Auto High Beam Dead

• Windscreen clean (in front of the Forward Recognition Camera, and Automatic Light Control Sensor)?
• Are the wipers parked in the right spot?
• Is the Headlight control wand on AUTO(might work on Head too?)?
• Were you going fast enough - it doesn't work at low speeds?
• I assume you were going forward only

 

The headlights are always controlled by the main body ECU, and if the high and low beams work when turned on manually, it’s unlikely to be a problem with the main body ECU outputs (HRLY and DIM) or a fuse or relay. There aren’t any fuses dedicated to the automatic high beam system, just those that power the headlights, main body ECU, and forward recognition camera, which if blown would cause other symptoms or warning lights.

I never use the automatic high beam feature myself, so I don’t know if the switch is supposed to be momentary or latching, and neither the Repair Manual nor the Owner’s Manual says for sure. If the switch is supposed to latch (press once to close, press again to open), perhaps it has failed and now works only in a momentary mode (press to close, release to open). This could explain the behavior you describe: the main body ECU detects that you’ve pressed the switch—which also tells us that the wiring to the switch is good—but then when you release the switch, the main body ECU disables the feature, as though you’d pressed the switch a second time.

What happens if you press and hold the automatic high beam switch?

With a Toyota Techstream diagnostic system, you could also check the Body Electrical > Main Body > Data List display. This would show the condition of the automatic high beam switch and the other headlight switches, as detected by the main body ECU, and also the automatic high beam system status (Auto H Beam STS0):

Undetec: Undetected
CAM NA: Camera detection malfunction
No sens: No detection
Hlight: Oncoming vehicles with headlights on
Taillgt: Preceding vehicles with taillights on
Speed: Vehicle speed
Daytime: Daytime state
Village: Urban area
Malfunc: System delay​

 

I usually don't have the occasion to drive at nite, but have found the auto high beams work very well. The only problem I've had is in the auto-high beam button... I had to notch the seat back a bit so that my knee didn't keep turning it off

 

You’re most welcome.

I think you’ve found the problem.

There isn’t a latching relay; on my car, the switch itself has a mechanical latch: a first push closes the switch, which also turns on a green LED on the switch and latches it into a noticeably recessed position, and a second push opens the switch, turns off the LED, and returns the switch to its usual position.

If the switch on your car is behaving like a momentary switch and won’t stay closed, then the latching mechanism has failed, and the switch assembly should be replaced. Toyota calls it the No. 2 Combination Switch Assembly, and for models on which the left button is blank, the catalog says the part number is 84010-47250. (See item ⑦ in image 6 of Figure 84-01, Switch & Relay & Computer.)

I imagine this would be a warranty repair; if not, the surround (the Instrument Panel Finish Panel Garnish Assembly, to its friends) just unsnaps, and the two claws that hold the switch assembly in place can be disengaged with a screwdriver.

 

Not exactly the same issue, but I and a few others in this thread, Automatic High Beams Not Functioning? | PriusChat experienced Auto High Beam spontaneously canceling while in operation momentarily for a minute or so and during that time, the high beam itself becomes unavailable unless you manually switch off the Auto High Beam switch under the dash to the left of the driver. Read comment #18 Automatic High Beams Not Functioning? | PriusChat in the thread for a detailed description of the event.

I have taken this issue up with my dealer during my last routine maintenance. They found no error code. There was no service bulletin from Toyota about Auto High Beam. And since it was during the daylight they could not reproduce the problem, thus did nothing about it. I then escalated the issue to Toyota Headquarters. They were pretty quick in getting back to me after leaving a message via the web page, but the Toyota rep who called me after doing some research said, "It is designed to behave like that, and it is not malfunctioning of the system." Apparently, Toyota programmed the Auto High Beam to cancel at random and disable manual high beam as normal procedure. I have no idea why. I no longer use Auto High Beam.

 

The situations in the above-mentioned thread, while driving with the Automatic High Beam operating, the Automatic High Beam indicator in MID (on the right side of dash, #3 in the pic) and the high beam indicator on left side of dash turns off momentarily (#1 in the pic below). Automatic High Beam Switch under the dash in the left of driver stays ON (#2 BLUE ARROW).

Sequence of event is exactly as described by @liquidtenmillion.

 

On my car, the Automatic High Beam Switch (#2) is functioning normally, that is press on stays on until press off to stays off. Yeah, your's sound like physical damage to the switch itself.

 

That, I don't know for sure. My car is not near me right now. I have to check it later. Sorry.

 

Ah.... bony knee caps, ugh.

 

Yap, I just confirmed on my PRIME. When Auto High Beam switch is pressed to ON, the light is on and the switch physically stays depressed slightly. $100 for a simple toggle switch, what a racket.

 

That's spare parts for you. I would imagine that it's a rarely ordered part, and cost of parts distribution add up for something like that.

You might get one from a wrecking yard?

 

My switch works fine, but I don't use Auto High Beam for the reason stated in #8. I can sell mine to @Prodigyplace for half of the retail price!