electrical issue with stop lights

I've got a strange issue with some electrical components in my 2013 Prius C one. Today in the morning, the electronic key did not work. Key battery is new (later verified proper 3V), another key did not work either. I was in a hurry, opened the car with manual key. 20 minutes later when I parked the car, I saw that all 3 stop lights were erratically blinking even with ignition turned off. When I came home, I turned the ignition off and noticed that the inside fan stayed on. The stop lights would either blink erratically or stay on. I tried to diagnose the issue with Techstream, but found nothing. I tried testing stop lamp switch with Techstream, and the test seems fine. Stop lights would turn on for 3-5 sec and then go out, as described in the test.

The inside fan stays on even after car is turned off. The only way to turn it off is to actually start the car, then press the "off" button, and then turn the car off.

The door locks used to click and lock when the car reaches a certain speed (like 3 mph). Now they click right after I start the car. I noticed that the car randomly locks itself.

Electonic key does not work. Neither lock, unlock, or panic button. Manual key works.

The 3 stop lights (one on each side and the bar above the hatch window) stay on after ignition is off.

My first thought was bad stop lamp switch. I took it out. Stop lights went out, but I can't drive, because the transmission shifter is now blocked. The electronic key still does not work even with stop lamp removed.

I can't think of any reason like accident, flooding, etc.

Any ideas of what the problem might be or how to diagnose this further?

Thanks.

 

When the key battery was old, the key would gradually stop working. It would work only sometimes, from a short distance. Today both keys abruptly stopped working. One key has new battery. It worked fine yesterday, no signs of failing. The keys did not work today at all, not a single time.

Good idea to check 12V battery health. It is old.

 

I replaced the stop light switch. It did not work

I noticed, that if I remove the switch, the car seems perfectly fine. The key works flawlessly, tried it 20 times. The inside fan stops as it should. But I can't drive like that because the shifter is locked.

With the switch installed the car drives fine, the stop lights work as they should, the fan starts and stops as it should, nothing wrong is noticeable. However, once I stop the car and turn the ignition off, the stop lights stay on. They don't blink anymore. The fan stays on but stops if I push on the brake pedal. Then it resumes if I release the brake pedal. To turn it off I need to start the car and press the "off" button. Then the fan stays off. The electronic lock/unlock key actually works sometimes, but more often it does not. The car also often locks by itself.

The lights were off when I was changing the switch, but they came on immediately after I plugged the new switch in without even installing it into the bracket. Lights never came on with the switch removed.

How can brake lights stay on with the switch depressed? Is there another way for the brake lights to turn on bypassing this switch? Is there some kind of relay that could be getting power around the switch when it should not?

 

I never determined the switch was bad. I tried to replace it, and it did not work.
When I plugged the connector the switch white cylinder is out, as if the brake pedal is depressed. I pushed the white cylinder into the switch (as if releasing the brake pedal), but lights stayed on. This is all with ignition turned off.

 

With the 7.5A STOP fuse removed the lights stay OFF when the switch is plugged in regardless of the switch position, depressed or not. The electronic key works perfectly too.

 

With the fuse installed the only way to turn the lights off is to physically disconnect the switch. If the switch is connected, lights stay on regardless of the switch position. This suggests false control signal to the switch. Do you know where is the connector discussed in this thread? Rear Brake lights stuck on all the time | PriusChat

I just replaced the stop switch with a brand new one from the Toyota dealer. It should not be faulty.

 

Prius C one

 

So, it could be a corroded connector on the ECU or the faulty ECU. I live in MA near the ocean. Corrosion is likely. Do you know where the ECU connector is with wires going to the switch?

I don't have cruise control, but it is probably irrelevant. ECU can still send an erratic signal.

 

Is this the connector on the ECU?