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· Registered
3 Posts
My 2500HD of 118K miles starting throwing network codes this week.
All stock...
The truck runs fine most of the day, then without warning the trans will start shifting at odd RPM's, power drops a bit... and the check engine light may or may not illuminate.
I'm getting:
U2104 CAN Bus Reset Counter Overrun
U2105 ECS Comm lost
U1800 FICM comm loss
U1152 HVAC Comm loss
U2106 TCS comm loss

I've reseated all appropriate fuses and cables.
I cannot locate corrective actions for the network errors.
Does AllData provide this type of info?

· Premium Member
9,509 Posts
Are the batteries the original ones? I have read that batteries going bad can cause really stupid things that you could be chasing for a while. It could be a PCM going out, but I haven't heard of anyone having this problem.

· Registered
10 Posts
All the codes are probably can bus related. Many of the on board ECUs are connected (and communicate with each other) by a single 2 wire data line... the can bus. If one of these ECUs goes bad, it can take down the can bus. Then none can communicate. That is how you would see so many comm codes. With other makes we find the culprit by disconnecting one ECU at a time until communication is restored... an "easy" answer to a complicated problem. But the catch is they aren't usually easy to get to. A buddy of mine told me how a BMW tech unplugged over 20 ECUs on a BMW before he found the guilty one!

· Registered
1 Posts
ALLDATA will have all the trouble codes for the truck listed in their database as well as the OEM diagnostic proceedures for each one. For the price it is a very nice tool to be able to have essentially the entire factory repair manual at your disposal. Having access to all the technical service bulletins issued by GM is a nice side benefit. I just went in and took a look to make sure for the U1152 HVAC code and the diagnostic proceedure is there with a step by step chart.

I think you will probably find it easier to use the diagnostic charts to find the issue instead of disconnecting modules until you find the guilty one.

DTC U1152

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message for state of health monitoring/node alive messages. A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. Once an identification number is learned by a module, it will monitor for that modules node alive message. Each module on the class 2 serial data circuit is required to send a Node Alive message every 2 seconds. When no message is detected from a learned identification number for 5 seconds, a DTC U1XXX. XXX is equal to the 3 digit identification number of the module.

When more than one loss of communication DTC is set in a single module or among multiple modules, diagnose the DTCs in the following order:

Current DTCs before history DTCs except as specified in the diagnostic tables.
The DTC which is reported the most times.
From the lowest number DTC to the highest number DTC.

Voltage supplied to the module is in the normal operating voltage range of 9-16 volts.
DTCs U1300, U1301 or U1305 do not have a current status.
The vehicle power mode requires serial data communication to occur.


IMPORTANT: The following steps must be completed before using the symptom tables:

Perform the Diagnostic System Check for the subsystem exhibiting the symptoms. The subsystem diagnostic system check will identify where to begin diagnosis of the data link communication system.
Review the system operation in order to familiarize yourself with the system functions. Visual/Physical Inspection
Inspect for aftermarket devices that could affect the operation of the serial data communications systems.
Inspect the easily accessible systems or visible system components for obvious damage or conditions that could cause the symptom.
Faulty electrical connections or wiring may be the cause of intermittent conditions.

Good luck


· Registered
3 Posts
Discussion Starter · #6 ·
Thanks for the tips guys! I replaced both batteries. One was only pushing 404CCA's. Still had the orig. problem.
Since I was leaving town and running out of time, I resulted to the dealer.. Tech found chaffed wire at the FICM bracket where a previous tech (previous owner) must had performed inj. service and forgot to secure the harness which was rubbing on the bracket. No more codes since.
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