im a mazda tech and ive had an 06 mazda6 in the shop for a few weeks now. customer says that the car starts shifting poorly, at which time all the warning lights will start to flash or just stay on, the tach will pulse, and the temp gauge drops to cold. the car will eventually die, and then cannot be restarted. we have verified all of this so we know he isnt making things up.

each time we scan the computer and find about 7 dtc's. all codes are communication codes, u0101 u0121 u0073 u2516 u1900, and a few more that i cant remember. the dtc descriptions are all pretty much the same, the abs/tcm/ipc/pcm cant communicate with eachother. we ohmed out all of the communication lines and found that they are good. and since the abs/tcm/ipc all coomunicate to the bcm and the bcm then sends the signal to the pcm, we felt that the bcm was the problem since it was the middle man from those modules to the pcm. we replaced and reprogrammed it, and it actually got rid of half of the dtc's. the only dtc's that were left were pcm related codes, so we replaced the pcm too. but then every single dtc came back so now we are at square 1 again.

does anybody have any experience with this? im welcome to all educated guesses. nobody in the shop has any clue, neither do the guys at mazda techline. im ready to burn this car to the ground!

 

I don't know if this has anything that might help, but a friend had his F-150 in at Ford that was having many mysterious codes and it ended up being a bad ground on the motor. It only did it under a high Electrical load. The way he was talking it was getting Voltage spikes through the GEM and the ECM was picking up codes.

 

not a bad idea. it seems to be heat related because after dies, it needs to sit a while before it can be restarted. so ill have to check for an engine ground

 

Dear Sir,

Perhaps you're in the same situation as I was a couple of months ago...

You have with high probability (Like I had) some wires that are touching/rubbing against the chassis or communicate together) via short-circuit ...

Take a closer look at the wiring harness departing from the main fuse box (Motor compartment), going under the air filter, passing nearby the left headlight...

Some wires are probably rubbing against some metallic parts in this area...
(In my case, the dealer found 4 wires in short-circuit and some even were burned/melted at a location close to the left headlight)...

Unfortunately, to solve this problem, my dealer had to remove the front nose of the car, the left headlight and the air filter to have proper access to the damaged harness

I had almost the same symptoms: plus the horn was starting without warning and I had the headlight cleaner pump starting unexpectedly...

It was a one day job to repair the damaged wires but make sure you let pack/protect the repaired wires inside a rubber sheet to avoid this to repeat in a near future...

Ask the dealer to pay a special attention to the C-Bus wires (blue and red wires twisted together)... if they are damaged, the Instrument Cluster goes crazy...

This also generates a lot of ghosts error codes...

After this repair, the car was running just fine and the problem never reoccurred since...

I was absent all the time the technician did the repair, all the above mentioned was only reported verbally to me, so i cannot give you a more accurate location of the failure...

The only thing I saw by myself was the fact that, by slowly shaking this harness while the engine was running (important...) triggered the problem.

Hope this helps... Best Regards... & Good Luck...