December 12, 2022

I must confess I don't know for sure. It was one behind the glovebox area somewhere. I'll dig out the dealer receipt when I get home and check. I know this is sacrilegious here but I messed around with it myself, tried a couple of local garages all to no avail. My best move was to take it to the dealers where it was fixed in one day.

December 28, 2022

I have the exact same issue with you right down to the water in the Battery compartment! There are two grommets when you remove the Battery tray which I took out and it seems like the water has stopped building up. I could not work out how it is getting in and I know this is not a great long term solution but seems to have cured the issue for the moment. I wonder if water touching off the cables there could have caused our brake light issues... :wacko:

If you are able to share any specific details on the relay it would be very much appreciated. Good to hear you got sorted, its a real pain

Grey RX · January 16, 2023

Finally tracked down my invoice for this. Sorry for delays but hopefully this will be useful for someone. The error message the dealer uncovered was C1380 Stop light really malfunction. The relay replaced was part number L895A0-30010. The dealer also describes having removed gloves and trims to gain access to the relay.

Sad to say my problem has returned. Since I have been getting a lot of misting of the front windscreen and it has been raining a lot more, my suspicion is that there is a leak which is getting onto the relay.

exomen · January 30, 2023

Got exactly the same issue. RX450H (2009, Gen 3) imported from Japan, air suspension, no sunroof, right steering wheel.

exomen · January 30, 2023

On 1/17/2023 at 3:43 AM, Grey RX said:

Finally tracked down my invoice for this. Sorry for delays but hopefully this will be useful for someone. The error message the dealer uncovered was C1380 Stop light really malfunction. The relay replaced was part number L895A0-30010. The dealer also describes having removed gloves and trims to gain access to the relay.

Sad to say my problem has returned. Since I have been getting a lot of misting of the front windscreen and it has been raining a lot more, my suspicion is that there is a leak which is getting onto the relay.

Got exactly the same issue. RX450H (2009, Gen 3) imported from Japan, air suspension, no sunroof, right steering wheel.

Noticed rear break lights staying ON permanently, then found small pools of water in cavities of the trunk and 1-2cm paddle of water in the base of the Battery.

Front left passenger floor was a bit wet. I thought it might've got to the front from the back. I went through everything that is above the floor mat and it looked dry.

Removed rear covers and found a number of cracks in the factory sealant. Locations are as follows:

roof rack rails (removed plastics, cleaned and sealed - front and back)
back door fixings, door hinges, bases of door struts (removed plastics, cleaned & sealed) - this guide explains how to remove them
rear stop lights (removed, sealed, replaced the base rubber pads)
rear bumper (removed, cleaned, sealed all the body links where sealant was present)
plastic air vent on the right side of the rear bumper (cleaned, sealed)
plastic air vent on the left side of the rear bumper (cleaned, sealed)

Soab was still leaking a bit from somewhere.. so I went through the frame at the right rear bottom with sealant. Will see if it helps.

In regards to water in front passenger seat, I read on forums that it could be aircon drainage leaking, but I struggle to figure out what I need to look for and where. Removing front panel is pita.

Can someone tell me where exactly I can find a stop light relay?

I figure leak may also be somewhere close including probable issues with aircon.

Any info will be appreciated. Thanks.