GM

GM Repair Problems? Ask GM Repair Expert Now.

Ask an Expert,
Get an Answer ASAP!

GM

I Have a 2006 Duramax 6.6 . The problem I have is DTC code

Customer Question
UO100- ECM/PCM communication loss, low...
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: 7 years ago.Category: GM
Show More
Show Less
Ask Your Own GM Question
Answered in 3 hours by:
4/18/2010
GM Mechanic: Mark, ASE Certified Technician replied 7 years ago
Mark
Mark, ASE Certified Technician
Category: GM
Satisfied Customers: 847
Experience: 34+ yrs Dealership Exp. - Fully State & ASE Certified - GM Master & GM World Class Tech
Verified
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
Mark, ASE Certified Technician
Category: GM
Satisfied Customers: 847
Experience: 34+ yrs Dealership Exp. - Fully State & ASE Certified - GM Master & GM World Class Tech
Verified
Mark and 87 other GM Specialists are ready to help you
Ask your own question now
Ask Mark Your Own Question
Mark
Mark
Mark, ASE Certified Technician
Category: GM
Satisfied Customers: 847
847 Satisfied Customers
Experience: 34+ yrs Dealership Exp. - Fully State & ASE Certified - GM Master & GM World Class Tech

Mark is online now

A new question is answered every 9 seconds

How JustAnswer works:

  • Ask an ExpertExperts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional AnswerVia email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction GuaranteeRate the answer you receive.

JustAnswer in the News:

Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... Justanswer.com.
JustAnswer.com...has seen a spike since October in legal questions from readers about layoffs, unemployment and severance.
Web sites like justanswer.com/legal
...leave nothing to chance.
Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.
Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.
I will tell you that...the things you have to go through to be an Expert are quite rigorous.

What Customers are Saying:

I was having a terrible problem with the wheel bearings on my 98 Chevy Cavalier and I suspect that using this website saved me plenty of time and money.

Todd LRochester NY

Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help.

Mary C.Freshfield, Liverpool, UK

This expert is wonderful. They truly know what they are talking about, and they actually care about you. They really helped put my nerves at ease. Thank you so much!!!!

AlexLos Angeles, CA

Thank you for all your help. It is nice to know that this service is here for people like myself, who need answers fast and are not sure who to consult.

GPHesperia, CA

I couldn't be more satisfied! This is the site I will always come to when I need a second opinion.

JustinKernersville, NC

Just let me say that this encounter has been entirely professional and most helpful. I liked that I could ask additional questions and get answered in a very short turn around.

EstherWoodstock, NY

Thank you so much for taking your time and knowledge to support my concerns. Not only did you answer my questions, you even took it a step further with replying with more pertinent information I needed to know.

RobinElkton, Maryland

< Previous | Next >

Meet the Experts:

GM Tech (Cam)

GM Tech (Cam)

GMC Mechanic

5,792 satisfied customers

GM Grand Master Technician 2007. 14 years experience.

Gary

Gary

GMC Technician

1,537 satisfied customers

15 years gm master tech/15 years ASE master tech

car tech

car tech

ASE Certified Technician

449 satisfied customers

25 year master tech and shop owner

Chris (aka- Moose)

Chris (aka- Moose)

GMC Technician

211 satisfied customers

16 years of experience

Paul M ASE Master

Paul M ASE Master

ASE Master Tech

187 satisfied customers

ASE Master Tech 20+ Years

Anthony

Anthony

GMC Technician

489 satisfied customers

GM Certified

Amedee

Amedee

GMC Technician

455 satisfied customers

ASE certified tech with advanced level specialist. Wisconsin certified emissions state inspector

