Hey everyone,
I’ve been dealing with a really strange issue on my 2010 RX450h and I’m hoping someone here has seen this before.

Whenever the temperature drops below about 45°F, the car refuses to unlock with the key fob. The smart key doesn’t get detected unless I touch the Start button with the fob. After it starts, I get these warnings on the dash:

• Check AFS System
  
• AFS OFF
  
• Traction Control
  

I also notice the anti-theft/security light doesn’t blink like it normally does.

Here’s what I’ve tried so far:

• New key fob battery
  
• Tried a second (new) key fob
  
• Had the 12V battery tested at multiple places and was told it’s “good”
  
• Car starts and drives fine
  
• As soon as the weather warms up the next day, everything works normally again
  

The problem only happens when it’s cold, and we don’t get freezing temps often where I live, so it’s been really hard to reproduce.

Has anyone experienced something like this? Could this still be a 12V battery or grounding issue even though the battery tests fine? Any ideas or places to check would be appreciated.

Thanks!

 

How old is the 12 volt battery? What was the voltage when tested? Both off and with car running, although with a hybrid this is difficult.
12 volt batteries do last for many years in a hybrid and may pass some tests but still need to be replaced.
Did anyone check for stored codes?

I suspect you just need to buy a new 12 volt battery.

 

Many things come to mind.

1. 12V battery maybe be weak below required minimum below 45
2. Has anyone checked the trunk area where the battery sits. Some folks have reported standing water.
3. Remove all remote fobs form vicinity of the vehicle to rule out interference.
4. On a really cold morning use the key to enter the vehicle and see if the inside push button lets you lock/unlock [this bypasses the remote receiver and issues with signal being received from the key fob]
5 Try with the second key fob.

Any history of repair/tampering with electrical?
Any aftermarket accessory?

There are a few unexpected lights glowing in the dash? Can you please list all codes. [one thing I might try would be clear all codes, there are some downside to this so walk on this path with care]

Salim

 

I know this is an older thread but I'm having the same exact issues on my 2010 450h and I'm at a loss. Haven't pinpointed it down to temperature, but it's something I will be monitoring to see if that's possible. The car seems to appear "dead" at random, but then also go back to normal at random. For example, I had a work trip and when I went to leave for the airport, the car would not recognize the fob, no interior lights (but horn did work), seat and steering wheel memory was not working, and I had to start the car with the fob touching the start button. Parked the car for 5 days at the airport and when I got back, the car acted completely normal again without me doing anything, even though when I shut the car off at the airport and tried to start it again, it still appeared "dead". Then yesterday, I went to bring my daughter to school and again had the same issue where it appeared "dead" with all of the same symptoms. Drove her to school which is about 4 miles round trip (maybe 15 minutes total), and when I got back I shut the car off and then put it back on and everything went back to normal again (although I tried this a few days ago also and it did not go back to normal until I tried again about 3 hours later). Very odd and frustrating.

Below are the codes that appear when I have the issue (no recognition of the key fob, check AFS system message, have to start the car by holding the fob on the power button):

Body Control Module (BCM)

• B124B — Automatic High Beam System — Current
• B126A — Remote Starter ECU Communication Stop — Current
• U0208 — Lost Communication With Seat Control Module A — Current
• B124B — Automatic High Beam System — History
• B126A — Remote Starter ECU Communication Stop — History
• U0208 — Lost Communication With Seat Control Module A — History

Adaptive Front-lighting System (AFS)

• B2414 — Steering Position Sensor — Current
• B2414 — Steering Position Sensor — History

ABS/VSC/TRAC

• C1231 — Steering Angle Sensor Circuit — Current

Telematics System (TS)

• B15EC — Replace Back Up Battery — Current
• B15EC — Replace Back Up Battery — History

Smart Access (SA)

• U0142 — Lost Communication With BCM — History
• U0155 — Lost Communication With IPC — History

Below are the codes (listed as historical) that appear once the car goes back to normal again:

Adaptive Front-lighting System (AFS)

• B2414 — Steering Position Sensor — History

Telematics System (TS)

• B15EC — Replace Back Up Battery — Current

Body Control Module (BCM)

• B124B — Automatic High Beam System — History
• B126A — Remote Starter ECU Communication Stop — History
• U0208 — Lost Communication With 'Seat Control Module A' — History

With a multimeter I checked the battery voltage on the battery posts themselves (got 12.6), then on the wire ends connecting to the posts (12.6), and then also on the wire behind the main power fuse on the battery (also 12.6). I then checked the positive post in the engine bay fuse box and was getting 12.56v, which all seems appropriate. I then measured the same with the car on and got 13.6v everywhere. I also tested the battery with an Ancel battery load tester and the test result was "Good Battery".

