My friend has an 04 RX-8 base automatic . It was running great. Turned the car off one night, the next morning got in it started it up, and all of a sudden, the steering light, ABS light, brake light and check engine light came on. so i turned the car off, started it again. The same thing. then i took it for a drive and noticed that the speedo was not working and neither the cruise control. Now while driving it, all these lights would go off and on intermittently. When the lights go out like they should be, the speedo works and the cruise works fine. but as soon as the lights come back on, the speedo and cruise quit working. Now i pulled the check engine code with my scanner, and it read P121 (LOSS COMMUNICATION WITH ABS MODULE) so i cleared the code and as soon as the lights came on, the check engine light came back on. I then checked the ABS plug to make sure it was tight. I unplugged it and cleaned the contacts and no luck. Still was doing it. So i took it to Mazda and had them do a diagnosis on this problem. They said it was the speed sensor that is bad in the trans. So they put a new speed sensor in and it was working just fine. No more lights. So i started to drive it home, and after 10 miles, the speedo stopped working and the lights came back on. So i took it back to Mazda, and they can't fine what the problem is. It appears to be a short of some kind. Anyways, just wondering if anyone had any suggestions or have had this happen to them.

 

I remember some really weird stuff that had to do with LED lights and I think the 3rd Brake light. Is it by chance burned out?

Other than that, clean and check all the grounds, including the battery cable. Sounds like the computer is getting something that is confusing the hell out of it.

 

Loose battery terminals can do that.

 

Oh ok. I know the battery terminals are tight. But I didn't check the 3rd brake light to see if it is burned out or not. I'll check and see. Thanks

 

bump. Anyone else have any suggestions. Or have had this happen to them.

 

bump......................... suggestions!!!!

 

I take it the brake light was not the problem?

Best I can guess is go through the grounds. Check the ground part of the $100 thread for the common ones. I think something is inserting stupid in the electrical system, that is the best way to do it.

 

Ok, i will check the grounds as well. Yeah the brake light/lights were fine. Still trying to figure it out today.

 

A dying battery can do that