C1237 - Speed Sensor Rotor Faulty
 

I've probably had this issue since I swapped a 3UR-FE into my car. We initially thought it was an issue with the CAN BUS translator between the 3UR ECU and the 86 Main Body ECU. After a few revisions and confirming with techstream, it is 100% an issue with the 86 ABS ECU or a faulty sensor somewhere and I can't seem to figure it out.

I could drive the car for hours on the highway but as soon as I make a hard right turn (sometimes long left turns like roundabouts) I get this code, C1237. Which disables the ABS ECU, speedometer stops working and with that the power steering stops working as well. I've wired a temporary switch to the ignition fuse powering on the ABS and power steering to turn off/on whenever it happens. This gets old real fast as the parking in my apartment building requires turning left a handful of times and it happens 2-3 times everytime I come home.

Using techstream, I can see the individual tire speeds and they all seem to be within 0-0.5 km/h of each other on turns where this issue occurs. I physically checked the sensors and they seem to be in good shape. Is there another speed sensor in the car I'm not aware of and the techstream is not showing? I did swap a T56 transmission in recently but even with the stock J160 trans it had this issue when it was mated with the V8.

I'm planning on installing a Haltech standalone ECU soon and I want to figure this out before doing so. TIA

What ECU and/or CANBUS translator are you using?

Since it's when turning to one specific side, my gut reaction would be to check for a loose wheel bearing.

If you've gone through the appropriate diagnostic chart here https://demos.starbase7.net/t3Portal/ and you still can't pinpoint, your last chance is going to be scoping the wheel speed sensor signals directly with a digital storage oscilloscope to catch the glitch responsible.

A loose bearing will 100% do that. I've had it happen at the track. But it has to be really fking loose. Also, check the cables, connections, possibly tires/wheels touching anything.

@geraldjust made it for me

Thanks, I'll try this if nothing works.

Well we found the front mount of the lower arm to be cracked on both sides. Just welded those up with a thick metal plate on the inside and will check the bearing today.

Fixing the mounts didn't do anything. Both front bearings are tight and spin freely. One of the rear bearings wasn't looking good and made a grinding noise when spun and the other wasn't far off. Replaced both for about $250. ABS is still throwing the same code when turning.

I'm starting to lean more on it being an electrical issue rather than a mechanical one. Something like whenever the power steering is drawing power when turning it somehow effects the ABS module's ability to read the speed sensors properly.

I know they both share the same main 80 amp fuse like everything else on the car except for the alternator. I'm also using that same fuse as a battery source for the additional load for my swapped engine ECU. Is it possible for the EPS to draw just enough power to mess with the ABS but not to blow the 80 amp fuse? If so, I might just wire it directly to the battery terminal and be done with this.

Fixed! Thanks to @geraldjust he was able to confirm my suspicion that it was an electrical issue. The first time I hooked up the techstream to the car it had multiple codes from the ABS module. I took a picture of them and cleared them. When the issue occurred it only threw the one code, C1237.

The last time we hooked up a third part scanner as techstream was acting up like it always does. It showed two codes C1237 & C1241. The new one is saying the voltage is either too high or too low.

I wired the abs module directly to the battery and it threw the same codes. Talking to Gerald, he said he had the same code whenever the battery voltage drops and the 86/BRZ usually idle with the alternator producing between 13.8-14.4 volts.

The Tundra system which my swapped engine is from idles between 12.9-13.2 volts. I hooked up two diodes to the alternator regulator sensor and now it idles around 13.8 volts. Took it for a spin and finally no codes so far :)