electrical issue with stop lights

I have 2013 Prius C one, not V. There are some similarities with Gen 3.

You were leading the thread I mentioned on Gen 3 a few years ago. Was the issue resolved? What was the problem?

I scanned all ECUs today with Techstream and got only one active C1464 (right front speed sensor). The OP in Gen3 thread mentioned same thing. Coincidence? Maybe... Would be nice to know what the problem was. Can a shorted speed sensor cause these problems?

I cleared the code. Drove the car around with Techstream running and looked at wheel speeds. Everything seems normal. All 4 speeds are the same and match the speed of the car. No lights on the dash.

I checked the 12V battery. Did the recommended test with ignition off, 30 seconds high beam on, and the voltage was 12.2V. The manual says above 12V is normal.

The stop lights turn off if the car is either running, or ignition is in the "ON" position. With the ignition "OFF", the lights stay on and never blink.

No evidence of rodents under the hood. Everything is pristine inside near the brake pedal, no water damage, no dirt, etc.

Seems difficult to get to the ECU connector. I couldn't even see it. How hard is it to get to?

 

Thank you for the diagrams. They are very helpful. The power management ECU is inside, connectors look pristine. It looks like the primary suspect is a faulty signal coming from the skid ECU, which is outside. I am going to try to reseat A41 connector. Sounds like I need to remove wipers and the grill. Time to clean the intake mesh on the grill, I guess.

I am surprised there is no fault code. If skid ECU sends an erratic signal to illuminate the stop lights, it should know that the ignition is off, and the brake pedal is released.

 

Took the car apart to get to the A41 skid ECU connector. It was very dirty on the outside, but no visible damage. Unplugged it. Lights went off. Cleaned a bit the outside part. Plugged back in. Lights flickered for a few seconds and then came back on steady. Unplugged it again a couple of times, the lights go out with connector unplugged, but are always steady on with connector plugged in. Looked closely at the wires mentioned above (3, 6,33). Wiggled them a bit. Nothing. No visible damage to any of the wires.

Took the right front ABS sensor out from the hub. The sensor itself looked good. No visible wear at all. Dash lights and C1464 are on again. Wanted to disconnect the sensor under the cover in the wheel well but could not unlock the connector.

I am out of ideas.

 

How can I confirm it is a skid ECU before committing to a difficult and expensive repair? Yes, combined ECU and actuator. Is there a procedure to test pins on the A41 connector and confirm that, at least, relevant pins 3,6,and 33 are not shorted to something else?

Also, is there a close up on how to disconnect right front speed sensor on a prius c? It is under a wheel well cover that I can't remove, difficult to reach and see, attached to the metal frame. I can't see where the lock is and how to unlock it.

Thanks.

 

Here are a few photos of the connector

 

If the wiring is short, and both wires are not powered while disconnected, it can create a problem when connected, if a signal from ECU should go through one wire and not another. But the ECU might be fine.

 

The car died today in the morning. I drove it yesterday. Parked it. Today in the morning before starting the car I heard rapid clicking from a relay. The picture is attached. The car looks completely dead. I pulled it out. Clicking stopped, but if I put it back in clicking continues.

The diagram says it is a DOME CUT.

 

12 V battery was causing all problems. Hooked up a battery from another car. Everything is fine, no lights. Speed sensor lights are still on, but that is ok for now. I hope I don't have a short somewhere that drains the battery...

Update: stop lights are back on with ignition off They key again does not work. This is with another 12V battery hooked up with jumper cables, with OEM 12V battery removed. The OEM battery when removed today showed 9.4V.

I am measuring 0.45A parasitic current with the STOP fuse removed. It is a lot. How do I find what is causing the current? Is there a diagnostic procedure to track it?

Thanks.

 

With the stop fuse removed, car locked and let sit for 30 min, the drain current is 20 milliamps. I think, this is acceptable.
I wonder if my problem could be caused by a short downstream from the stop fuse, such as flooded taillight connector.
The diagram shows A50 junction connector, 3C-3D instrument light assembly, radio sensing condenser, M46 junction connector, and M5 and M6 combination light assemblies and SM1 wires
What is most likely the problem? Is there a good way to test? Just look at each component one-by-one? Do any of these components get power with ignition turned off? Which of these components could energize stop lights if shorted with the ignition turned off?

 

It is not back lights. Unplugged them one-by-one only to see the remaining two lights stay on.

 

Fully charged and tested OEM battery. Voltage seems fine (12.2 V with ignition off and 14.2 with ignition on). Load tester showed 220 CCA, battery nominally rated for 272 CCA. Says 66%. All green. Battery isn't new but does not look dead. Tried two other batteries, and a jump starter. All batteries are not new but with larger capacity and regular size. Same issue with lights (stop lights stay on). Now I have the battery on alligators just sitting on the floor.

Tried the back lights today. Back lights flooded with rainwater many years ago. Drilled weep holes. Never had a problem, but there is dirt on the inside and on the connectors. When took off the rear right light, the stop lights flickered and went away. I thought I got it. But then they flickered again and were going on and off for a while. Cleaned all connectors, took all light bulbs out, tugged the wire going inside the body. Nothing. Then disconnected left, right, and top one-by-one. Nothing.

Sometimes stop lights go out, more often after a long drive (I mean, with ignition off; when ignition is on, everything works normal). Sometimes they flicker, more often they flicker when I just connect the battery. They can flicker for a few seconds. Then they stay on.

If the car is off and let sit for a while (30 min) current is 20 milliAmps with STOP fuse removed. With STOP fuse in, the stop lights are on, and the current is like 0.5-0.6 Amps.

What else can I check?

Thanks.

 

Both, my original switch, and another brand-new switch I just bought from the official Toyota dealer failed the test "1 (OUT) -2 (GND) Ignition switch off, brake pedal not depressed Below 1 V". The voltage is ~12V instead of below 1V. It looks like both switches have a voltage leak onto pin 1 OUT when the pedal is not depressed, which causes my stop lights to stay on.

I also noticed that the last test "4 (ACC) -2 (GND) Ignition switch off" on both switches gives me a reading that jumps between 6V and 9V with the ignition switch off, which is out of spec. With the ignition switch on (not listed above) the voltage is ~12V.

Will try another switch.

It is difficult to test the switch. The connector wire is too short. I was only able to remove the lower left panel (in front of the computer), not the central lower panel under the wheel. With the lower left panel removed there is just enough room for my left hand to hold the switch with my fingers. After several failed attempts and a blown STOP fuse, I found that the best way is to use 14-gauge solid wire for pins 1 and 7, and 18-gauge solid wire for all other pins together with small alligator clamps connecting these wires to the multimeter.