Lost ECU connection... no start on 2020 Corolla SE

Hey everyone, new here. My 2020 Corolla SE 2.0L died while coming to a stop light a couple of weeks ago. Got dash errors like ‘brake override system malfunction’ and ‘drive start malfunction, not ready to start.’

Backstory: I replaced the slave cylinder about a year ago, which was a pain since I had to drop the transmission. After that, I noticed ABS-related errors—secondary collision malfunction, speed control malfunction, parking brake malfunction, and ABS errors. Car still drove fine, so I ignored them.

Now, after the car died, my cheap OBD2 scanner couldn’t read any codes. My cousin brought over a high-end scanner, and it showed lost communication to ECU and an ABS sensor issue. Checked the sensors, and the front left ABS sensor was broken. Ordered a replacement on eBay (Toyota wanted $300) and installed it—car still won’t start, dash is still lit up.

Feels like it’s stuck in some safe mode. No spark at all. Either that or my ECU is fried. Any thoughts on what to check next?

Did you check the battery voltage? Needs to be at least 12.6-12.7V, but a strong battery will be closer to 13V. Also, make sure the cables are tight.

Haven said:
Did you check the battery voltage? Needs to be at least 12.6-12.7V, but a strong battery will be closer to 13V. Also, make sure the cables are tight.

Yeah, had AutoZone test it—they said it was bad, but I wasn’t convinced. Still, I bought a new one. I keep it charged using my Ford Ranger just to be sure. Battery charge is solid, and terminals are in good shape.

Best thing to do now is find the factory service manual and go through the troubleshooting steps. Look for any symptoms or codes similar to what you’re seeing and follow the procedures—way better than just guessing and throwing parts at it.