Long story short, I have an OBDII scan tool (Kiwi3) that I wanted to use just for information purposes, mainly to be able to monitor the tire pressure of all 4 tires individually. During this process, I noticed my instrument cluster was throwing all sorts of errors (smart city brake, engine oil sensor low, keyless system malfunction, etc.). The engine was not running, nor did I do anything that would issue any commands to the ECU. The app I was using is OBD Auto Doctor Pro. I disconnected the Kiwi3, and tried to start the car thinking it would just clear itself. All I got was a click. I tried that app to clear the codes but it didn't do anything. From what I was able to research, I performed an ECU reset in the following manner:

1. Disconnect negative terminal clamp from battery
2. Sit in driver seat, depress brake pedal 5 consecutive times
3. Wait at least 15 minutes. (I waited 20)
4. Reconnect negative battery terminal and start the vehicle.

This did not work. Same result. I have a second app called OBD Fusion. This app was able to read all the codes as well as reset. I performed a reset using this app. Even more errors appeared, there was a single long beep at some point, all indicator lights (including the screen) were flashing wildly. The lights then all went out, and the needles (i.e. fuel, engine temp?, etc) were just going nuts for lack of a better term. Now the vehicle is totally dead. I am sure that other than plugging in the Kiwi3 and just trying to read information and figure out how these apps work, that I did not do anything that would cause this. I am trying the 3 step process again, waiting for an hour this time. Is there anything else I can try?

 

You can not re-set a ECU by disconnecting the battery....This is with most all vehicles from about 2000 and newer sold in USA with OBDII ECU. The error causing the DTC are already in the monitors until they are resolved. This is a long time MYTH on forums. It will turn off the check light on the dash but that is really all it will do.

My guess is something got miscommunicated having to do with your with your immobilizer system mobilized. In which case it may be a trip/tow to MAZDA?

Good luck I am sure you will get it resolved. But in the future leave the battery connected unless you are changing it or doing a service procedure that requires the battery disconnected.

 

Yeah, I think you might be right. I did notice a light flashing that has a car and a padlock. I wonder if this would fall under warranty? The way I see it, I was merely looking for information. Granted the saying "there be dragons ahead" saying applies here. Maybe I should have just let well enough alone. I'm sure there's probably an analogy that would counter it.

 

So, an update. I called Mazda Roadside Assistance to have it towed to the dealer. When they arrived the guy wanted to try jump starting it first. It WORKED!! Started right up with only the flashing red brake light and parking brake lights for warnings. I took it out for a drive, seemed fine and had normal brakes. Might still need to take it down to see what that's all about but I'm considering myself pretty lucky. Also a little dumbfounded that a jump start worked and solved 99% of the issues.

 

Based on your first post and that the jump got your car started that would be the cables or cable terminals at the battery. Maybe you should service them?

its still a happy and no cost ending to a problem!