Hazard light temp fix consensus

If you mess with L55 pin 8 you won't have hazards at all, even when you want them.

If you disconnect A58 pin 10 (HZRI) you just won't have the faster-with-road-speed unwanted ones.

If you just back the terminal out of the connector there (like most Toyota connectors, there's probably a primary locking lance holding the individual terminal in place, and a secondary lock for the connector that secures all the terminals), then all you have to do is pop it back in after the actuator's been replaced.

Or you could leave it disconnected, as no one has yet explained why the skid ECU needs to know when the hazards are on, anyway.

Or you could put a diode there, so the ECU could still know when the hazards are on (for whatever reason it wants to know that), but it wouldn't be able to flake out and make them flash.

 

The Repair Manual (more info) for 2012 describes the HZRI terminal of the Skid Control ECU as a “Hazard warning switch input,” but that might be an error in the documentation, if it it’s actually intended as an ECU output. It’s certainly wired that way, in the sense that the ECU can activate the hazard warning lights.

The publications for 2012 models don’t discuss why this connection exists, but in New Car Features for 2016 and later models, Toyota explains, “When emergency braking, the emergency brake signal function automatically flashes the hazard warning lights in order to reduce the risk of being rear ended by a proceeding vehicle.” It may be that the HZRI output is for similar behavior on earlier models.

 

It's weird, though ... there's not just the description "Hazard warning switch input", but also the mnemonic HZRI. And yes, it's wired in such a way that pulling it to ground makes the hazards go on, but that seems like it'd be true of just about any way they could monitor that line as an input (other than going all paranoid about it and putting a diode there, as I've suggested as a workaround). I don't see a lot of evidence of them going to such lengths to protect other inputs in general. Mostly, I think, the ECU just isn't supposed to flake out.

When it does flake out, it doesn't seem to reflect any kind of intended ECU behavior, but only that the line is being pulled down by some kind of short to the adjacent SP1 speed pulse output.

This is puzzling too, though, because the distinctive thing about the hazards is that they flash in front as well as in back, and geometry already reduces the risk of being rear ended in front. So it would seem quite adequate to just flash the brake lights, and indeed the Gen 3 stop light "relay" has not one but two extra control inputs that come from skid ECU outputs, as seen in this earlier thread.

The thing I'll say for sure is that the manuals have some gaps around these details.