No start no crank / codes U0073 / U0140 - 2006 Buick Lucerne

U0073 - Definition: Control Module Communication Bus "A" Off
U0140 - Definition: Lost Communication With Body Control Module

What needs to happen is the cluster can be commanded to sweep gages using the GM Tech 2 scan tool. Keep in mind that the gage testing and any programming needs to be done at a GM dealer using the GM Tech 2 scan tool. If they respond correctly to that command that means the gages and wiring to the gages is fine and the part(s) responsible for sending info to the gage is inaccurate. If they don't sweep ok then suspect a faulty cluster. To do the sweep test it needs to go to a GM dealer though. The gages not being accurate is common on the older year trucks and a cluster is the fix (along with programming the new cluster using GM software).

Check this information about #PIT4730: Additional Diagnostic Information For U0140 Or U0073 - keywords BCM comm communication cycle DIC door freeze gage gauge inop inoperative int intermittent LAN locks message no service speed speedo - (Oct 3, 2008)

Subject: Additional diagnostic information for U0140 or U0073

Models: 2008-2009 Buick Enclave
2006-2009 Buick Lucerne
2006-2009 Cadillac DTS
2007-2009 Cadillac SRX
2008-2009 Cadillac CTS
2007-2009 Chevrolet Avalanche, Silverado, Suburban, Tahoe
2006-2009 Chevy Impala
2006-2007 Chevy Monte Carlo
2008-2009 Chevy Savana
2007-2009 GMC Acadia, Sierra, Sierra Denali, Yukon, Yukon Denali, Yukon XL, Yukon Denali XL
2008-2009 Hummer H2
2008-2009 Pontiac G8
2007-2009 Pontiac Torrent
2007-2009 Saturn Outlook, Vue

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern: Some customers may complain of one of the following symptoms:
• Door locks cycle while driving
• Intermittent No Start
• Service Stabilitrak DIC message
• Speedometer and tachometer freeze while driving

Along with these complaints DTC U0140 00 and/or U0073 71 may be stored as a history code in any GM LAN High Speed module.

If the data circuits (2500 & 2501) have experienced an "intermittent" short to ground or short to each other "2 times" within a period of less than 1 second and then go back to normal, the BCM may appear to be "off-line" on the high speed buss. This intermittent scenario should not cause other modules to lose communication, only the BCM. If this situation happens, the BCM will not start communicating with other modules again until the key is out of the ignition and the BCM has timed out (approximately 20 minutes).

Typically the customers complaint will be intermittent and usually occur when driving over bumps/rough roads.

Recommendation/Instructions:
If DTC U0140 00 or U0073 71 is set only as a HISTORY code in any of the high speed modules, refer to "Testing for Electrical Intermittents" in the service manual to reset the DTC and diagnose the location of the fault.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.


Also coudl visit your delaer and ask fot this Bulletin:
TSB Number: 08-07-30-021 NHTSA Number: 10025402 TSB Date: April 1, 2008 Date Added to File: August 6, 2008
Failing Component: Engine And Engine Cooling:Engine
Summary: Loss of high speed gmlan communications, intermittent no crank, ipc gauge fluctuation, intermittent door lock cycling, transmission may not shift, DTCs U0073, U0100, U0101, U0102, U0140 (repair backed out terminal in transmission harness connections).

Test it and lkeep us updated.

I don't know where this other guy got his information but it is wrong ! U-0073 is telling you that there is a problem with the High Speed Communication Bus and the modules listed below are on that Bus.
Audio Amplifier, BCM, DDS, DPM, DRR, Object, Alarm Module, PDS, Radio, RCDLR, SDM, TDM and U - 0140 is telling me all these modules lost communication with the BCM- Body Control Module The first thing I would do when I get A vehicle like this is to check power and grounds to the BCM, You see with out the BCM working nothing is going to work.
The body control module (BCM) activates the high speed GMLAN serial data wake up and the accessory wake up serial data circuits by applying voltage when the ignition key is in ACC, ON or START. The high speed GMLAN serial data wake up circuit wakes up the electronic brake control module (EBCM) for bus communication and the accessory wake up serial data circuit wakes up the engine control module (ECM) and transmission control module (TCM)
You need to take this to a qualified Technician who has the right tools to diagnose the problem which could be a bad BCM, bad ground , no vehicle power B+ going to it, open fuse ,open serial data circuit.

And AAn