My wife has a 2010 MDX that's experiencing multiple concurrent issues.

A) Flashing D - When I start the vehicle, the D is flashing. When I change from P to R, there is a small engine rev change; but no sound or movement from the transmission. When changing from R to N, no sound or change. When changing from N to D there is a loud clunk that can be felt in the driver seat. Going in reverse is exactly the same. Clunk from D to N, nothing from N to R to P. Also, when in R, the vehicle does not attempt to move.
Note: The ATF was recently changed (using genuine Acura ATF), no shavings.

B) ODB 2 Link Error - When I start the vehicle and plug in my scanner to the ODB 2 port, it powers the scanner; but fails to read with the message "Link Error...". The scanner has worked on this vehicle many times in the past, so it's not a comparability issue; and I verified that the scanner still works by scanning my F150.

While there are multiple issues that can cause the transmission issues I'm seeing, my research leads me to believe it's a shift solenoid stuck open. That being said, a solenoid issue can be caused by an electrical issue, which could also be the cause of the ODB 2 read issue. I checked the fuses under the hood (both boxes) just to see if any were having issues, and none were blown. I'm about to check the ones in the cabin; but I wanted to check and see if anyone had any ideas of what could be causing this or things I should check.

Thanks in advance.

 

Update: I tried a higher quality ODB 2 reader which also received power from the port and failed to connect to the ECU. To add to the issues, there is also a slow parasitic drain on the battery.

I'm going to jack up the car and start looking for a break in the wiring harness as this is the only explanation I have for all the symptoms at once.

 

T

 

These modern cars are sensitive to voltage levels and any low or unstable voltages will cause the ECU to be confused.
Start by chasing down your parasitic draw. My 2007 MDX has a draw of 1.449 A as soon as I close the doors and it drops down to .255 A after the interior lights go out. These numbers are with my HFL (hands free link device) unplugged.
Here's a link to Skirmich's write up on his Transmission Range Switch/Netural Safety Switch.LINK

 

First, do or have a battery load test done

 

I tested the battery with my charger and it checked out, which means it's not shorted and can take a charge. It's not a complete test, but the batter is relatively new. I can get a complete test later, but it has been ruled out as the cause of this issue since the issue exists with the vehicle of and ignition in run and while the engine is running.

I also checked the voltage coming from the alternator and it's a steady 14.2VDC (~.1).

 

I checked the vehicle over end to end and could not find any issues with the wiring or signs that rodents had tried to nest there. I found no damaged (chewed or rotted) wiring harnesses and no ground connections that looked disconnected or corroded.

My next idea is to replace the ECU to see if something is wrong with the current ECU. Even though the engine starts and runs, that doesn't mean that some portion of the ECU is not damaged/broken. What I don't know is if the key is tied to the ECU, so if I replace the ECU, do I need to get a new key made to match it?

 

So, I gave up and took it to the dealer to get fixed. I was sure it was the ECU and I don't have a programmer or the time to get one and experiment. That turned out to be a good thing because the problem ended up being a faulty wire going to the MAF sensor. I don't think I would have ever found that in a million years.