No starter

Good morning.

The code is for a no communication with the PCM.

Does the check engine light come on with the key on?

Roy

DTC U0073 or U2100

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (See: Vehicle > Initial Inspection and Diagnostic Overview > Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (See: Vehicle > Initial Inspection and Diagnostic Overview > Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (See: Vehicle > Initial Inspection and Diagnostic Overview > Diagnostic Procedure Instructions) provides an overview of each diagnostic category.

DTC Descriptor
DTC U0073 00
- Control Module Communication Bus Off

DTC U0073 71
- ECU HS Bus Off

DTC U0073 72
- ECU LS Bus Off

DTC U2100 00
- Controller Area Network (CAN) Bus Communication

DTC U2100 47
- Controller Area Network (CAN) Bus Communication

Circuit/System Description

The serial data circuits are serial data buses are used to communicate information between the control modules. The serial data circuits also connect directly to the data link connector (DLC).

Conditions for Running the DTCs

* Supply voltage at the control modules are in the normal operating range.
* The vehicle power mode requires serial data communications.

Conditions for Setting the DTC

The control module setting the DTC has attempted to establish communications on the serial data circuits more than 3 times in 5 seconds.

Action Taken When the DTCs Sets

* The module suspends all message transmission.
* The module uses default values for all parameters received on the serial data circuits.
* In the TCM, DTC U0073 will cause the transmission to go into default gears.
* In the ECM and TCM, DTC U0073 will cause the malfunction indicator lamp (MIL) to illuminate.
* The module inhibits the setting of all other communication DTCs.

Conditions for Clearing the DTC

* The ECM/TCM modules turn OFF the MIL after 4 consecutive ignition cycles that the diagnostic runs and does not fail.
* A current DTC clears when the malfunction is no longer present.
* A history DTC clears when the control module ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

Circuit/System Verification

1. Refer to Data Link References (See: Information Bus > Initial Inspection and Diagnostic Overview > Data Link References) to determine which serial data system is used for a specific control module.
2. This DTC cannot be retrieved with a current status. Diagnosis is accomplished using the symptom Scan Tool Does Not Communicate with High Speed GMLAN Device (See: Information Bus > Symptom Related Diagnostic Procedures > Scan Tool Does Not Communicate with High Speed GMLAN Device) or Scan Tool Does Not Communicate with Low Speed GMLAN Device (See: Information Bus > Symptom Related Diagnostic Procedures > Scan Tool Does Not Communicate with Low Speed GMLAN Device).

That is because of the fault code. The fact is that the PCM is working but cannot communicate with any other modules.

You need someone with an advanced scan tool to see if they can access live data to do all the checks that I sent you. It could be a wiring issue or the PCM itself that has failed.

Roy