Error Code P0720
 

Got a 2010 Mazda3 with 2.0L showing a Output Speed Sensor error that won’t go away. Seen to have tracked it down to be the Vehicle Speed Sensor that’s between the transmission and firewall. Has 3 wires going to it from the TCM that are Power, Ground, and Signal.

With KOEO:
Yellow wire (Power) shows battery positive backprobed.
Red wire (Signal) shows 3.6 Volts while backprobed and 3.6 Volts when unplugged from sensor.
Black shows 10 mV.

For continuity test with TCM plugged in I get OL with DMM lead on yellow and the other DMM lead on battery negative.
OL with DMM lead on signal at VSS connector and other DMM lead on battery negative.

Only thing that throws me off is when I shake the TCM connector the voltage I get at the Signal wire VSS connector fluctuates between 2V and 4.8V.

Shouldn’t the signal wire be showing 5 Volts? Any other tests I should perform before I buy a new TCM, as I am under the assumption it has a short to ground inside the TCM.

I did fix the p0720 code, it was being thrown due to only getting 3V on the signal wire going to the VSS (output speed sensor) located on the backside of the transmission. Sent my TCM to Module Repair Pro through an eBay listing and all my problems were resolved.

EDIT: Did you check the voltage going to the OSS by back probing or with the sensor unplugged? You could be getting voltage drop through to much resistance in the TCM or the wires.

unplugged.
I also sent my OEM module for repair to services I found on ebay, pulled used one from junk yard while mine was getting fixed. Replaced with used everything worked fine for 1,5 years. Tried to replace it with refurbished recently and its way worse so had to put old one back. Wasted $300.

Can you sent me the name of the shop you used?

Thanks in advsnce.

https://www.ebay.com/itm/33231210099...mis&media=COPY

That’s the service I used on eBay, you sure you replaced the output speed sensor and not the input speed sensor on your tranny tho right? If I remember correctly they’re the same exact sensor on the 2.0 and are interchangeable, may be a simple way to see if it’s just the sensor instead of the wiring/ TCM causing the problem.

You got exactly 5V off of one of your wires (signal) with it unplugged right?

Thanks for the link!
And yes, I replaced output (I have 2.5 but should be same as 2.0) located on differential behind metal cover. First I got aftermarket from ebay for $20 - nothing changed, then I got OEM for $260 - still nothing. 5V unplugged, yes.

Next step, I think, is to use ebay services again.

Thoughts?

Honestly not too sure cause Id imagine that if the TCM is at fault you would at the very least have some strange multimeter readings as far as the 5V ref, power or ground to the OSS. Only thing that comes to mind is backprobing the sensor connector and testing for any resistance in the wires between the sensor connector and Tcm connector

I'll do that. Thanks again!

Ok I did back probing and a connector and reading were the same - 5 v. But here an odd thing : after each ignition cycle voltage reading changes sometimes reading 3,5v 2v or even 1,7v. After another cycle back to 5V.

So its TCM then?