2006 LR3 had no crank/no start problem. Had numerous codes on display... HDC ... Trans Fault .... Parking Brake Fault.. Had it towed to dealer. $900 later they said it was battery.. Replaced and same issue 2 days later. Dealer looked at it again and said its a bad ECM and needs to be replaced for a small fortune!! Had enough of that so its sitting in my driveway. Borrowed a friends code reader and got "U0100 Code. Lost Communication with ECM/PCM "A". Wanted to find and send ECM out to see if it has an issue but cant find it. It does crank now but no start. Any suggestions?

 

"U" codes are only information codes. If it does not crank, this usually means lack of "grunt" in the battery so check its voltage. The other thing is a duff alternator will quickly wreck a new battery so check that as well. If battery is good 12.8V or above then check that it is the same at the starter motor (follow the positive lead). If no volts at all check main fuse across front of battery.

 

Its in the engine bay, behind the battery. If the battery is not properly vented (small tube attached) then battery vapors can corrode the harness connections. Its a bit of idly work to get to the connectors, but not hard. Just put some time aside to inspect them. There are plenty of images and such on Google and the forum to help you out.