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Mark
Mark, ASE Certified Technician
Category: GM
Satisfied Customers: 840
Experience:  34+ yrs Dealership Exp. - Fully State & ASE Certified - GM Master & GM World Class Tech
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I Have a 2006 Duramax 6.6 . The problem I have is DTC code

Resolved Question:

I Have a 2006 Duramax 6.6 . The problem I have is DTC code UO100- ECM/PCM communication loss, low voltage reference detected. PO700 something to do with transmission. ABS/ BRAKE fault light on, fuel gauge goes from full to empty after 20 seconds of running, Max speed is about 15 mph and bad idle. Ck'd all ground leads, ck'd batteries and replaced fuel filters and still no luck !! Do I have a bad ECM ?
Submitted: 4 years ago.
Category: GM
Expert:  Mark replied 4 years ago.
Greetings, my name is Mark.

You really have several issues going on here. Your "U" code is a lack of communication to your ECM.

You then go on to describe several other issues that may or may not be related. The low voltage, the 700 trans code, the ABS issue, and your fuel gage.

Like I said, this all may or may not be related. We replace a lot of instrument cluster for electronics issues. The ABS issue could be wheel speed sensors or something else. And your trans has its own computer module.

Personally though, I would address the "U" code first. The communication to your "Engine Control Module". At this point, that should take precedence over the other. That is most likely your reason for your "reduced power mode".

I am not sure how you want to handle this. I don't know you personally. In your question you mention nothing about what you have done already or what has been done to the vehicle. When all this started and why. I will just start out with giving you a starting point on your "U" code.

Below I have included the diagnostic flow chart for at least looking at some areas to see if you have any issues. You really should have a GM Tech II scanner to read data, and you should have a good DVOM. (Digital Volt Ohm Meter) You should have a good general knowledge of electronics and understand how to read wiring schematics.

If all your power and grounds are intact and all readings are with-in specs, YES, you could have a bad ECM. I can count on one hand the amount of ECM I have replaced. If you do indeed have a bad ECM, you will then need to have it programmed, and only a dealership can do that.

If you just wanted an opinion as to what to do, I would take your truck to a GM dealership that has a good diesel tech. You may spend more time and money chasing a problem than if you let someone who knows what to look for.

Hope this helps you get started. Let me know how if there's anything else you need or want. I will help you in anyway I can. If you don't like what I have to offer, I can refer you to another tech.

Thanks and take care,
Mark




DTC U0100-U02FF (Diesel Engine)

Circuit Description

Modules connected to the high speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits. The messages are supervised and also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. Each message contains the identification number of the transmitter module. A module with a high speed GMLAN serial data circuits malfunction or which loses power during the current ignition cycle will have a Loss of Communication DTC set by other modules that depend on information from that failed module. If any of the high speed GMLAN circuits are shorted to battery voltage, ground or between them, no communication is possible on high speed GMLAN serial data bus, and a DTC U0073 is set.

DTC Descriptors

This diagnostic procedure supports the following DTCs:

DTC U0100 Lost Communication With Engine Control Module (ECM)
DTC U0101 Lost Communication With Transmission Control Module (TCM)
DTC U0106 Lost Communication With Glow Plug Control Module (GPCM)

Conditions for Running the DTCs

Voltage supplied to the modules is in the normal operating voltage range.
The engine is running.

Conditions for Setting the DTC

A supervised periodic message that includes the transmitter module availability has not been received.

Action Taken When the DTC Sets

The module uses a default value for the missing parameter.
The malfunction indicator lamp (MIL) will illuminate on the second consecutive ignition cycle that the diagnostic runs and fails, for the type B DTCs. For a detailed description about DTC types, refer to Diagnostic Trouble Code (DTC) Type Definitions for the 6.6L (LLY) engine.

Conditions for Clearing the MIL/DTC

The MIL/DTC clearing depends on DTC type. For information about DTC types, refer to Diagnostic Trouble Code (DTC) Types for the 6.6L (LLY) engine.

DTC type B
- The MIL clears after 3 ignition cycles when the malfunction is no longer present.
- 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.
DTC type C
- 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

A poor connection at the inoperative module may cause this code to set.
An improperly powered module may cause this code to set.

Test Description

The numbers below refer to the step numbers on the diagnostic table:

  1. The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.

Step

Action

Yes

No

Schematic Reference: Data Link Connector Schematics

Connector End View Reference: Master Electrical Component List

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

Important: Use the DTC descriptor list in order to determine which module is not communicating on high speed GMLAN serial data bus.

  1. Turn the ignition ON, with the engine OFF.
  2. Test the following circuits of the module that is not communicating on high speed GMLAN serial data bus for an open or a short to ground:
The battery positive voltage input circuits
The battery positive voltage output circuits
The ignition voltage input circuits
The ignition voltage output circuits
The switched battery positive voltage circuits

Refer to the following:

Control Module References for the applicable schematic
Circuit Testing
Wiring Repairs

Did you find and correct the condition?

Go to Step 8

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Test the ground circuits of the module that is not communicating on high speed GMLAN serial data bus for an open.

Refer to the following:

Control Module References for the applicable schematic
Circuit Testing
Wiring Repairs

Did you find and correct the condition?

Go to Step 8

Go to Step 4

4

Test the high speed GMLAN serial data circuits of the module that is not communicating on high speed GMLAN serial data bus for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 8

Go to Step 5

5

Inspect the harness connectors of the module that is not communicating on high speed GMLAN serial data bus for poor connections and terminal tension at the following circuits:

The battery positive voltage input circuits
The battery positive voltage output circuits
The ignition voltage input circuits
The ignition voltage output circuits
The switched battery positive voltage supply circuits
The ground circuits
The high speed GMLAN serial data circuits

Refer to the following:

Control Module References for the applicable schematic
Testing for Intermittent Conditions and Poor Connections
Connector Repairs

Did you find and correct the condition?

Go to Step 8

Go to Step 6

6

Replace the module that is not communicating on high speed GMLAN serial data bus. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 7

--

7

  1. Install a scan tool.
  2. Turn ON the ignition with the engine OFF.
  3. Select the Display DTCs function for the module which was not communicating.

Does the scan tool display any DTCs which do not begin with a "U"?

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 8

8

Select the Display DTCs function for the modules which had the Loss of Communications DTC set.

Does the scan tool display any DTCs which do not begin with a "U"?

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 9

9

  1. Use the scan tool in order to clear the DTCs.
  2. Continue diagnosing or clearing the DTCs until all the modules have been diagnosed and all the DTCs have been cleared.

Did you complete the action?

System OK

--



Power, Ground, DLC, and Splice Pack SP205


Object Number:(NNN) NNN-NNNN Size: FS

High Speed GM LAN Serial Data 8.1L and Diesel


Object Number:(NNN) NNN-NNNN Size: FS
Mark, ASE Certified Technician
Category: GM
Satisfied Customers: 840
Experience: 34+ yrs Dealership Exp. - Fully State & ASE Certified - GM Master & GM World Class Tech
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