ABS and anti-skid ecu problem

I was driving my 2013 Prius C one at a slow speed today and 4 lights on the dash came on: ABS, Brake, ECB, and skid, when I tried to brake. I felt as if ABS was activated, but I was on a dry road. The brake pedal became softer, but I did not lose brakes completely. All 4 lights would go on and off while I was slowly driving home. The codes I read with Techstream are C1300, C1311, C1365, and C1466. Attached is
all the data I read for the codes C1300 and C1365, and from the Data List. I don't see any obvious brake fluid leak or loss of fluid in the fill tank.

What is wrong? How do I diagnose and repair this problem?

Thanks.

 

I have the manual.

C1300 calls for outright replacement of brake booster with master cylinder assembly.

C1311. I confirmed that live data responds to active test for ABS main relay. I can turn it on and off and see live data change accordingly. Next step is to check the harness and connector. Where is the skid control ECU connector A41? I don't even see it. How do I get to it?

C1365. Accumulator pressure sensor. I've got the reading of 3.7V. When pressed the brake pedal it dropped to 3.35V, then came back to about 3.8V. When I press and release brake pedal it moves around a bit, but not more than 0.55V per test guidelines. This looks normal to me. The next step is to replace brake booster with master cylinder assembly.

C1466. I looked at the live data while driving around the block. All 4 wheels report the same speed and it is close to the speedometer.

I also noticed that with ignition off the brake pedal on release makes a sound as if it was sucking air into the system. Don't see any leaks or fluid level dropping in the brake fluid reservoir.

Then I cleared all codes. After clearing the codes the car became "normal". Slowly drove around the block. Seems to brake normal. No more sound on brake pedal release. None of the codes came back.

Any suggestions what might be wrong? Is it the skid ECU (computer) failure, or brake actuator failure, or brake booster failure? Would the only option be to replace the brake booster assembly and the brake actuator assembly? This replacement seems involved. Is there a video for it?

Could all these problems be due to something else, such as weak battery?

Thanks.

 

Here are the relevant pages from the manual with the DTC detection conditions. A41 connector is on page 3 of C1311.pdf. It is the same connector as you show. How do I get to it? Would be a shame to replace expensive parts only to find out there is a bad connection or undervoltage. Thanks for clarifying booster vs actuator vs accumulator parts. It is confusing. I saw your post in Gen2 section, but I was not sure it applies to Prius C. You are right, Prius C is similar to Gen 3.

How do I diagnose this further? Do I need to replace the top part (brake booster assembly), bottom part (accumulator), both parts, or is the problem somewhere else since the codes are not coming back right away? For example, if the accumulator pump is failing, why would it throw C1311 code, which says ABS main relay has a problem?

Thanks.

 

You have much more experience than I do in looking at these diagnostics charts. Thank you for helping me.

I only have wiring diagram for Gen 3, not Prius C.

Looking at A58 and comparing it with parts of the diagram I have for Prius C, I see that BS - 15, IG1 - 16, BI - 14, and IG2 - 12. So, C1311 tells me that BS voltage was more than 3.5V while IG1 voltage was more than 9.5V (for more than 0.2 sec). The code C1365 with detail code 331 says that VACC voltage to the pressure sensor was out of range. As I understand, this VACC wire is internal to the "Brake Booster with Master Cylinder Assembly" and is not shown on the wiring diagram. The rear right wheel speed sensor are pins 22 and 9. I don't see the detailed INF code in my screenshots for C1466. I don't see the wiring harness (behind the cowl), but these speed sensor wires (pins 22 and 9) should travel to the wheel separately from BS, IG1, BI, and IG2, right? (Yes, they start in the same bundle, but the only connector they are together is A58)

Now this looks like an intermittent electrical problem. I cleared the codes yesterday and they did not come back. I will try to inspect the A58 connector on the weekend. I remember it was difficult to remove and install the cowl. It looks like an internal electrical skid ECU problem, but I am still not sure it was not caused by something else, such as, for example, an electrical leak to the ground from BS in the A58 connector or in the harness. Also, it looks plausible that an undervoltage on BI or BS (weak auxiliary battery) could cause this problem. Maybe I should start with auxiliary battery load testing?