Anyone have any ideas what might be going on? @Avocadoo , were you able to resolve this?

 

You probably still need a 12v battery. Those are the classic symptoms. Any other alternative problem source will be really expensive to fix, so go to checking the obvious and least expensive to fix source first.
Have the battery load tested somewhere. How many amps does it still have left? How old is the battery?

 

I should have mentioned, the battery was replaced in January of this year. Purchased from Toyota. The battery is rated for 355CCA and it measured at 366 and 12.73v using the Ancel BA101.

 

Then check your battery cables connections and ground wires in the engine bay. Plus check for stored codes.

 

If battery is good, next step should be a clean reset might clear out gremlins (if any).

I am discovering new things about 450H and any conventional thinking is not guaranteed. The machine is designed to conserve energy and the built-in smarts keeps shutting down system. Eg: If an audio source is not sending signal the Audi system turns off.

Shutdown RX.

Remove Key-fob from RX vicinity. and what 5 mins. Keep the front doors closed.
Disconnect the 12v battery for 30+ mins. [make sure you have access to the trunk area as the without 12v you will not be able to open the rear-hatch [you will have to crawl from inside and gain access to battery or the emergency please latch on the inside hatch.
Reconnect the 12v battery. Put back the trunk stuff etc to while away another 5 mins.
Then enter by the driver door and energize to get to Ready state ... follow the instructions on the screen and do not turn off till the screen says so.

Would it help? I hope it does.

There are some faults that need to be investigated

Salim

 

Yeah I actually did something similar last night. I disconnected the negative battery cable, and left it overnight disconnected. This morning I climbed through the back seat and reconnected the cable, and everything came on like normal (I will say, I did try this the other day as well, but only left it disconnected for about an hour, and when I reconnected the car was still "dead"). I will give your idea a shot if my overnight disconnect didn't work. I appreciate the thought.

And just to respond to @Clutchless , grounds were my next go to (I did check the battery ones, but not the engine bay). As far as codes, the codes I listed in my initial post when having the issue, always reappear (the same exact ones). And then when the car fixes itself, the historical codes I listed always appear (which are different than the ones when the issue is happening). They do not change in either scenario.

 

Just wanted to give an update in case it will help anyone else searching on here with a similar issue.

So I turned to Meta AI for some help and explained the issues and symptoms I was having, how it eventually comes back to life as if nothing happened, and seems to be related to weather (cold vs warm temps). At first it suggested that one of the main fuses (pn 82620-48160) in the engine bay fuse box may have resistance due to oxidation or the spades not making good contact when it's cold out, as this fuse provides power for things like the Body control module, which controls the AFS and other related items. So I removed that main fuse (which was a big pain as it's held on by 3 bolts on the bottom, so the majority of the fuse box needs to be pulled up/removed), cleaned the fuse prongs with deoxIT D5S electrical cleaner as well as the spades within the fuse box, and then also used a pick to bend the spades back a bit to cause more tension on the fuse prongs when the fuse is installed. Put everything back together, but unfortunately on the next cold day, the car was dead again.

So the next thing it suggested was to use a multimeter to test some fuses within the engine bay fuse box to see if they have voltage when the car is dead. It said to check the following as they could all be related to the issues that are present when in a "dead" state:
10A ECU-B NO.1
10A DOME
7.5A ECU-B NO.2
7.5A IMMOBI
7.5A AM2

Luckily the next morning it was dead again, so I checked each of the fuses for voltage and all returned 12.5v aside from ECU-B NO.1 and DOME. Meta suggested wiggling these fuses to see if maybe there's a resistance issue on either of them, and when I did that on the DOME fuse specifically, the car came back to life. A few seconds later the car went dead again, so I did the same thing and the car came back to life again (and both fuses now showed 12.5v also).

So Meta AI suggested removing the fuse, getting brand new quality fuses and before replacing them, clean the spade connections on the fuse box side with DeoxIT cleaner, and use a pick to bend the prongs a bit so that there's more tension on the fuses. So I did that for both the DOME and ECU-B NO.1 fuse holders (even though technically it was just DOME that seemed to be causing the issue, but they're right next to each other so I did both). I also bought Littelfuse brand fuses. This brand is used as a factory option by many car manufacturers, including Toyota. I did notice that the original fuse brand was PEC, which according to Meta AI, Toyota uses both PEC and Littelfuse interchangeably. So I went with Littelfuse since it was available at my local parts store for about $6 for a 5 pack.

Although the weather has been getting a bit warmer now, I've had about 4 days of mornings in the 40's (which is when the issue would present itself) and I'm happy to say I have not experienced the "dead" issue. So I am hoping that this has resolved the issue and may help someone else in the future!

 

Well done.and keep us posted on your fix. AI has helped me out on a couple of repairs during the past year or so.