2016 Mazda CX5 no start, no crank

Hey everyone. I found the forum while trying to diagnose a no crank/no start issue very much like the one posted  here . 
I actually found useful information there to help me diagnose. But first some background.
The car has 150k km and never been on an accident. A couple of months ago I started noticing some "judder" when decelerating and then accelerating, specially at around 2000 RPM on 2nd and 3rd gear wich, to me, felt like the torque converter clutch slipping, so I started suspecting a bad solenoid or torque converter.
The issue became more noticeable with time. I took it to a shop, where they scanned it and reported that the TCM was showing a code for the electric oil pump that keeps oil pressure when the start-stop system is active.
Weeks later, the iStop system started malfunctioning with the light blinking amber, a message in the infotainment and a very hard judder after the car starting when the iStop system engaged. It was as if being hit from behind by another car. So, there was a visible symptom of the maybe failing pump.
Two days ago, my wife parked the car and got to the state where we are now.
It does not start, dashboard lights up, shows all kind of lights and after scanning, shows error U0101 (No communication with TCM).

What I have found so far is that the 15A "AT" fuse is blowing. If I disconnect the TCM plug, put a new fuse and plug the battery, the fuse does not blow, a scan shows a whole array of codes and the car does not start. I unplugged the electric oil pump in case it was shorted.

If I plug in the TCM, as soon as I connect the battery, the fuse blows, even with the pump unplugged. Check this video (it's in spanish but I think the point gets across).

The car is at an office building parking and I don't think I can get a tow car in there easily, so I would like to try and get it running ASAP to get it out and maybe do a better diagnostic later.

Would all the previous symptoms leading to this be related to a malfunctioning PCM? What would you test next?

Hey ertomas! I snipped the relevant part of the transmission wiring diagram for reference:

 

Based on your testing, I think it's pretty safe to say there's a short to ground inside the transmission. On this transmission, the TCM itself is integral to the valve body itself. That'd mean at least dropping the transmission pan for inspection and possible replacement. Programming would also be required after valve body replacement.

As far as getting it out of the parking lot, there are two things I can think of that you can try. One would be to cut the yellow wire in a repairable location near the transmission connector. Plug the transmission back in and see if the TCM will power up and communicate without power from the AT fuse. If you can get the TCM to communicate, the engine may start and allow you to limp home (which hopefully isn't far).

You can TRY a bigger fuse, but that comes with risks. Overheating terminals and wiring, for one. Damaging transmission internals would be another. I'd probably find a way to tow it home before doing this.

EDIT: I'd also suggest pulling the fluid level dipstick and check for coolant in the transmission fluid. If you find coolant, I'd go straight to transmission replacement.

Hello Tyler. Thanks for the suggestion.

I have a couple of questions.

One would be to cut the yellow wire in a repairable location near the transmission connector. Plug the transmission back in and see if the TCM will power up and communicate without power from the AT fuse.

1. Wouldn't this be the equivalent of the fuse being blown or removed? If this is the case, then no, it doesn't communicate this way.
2. If I wanted to confirm if there is a short with a multimeter there would be one or more pins with zero resistance when measured with the ground pin? I want to test the TCM connector and the wire harness itself.

 

For (1), it would be as if the the fuse is removed or blown, and looks like that wire can’t be bypassed since it supplies power.
For (2), you confirmed the yellow wire is shorted from the transmission as the fuse blows when you connect it and as Tyler pointed out. It’s possible, though unlikely, there is a short in between, but if the fuse only blows, consistently, when you plug in the connector to the TCM, I doubt there is a short in the harness.

Are there shift gear indicators in the dash? Can you shift with the accessories on? If you can't shift, override and move the shifter to neutral and try to start it.

- Nour

ertomas wrote:

1. Wouldn't this be the equivalent of the fuse being blown or removed? If this is the case, then no, it doesn't communicate this way.
 

It would be the equivalent of the fuse being blown, yes. My hope was to fully eliminate all other components and wiring powered by the AT fuse. That way, you can know for certain that the short is inside the transmission. Plus, I was kinda hoping the TCM would communicate with just one power source.

2. If I wanted to confirm if there is a short with a multimeter there would be one or more pins with zero resistance when measured with the ground pin? I want to test the TCM connector and the wire harness itself.

Pin A at the transmission connector would show zero ohms of resistance to ground (or very close to it) if you checked it with an ohmmeter with the negative lead connected to B-. However, if you cut the yellow wire like I suggested above and the AT fuse no longer pops, then the resistance measurement becomes redundant.

So, an update on this... 
The TCM is indeed fried. I replaced the valve body, the car starts and drives. 
 
​​​​​​The strange vibrating issue that I believe is the torque converter still persists. 

Thank you guys for your input. ​​​​​​