Thanks.

 

You are right. Thanks.

The BS (pin 15) goes to 20A ABS Main No. 1 fuse and then to the battery. Zero BS1 voltage suggests that either fuse of the wire has an intermittent problem (open circuit). BI, IG1, and IG2 go into the ignition system. I don't understand how it works. Does voltage on IG1 and IG2 come from BI? I don't see BI voltage on diagnostic screens. Does zero IG1 and IG2 also mean that BI voltage is zero? The BI is fused with 7.5A ABS Main No. 2. Both fuses, as I understood, are in the engine compartment (passenger side). They are fuses 19 and 28 in the engine compartment: Fuse box diagram Toyota Prius C / Aqua and relay with assignment and location

Should I check these 2 fuses the next time problem occurs? If fuses are ok, should I then get to the A58 connector and check BS and BI voltages?

Thanks.

 

I wanted to check IG1, IG2, BS1 voltages while the car acts normal, but since I cleared the codes I don't have snowflakes anymore. The Data List does not show them. Is there a way to check these voltages? How do I get Freeze Frame data? Thanks.

 

I still need help with this. I cleared the codes and the problem "went away" until yesterday, when skid light started to flash again at random while breaking. Today all 4 lights came back on, but the codes are now different: C1238 - foreign object is attached on tip of rear speed sensor RH; and C1466 - rear speed sensor RH circuit. I took the right rear wheel off, unplugged the sensor, cleaned the connector and spun the hub by hand a few times back and forth. Then cleared codes. Next, while driving all 4 lights came on and then came off after about 10 sec. Now, there are no lights on the dashboard. I read the codes again and there is only one current code C1238 (though I cleaned it earlier today). The sensor wire connector looks fine. The freeze frame data shows erratic behavior of that sensor. Sometimes it shows 0 while driving, sometimes it shows something different from other 3 sensors.

It looks like either sensor tip or the sensor rotor is dirty or damaged. Unfortunately, the repair manual tells to "replace hub assembly".

How hard is it to remove this sensor from the hub assembly and clean it? Is it worth trying or should I just replace the hub? How hard is it to remove the hub itself? I saw horror videos that even a slide hammer is not enough to pull the hub out. This car has drum rear brakes, same as Yaris.

Thanks.

 

Thank you! I am trying to remove the hub. I took 4 bolts out (through holes) and presoaked the seam with penetrating oil. I have a 2-jaw pulley with a large slide hammer. I attached the jaws trough the 2 holes in the rotor. I hit it with all my strength and it does not move. It does not separate from the backplate. How do I take it out? Is there a trick to do it? Will I break the front rotor or pull it out of the hub cylinder if I hit it so hard? Whether I am replacing the hub, replacing the sensor, or cleaning the sensor I need to take the hub out. Please help.

 

Thank you! I pulled it out. But it came out together with the back plate! What do I do now? It is hanging on the brake line and parking cable. I supported it underneath, of course. But now I need to separate the hub from the backplate. How do I do this? Will I need to take the rear brakes apart, disconnect the parking cable, clamp the rear brake line and then bleed brakes? I have very little access now from behind, but I don't know how to push the hub out of the plate. Please help. Thank you.

 

Thank you! I got it out. I used a long bolt and a nut of a size slightly larger than the holes in the rotor. I put the nut behind the rotor, threaded the bolt in and then pushed the backplate with that bolt. I alternated several times between the opposite sides. The first two pushes were the most difficult. When the backplate finally separated it popped pretty loudly (1 pop on each side). After that it was easy, but I still had to switch sides 4 or 5 times. Had to be very careful while threading the bolt to make sure it pushes against the back plate and does not tocuh anything else. Did not have to do anything with brakes!

 

How do I know if the bearing is good or bad? It has no free play. The wheel did not move at all when I pushed it 3-9 and 6-12 o'clock. I can rotate the hub (removed from the car) by hand, but rotating it by just my pinky finger is pretty hard. It has some grinding resistance. With the tire on it spins fairly free, but there is a bit of intermittent grinding noise.