548chevelle

Last week when I started the car I had a dozen messages, Service traction control, service active handling, service fuel system, service alarm system, etc, Three gauges weren't working - fuel, engine temp and oil pressure. Voltmeter, tach and speedo were working. The car seemed to run ok so I drove several miles to my destination. When I got there I turned the engine off, waited a few minutes and restarted it. Everything was now ok except for the MIL light. When I got home I pulled the code - U0073. Looked it up and it is a CAN bus problem. An open which could be a connector problem or a short. What I need is a diagram showing where any CAN bus connectors are located. I've driven the car a couple times since and I just want to be a step ahead before the problem comes back.

Bill Dearborn

This could have been caused by a low battery voltage. This code can't be seen on a standard OBD II Scanner. You need a Tech 2 with a Candi Module to see this code. I don't know if you have the description of what the code means. Here it is from the factory service manual.

DTC U0073 or U2100
Diagnostic Instructions
• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
• Review Strategy Based Diagnosis for an overview of the diagnostic approach.
• Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors
DTC U0073: Controller Area Network (CAN) Bus Communication
DTC U2100: Controller Area Network (CAN) Bus Communication

Circuit Description
The GMLAN serial data circuits are controller area network (CAN) high and/or low speed serial data buses used to communicate information between the control modules. Typical data transmission speeds must be high enough to ensure that a required real-time response is maintained. There are two different types of GMLAN serial data circuits, the High speed 2-wire circuit and Low speed single wire circuit. The GMLAN serial data circuits also communicate directly to the data link connector (DLC). Messages are interpreted by the externally connected CANdi module which acts as a transceiver for the scan tool.

Modules connected to the GMLAN serial data circuits monitor communications during normal vehicle operation, where operation information is exchanged among the modules. All the modules on the GMLAN networks, maintain a transmit error counter (TEC) and a receive error counter (REC). The counter values increase with detected errors and will decrease with error-free messages.

Conditions for Running the DTC
• Supply voltage to the modules are in the normal operating range.
• The vehicle is in the RUN power mode.

Conditions for Setting the DTC
The module setting the DTC has attempted to establish communications on the GMLAN circuits for more than 7 times.

Action Taken When the DTC Sets
• The module suspends all message transmission.
• The module uses default values for all parameters received on the serial data circuits.
• The module inhibits the setting of all other communication DTCs.

Conditions for Clearing the DTC
• A current DTC clears when the malfunction is no longer present.
• A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Diagnostic Aids
This DTC cannot be retrieved with a current status. Diagnosis of a current DTC is accomplished via Scan Tool Does Not Communicate with High Speed GMLAN Device . Refer to Data Link References for the correct procedure for the specific module(s) and the busses they use to communicate.

The GM LAN connects the VCIM (OnStar module), the BCM, the ECM, the ESC and the Automatic Transmission Module. The BCM is the bus master. Here is a copy of the schematic for the manual transmission version.




To check the LAN for problems in the connectors you need to go to the connectors for each of the modules on the LAN. An open will be easy to find a short will be almost impossible to find unless there is visual evidence of damage somewhere.

What year Z06 do you have? The VCIM on the 06-09 models is located under the passenger seat. On the 10 and newer models it is located forward of the glove compartment above the BCM.

If you have trouble determining where the signals are in the various connectors send me a PM and I will see if I can gather the info in a word document and email it to you.

Bill

548chevelle

I use an OBDlink dongle and the OBDlink app on my Android tablet. It showed the U0073 code and also what to look for as a problem. I knew all that. What I need is a diagram showing where the connectors are located so I can check them. Also I doubt it's a battery problem. I've had a lithium battery for almost a year. It's normal voltage is a few tenths higher -13.4v and it cranks the engine like a mf-er. The car is an '11.

pielet97

Any progress?? I have the exact same issue on my 2007!

phipp85

Did you plug anything into the data link connector? I had this code pop up when I plugged in my aim solo DL at the track once.

pielet97

Not me, all stock with the exception of a mild to wild type relay.

Landru

Be darned sure to check 2 connectors in fuse pit under passenger seat,
make sure they're tight & secure.
IIRC they're large & blue.
Especially important to check this if there're often passengers.

Downward foot pressure thru flimsy cover results in connectors flexing ever so slightly. Opens galore. DIC goes nuts.
Been reported here more than once.

It's a cheap quick check, make certain these two connectors are seated. If it's the issue members w/ problem fashioned a shim supporting weight & away from connectors.

pielet97

Mine has never happened with a passenger and I just completed a 2 day HPDE with an instructor and never got the faults.....

phipp85

Did you ever figure out the issue?

pielet97

So I've gone 2 weeks, knock on wood, without any lights. I cleaned/sanded the grounds, unplugged the connectors near the remote oil res and moved the mild to wild ground to a legit ground. The grounds I cleaned are driver rear wheel, both front top engine compartment, passenger front door ground and the frame ground to the block. I also took the battery terminals off and ensured they were super tight.

pielet97

Well, it's back. U2100, U0073. This sucks, What should be the next move?

pielet97

To close my issue, I installed a new BCM and had the dealer reprogram, problem solved to this day.