< Previous | Next >

Related GM Questions
Lose electric power when I us the plow. I'm thinking a bad
Lose electric power when I us the plow. I'm thinking a bad ground somewhere … read more
Chris (aka- Moose)
Chris (aka- Moose)
GMC Technician
Vocational, Technical or Trade School
211 satisfied customers
My 2001 GMC Sierra 4x4 with a 5.3 l motor starts and then
My 2001 GMC Sierra 4x4 with a 5.3 l motor starts and then immediately revs so high I have to shut it dow. … read more
David Craig
David Craig
OWNER/MECHANIC
Associates
4,403 satisfied customers
It cranks but won't start. Its getting fire but won't get no
yes its getting fire but won't get no connection..fuel supply working fine … read more
Gary
Gary
GMC Technician
Vocational, Technical or Trade Scho
1,537 satisfied customers
Hummer 2008 h3, cold weather 5 degrees, turn key on, all
Hummer 2008 h3, cold weather 5 degrees, turn key on, all lights come on and ready to start but turn key to start engine, eginee light stays on and i only here a click click click … read more
GM Tech (Cam)
GM Tech (Cam)
GMC Mechanic
Vocational, Technical or Trade Scho
5,792 satisfied customers
As I was driving along, the truck just died and will crank
As I was driving along, the truck just died and will crank but won't start … read more
GM Tech (Cam)
GM Tech (Cam)
GMC Mechanic
Vocational, Technical or Trade Scho
5,792 satisfied customers
I am installing a backup camera in my 2007 gmc 2500 and need
I am installing a backup camera in my 2007 gmc 2500 and need to know where to wire the monitor to the backup wiring in the cab … read more
Mechanic01
Mechanic01
1,700 satisfied customers
I just replaced the blower speed control for the second time
I just replaced the blower speed control for the second time in less than 6 months. I was testing the controls to be sure everything functions properly. As soon as I switch the to the face, the fan st… read more
GM Tech (Cam)
GM Tech (Cam)
GMC Mechanic
Vocational, Technical or Trade Scho
5,792 satisfied customers
06 hummer H2. Service 4WD. Switches flash when commanded. It
06 hummer H2. Service 4WD. Switches flash when commanded. … read more
Todd Audette
Todd Audette
Automotive Technician
Vocational High School
138 satisfied customers
My low beam lights will not turn on. Fuse is good and I have
fuse is good and I have used multiple bulbs, all have not turned on … read more
Todd Audette
Todd Audette
Automotive Technician
Vocational High School
138 satisfied customers
2005 avalanche and the car started and the emergency brake
2005 avalanche and the car started and the emergency brake light (brake was not pushed)came on and service 4 WD message. I shut the car off, unplugged positive side of battery for 5 minutes, cleared t… read more
GM Tech (Cam)
GM Tech (Cam)
GMC Mechanic
Vocational, Technical or Trade Scho
5,792 satisfied customers
My 2007 yukon denali just started today, the rear glass
Hello my 2007 yukon denali just started today, the rear glass access pops open and then the heated seats turn off, and the lights on the inside go dim, on and off. I shut the glass and when you hit th… read more
GM Tech (Cam)
GM Tech (Cam)
GMC Mechanic
Vocational, Technical or Trade Scho
5,792 satisfied customers
I have a Hummer H2 2003 model. I was running low on fuel and
Dave I have a Hummer H2 2003 model. I was running low on fuel and parked on hillside and believe fuel ran to front and uncovered fuel pickup. open door jumped out and left vechicle running and door op… read more
GM Tech (Cam)
GM Tech (Cam)
GMC Mechanic
Vocational, Technical or Trade Scho
5,792 satisfied customers
Smoke is comeing from my ac compressor.. 99 gmc jimmy. 4wd
Smoke is comeing from my ac compressor.. 99 gmc jimmy . 4wd v6 … read more
Mechanic01
Mechanic01
1,700 satisfied customers
My 04 3500 duramax is in limp mode has a code of p0202. No
my 04 3500 duramax is in limp mode has a code of p0202 … read more
TIM MOHR
TIM MOHR
SHOP OWNER
Master's Degree
8,037 satisfied customers
I have Chevrolet colorado 2016 engine 2.5 i need wirring
I have Chevrolet colorado 2016 engine 2.5 i need wirring diagram for powersteering and the ABS module i have no communication whith 2 module… read more
GM Tech (Cam)
GM Tech (Cam)
GMC Mechanic
Vocational, Technical or Trade Scho
5,792 satisfied customers
I have a 02 Astro van it's got the 4.3 Vortec and it started
I have a 02 Astro van it's got the 4.3 Vortec and it started missing when it's wet … read more
rpmdiag
rpmdiag
High school
7,273 satisfied customers
Still not getting any spark. Ecm has power, and good ground.
Still not getting any spark. Ecm has power, and good ground. Replaced ecm with one from a car that ran. Still no spark. What's wrong?… read more
David Craig
David Craig
OWNER/MECHANIC
Associates
4,403 satisfied customers
I have a 2007 GMC Yukon XL, when I try and start, it takes 2
I have a 2007 GMC Yukon XL, when I try and start, it takes 2 tries to get it to start. I have been told it's the fuel pump but it's been doin … read more
Chris (aka- Moose)
Chris (aka- Moose)
GMC Technician
Vocational, Technical or Trade School
211 satisfied customers
Disclaimer: Information in questions, answers, and other posts on this site ("Posts") comes from individual users, not JustAnswer; JustAnswer is not responsible for Posts. Posts are for general information, are not intended to substitute for informed professional advice (medical, legal, veterinary, financial, etc.), or to establish a professional-client relationship. The site and services are provided "as is" with no warranty or representations by JustAnswer regarding the qualifications of Experts. To see what credentials have been verified by a third-party service, please click on the "Verified" symbol in some Experts' profiles. JustAnswer is not intended or designed for EMERGENCY questions which should be directed immediately by telephone or in-person to qualified professionals.

Disclaimer: Information in questions, answers, and other posts on this site ("Posts") comes from individual users, not JustAnswer; JustAnswer is not responsible for Posts. Posts are for general information, are not intended to substitute for informed professional advice (medical, legal, veterinary, financial, etc.), or to establish a professional-client relationship. The site and services are provided "as is" with no warranty or representations by JustAnswer regarding the qualifications of Experts. To see what credentials have been verified by a third-party service, please click on the "Verified" symbol in some Experts' profiles. JustAnswer is not intended or designed for EMERGENCY questions which should be directed immediately by telephone or in-person to qualified professionals.

Show MoreShow Less

Ask Your Question

x