Need help w/code 21

[DirtBoss]

2009 M8 RGT. About 10 seconds after startup it is throwing code 21 at idle.
Swapped ECU and knock sensor with another sled and it is still throwing the code.
You guys have any ideas?

Thanks

 

[matt159]

Since you swapped out the suspect parts, it makes me wonder if you have a break in the wire before the sensor.

 

[never enough snow]

Did you change the speedo as well maybe bad ? I have had a couple bad one's showing false codes.

 

[DirtBoss]

Both good ideas. I will see what I can find.