2005 volvo xc90 will not stay running, it is giving a code of U0073 generic control module communication bus"a" off. .we have put in new crank sensor. the maf sensor is not the problem

https://repairpal.com/obd-ii-code-u0073-control-module-communication-bus-a-off

https://www.snapon.com/EN/US/Diagnostics/News-Center/CAN-Bus

https://www.obd-codes.com/u0073

What make ,model an year vehicle ? Can't help you without that .

Great. Now fix the right front wheel sensor c0040, coo73. Next the u2100 is a voltage issue. The DTC did not see enough voltage to the system. Check the battery and connections. Check charging system.

You'll need to get a good auto electrician to look at this. The codes suggest a failed ECU, the brain reading all the engine sensors. If this fails, the car is unusable as the ECU won't let the vehicle work.
Codes read as:
U0073 - Control Module Communication Bus "A" Off
U0100 - Lost Communication With ECM/PCM "A"
U0101 - Lost Communication with TCM
U0121 - Lost Communication With Anti-Lock Brake System
(ABS) Control Module
U0155 - Lost Communication With Instrument Panel
Cluster (IPC) Control Module
I have very little experience with gearboxes so I can't really help with the 3rd gear problem.

U0073 Control Module Communication Bus Off Digital Signal Processor REFER to Section 418-00 . U0073 Control Module Communication Bus A Off EATC Module REFER to Section 418-00 . U0073 Control Module Communication Bus A Off SJB REFER to Section 418-00 . U0073 Control Module Communication Bus A Off TCM (FNR5 Speed Transaxle) REFER to the Powertrain Control/Emissions Diagnosis (PC/ED) manual. U0073 Control Module Communication Bus A Off TCM (6 Speed Transaxle) REFER to the Powertrain Control/Emissions Diagnosis (PC/ED) manual.
Your best bet , take it to a qualified repair shop . You do not have the knowledge or diagnostic test equipment to diagnose this . Do you know what C.A.N. - controller area network is ?
Communications Network Vehicle communication utilizes both medium and high speed controller area network (CAN) communications. CAN is used for many modules to communicate with each other on a common network. CAN in-vehicle networking is a method for transferring data among distributed electronic modules via a serial data bus. Without serial networking, intermodule communication requires dedicated, point to point wiring resulting in bulky, expensive, complex, and difficult to install wiring harnesses. Applying a serial data network reduces the number of wires combining the signals on a single network. Information is sent to the individual control modules that control each function.
The vehicle has 2 module communication networks:

• Medium speed (MS) CAN
• High speed (HS) CAN

Both networks are connected to the data link connector (DLC). This makes diagnosis and testing of these systems easier by allowing one scan tool to be able to diagnose and control any module on both networks from one connector. The DLC can be found under the instrument panel between the steering column and the audio unit.

016 CAN Communications

P0020 - Intake Camshaft Position Actuator Circuit/Open (Bank 2) Description: See the description for DTC P0010. Possible Causes: See the possible causes for DTC P0010. Diagnostic Aids: See the diagnostic aids for DTC P0010. Application Key On Engine Off Key On Engine Running Continuous Memory All GO to Pinpoint Test HK .

U codes are communication codes . You won't be able to fix this , guaranteed . Your best bet would be to take it to a buick dealer .
The serial data circuit is the means by which the control modules in the vehicle communicate with each other. Once the scan tool is connected to the serial data circuit through the DLC, the scan tool can be used to monitor each module for diagnostic purposes and to check for diagnostic trouble codes (DTCs). When the ignition switch is in RUN, each control module communicating on the serial data circuit sends a state of health (SOH) message to ensure that the control module is operating properly. When a control module stops communicating on the serial data circuit, for example if the module loses power or ground, the SOH message it normally sends on the serial data circuit disappears. Other control modules on the serial data circuit, which expect to receive that SOH message, detect its absence; those control modules in turn sets a DTC associated with the loss of SOH of the non-communicating control module. The DTC is unique to the control module which is not communicating, for example, when the inflatable restraint sensing and diagnostic module (SDM) SOH message disappears, several modules set DTC U1088. Note: a loss of serial data communications DTC does not represent a failure of the module that set it.

U0073 00
Control Module Communication Bus A Off
U0073 71
ECU HS Bus Off
U0073 72
ECU LS Bus Off

There are 2 different communication networks on this vehicle: The class 2 network and the GMLAN network. The class 2 serial data circuit is the low speed link, and the GMLAN serial data circuit is the high speed link. Modules that need real time communications are attached to the high speed network. The engine control module (ECM) is the gateway between the networks. The purpose of the gateway is to transfer information from one network to another.

012 GM Class II Communications

001 Welcome to 20 Years of Communication Networks for Imports and Domestics

002 Introduction to Communications

016 CAN Communications

Disconnect batt see if it clears. Or unplug computr..clean connection pins...see if unit reboots. Dirty brake fluid can ruin abs module. To pinpoint du a datastream w a factory scantool and not at a dealer. Code readers dont give u numbrs for decision.

communication failure on CAN-Bus.
take it to the shop.
as in all cases, electrical
check all fuses first.
reseat the connectors to the transmission.
FSM
Trouble Code: u0073 Control Module Communication Bus Off
Trouble Code Conditions:
TCM fails to transmit and receive the data via CAN for specified time continuously.
Possible Causes:

• TCM
• circuits
• ECM

B1318 Safety restraint module supply below 9volts.
U0073 Can bus communication error.
Likely causes....Dead battery / charging problems or Wirng or supply to module or module fault.