2021 3rd Gen developed precollision system problem, won’t start

So today while driving on the highway, my truck suddenly showed an alert saying “Precollision system malfunction / brake override system malfunction / cruise control malfunction”. It was still driving and braking fine, but I pulled over and shut off the engine and started it again to see if the systems would reset and come back to normal. Instead my truck will not start.

Called ToyotaCare and they set me up with a tow. Unfortunately, the nearest dealership is currently closed and the others will close before we get there. So oops, looks like I’m stranded tonight, but I thought I’ll ask the wise folks here to see if they knew some magic incantation or things to try to get it back in working order. I visually checked some of the big fuses and they seem alright. I have a digital multimeter with me so I can pull out and check a few other fuses. Any ideas?

 

Oof

Do you have an aftermarket grille, pedal commander, or trailer brake system? Any other aftermarket parts?

 

A brake override issue will typically cause a pre collision and cruise control malfunction to occur

 

None of these. In fact the only aftermarket electrical thingie are my Alucab brake and canopy lights. I wonder if it’s one of those.

Anyway, I had a digital multimeter like I said so I went through the fuses one by one. To my surprise the fourth fuse I checked, a 10A one labeled “Stop” was blown. Put in the Toyota-supplied replacement and the engine started. Things look normal now and the truck drives. Would’ve been harder without the meter pulling out each fuse to visually check. Saved me spending the night in my truck in a dealership lot and worrying about my cargo during the tow.

 

This was like the quickest thread ever. Good job. Glad your truck is fixed and it was easy. Thanks for passing the info along.

 

Sounds like you have a short in your canopy brake light wiring. Shouldn't be too hard to narrow done since you know how to use a multimeter.

 

I guess because I wired it myself anything is possible. Although I promise you I’ve years of experience in electrical work and would have taken the steps to prevent a short. But it’s holding up now, I’m going to go home and investigate. Does the STOP fuse also wire to the brake lights? Does that mean a Tacoma will not start if the brake light fuse is blown?

 

You’re spot on, and my hunch was right. I had put a barrel connector for my third brake light and without thinking happened to have slammed the tailgate on it. This broke the connector and allowed the positive pin to short against the metal body ground. So much for my great electrical work. I’m glad I didn’t go to the dealership since the Magnuson Moss wouldn’t have saved me here. But I now know the truck will report a brake light fuse failure in a strange way like this and refuse to start up!

 

Simple view:


Extended view:

 

can anyone help clarify this and identify exactly what prevented the truck from starting and what the fix would be?

 

It was the shoddy 3rd brake light wiring I’d done for my canopy that blew the 10A brake light system fuse marked as STOP. It looks like the Taco will not start without this fuse. I’m yet to study the posted wiring diagram to understand why.

 

When you get it figured out please post up. A theory of operation would be nice.

 

The schematic shows that you have to step on the brake pedal to start the engine. So without power to the brake lights when you step on the pedal then the engine control does not think you are stepping on the brakes. no brake lights, no start

 

Looked over the schematic with that important kernel of information, let's see if I have this correct:
The brake pedal has a switch that has two circuits, one a MAKE and one a BREAK. The BREAK removes 12VDC from pin ST1- on the Engine ECU, while the MAKE applies 12VDC to the STP pin of the Engine ECU. A double safety measure, both have to happen for the Engine ECU to recognize the Brake pedal is depressed and thus allowing the engine to start.

Not shown on the schematic in post #10 is the actual Brake lights circuit which is controlled by the STPO pin of the Skid Control ECU (with hydraulic brake control, the OP and I both have a 2021 OR) which grounds the Stop relay coil thus energizing the relay and supplying 12VDC to the rear STOP lights from Pin 5 to Pin 3 of the STOP relay. Again the wiring is not shown to the Stop Lights, but that is where the power to the Stop Lights comes from.

I looked through the Fuse list and found that this 10 Amp STOP fuse has 22 different circuits it affects/effects (never have been able to figure out those two words). Toyota (maybe other manufactures too) has sure made things confusing, at one time a STOP fuse was for the Stop/Brake lights ONLY!!!