[s4bill]

Any shifting issues with the transmission or any dtc in the tcm? You should have a C0055 set in the ebcm too.

Google PIT3155B. It has all the diagnostic info you need to properly diag this. If the transmission is shifting fine, and the tcm doesn't have any dtcs, then you don't have a vehicle speed sensor (in the tail housing of the transfer case) issue.

So it appears you nailed it as far as the codes. Please try to stay with me as I am almost certain I am going to make this more difficult than it should be. As communicated earlier I have cleared the basic ODBC codes with my old scanner. That P0540 no longer exists and as others have mentioned it is probably not related. The speedometer will not work at all for a period of time and then the next time I start it will be completely normal and the Service Brake System message will disappear and then at some point it will return. If I hit a bump it will seem to affect the speedometer at times. Today I bought a new scanner from harbor freight. It was the nicest one they had without spending a $1000. It found the P0502 and I couldnt find anything else. Well that is because I didnt know how to use the scanner. I cleared the P0502 again and then realized there was a whole section for modules. I did a complete module scan and under the GLOBAL ODBC this P0502 shows Pending. Under ABS module,TA module and VSES module there is this C0055 code that you mention. They are showing as History Codes. In addition under the PPS and SIR there is a U1096 code that means "Lost communication with Instrument Cluster" There are no codes for the TCM or TCCM. I found a meter with has Hz listed under the DC Volts. I am going to read through that document you provided. Is there anything that you can tell from these codes that indicates anything? Thanks again for taking the time to respond. I hope you have a 4th of July.

 

[s4bill]

When my 06 did that it was the wire harness extension that GM uses for the 4x4s. My speedometer would jump around and go into limp. I changed the sensor first with no change and by accident found the problem with the wires in the connector on the extension. I was able to fix it without replacing as everything was closed when I found it but it's easy to change if that's it.

Thanks for getting back to me. I am going to check there first. Please excuse my ignorace. Where is this wire harness extension? Where does it come from? What does it connect to?

 

[ChevyTech77]

If you don’t have a code in the TCM then you most likely don’t have a VSS or VSS to TCM circuit issue. If you can read data with your scan tool, you can confirm this by checking for an accurate VSS signal/data in the TCM. Check in the ECM too. Sound like maybe you have an 812 circuit issue (VSS signal from TCM to ECM) or possibly a TCM issue. Stick with it. You’re almost there. 🍻

 

[s4bill]

If you don’t have a code in the TCM then you most likely don’t have a VSS or VSS to TCM circuit issue. If you can read data with your scan tool, you can confirm this by checking for an accurate VSS signal/data in the TCM. Check in the ECM too. Sound like maybe you have an 812 circuit issue (VSS signal from TCM to ECM) or possibly a TCM issue. Stick with it. You’re almost there. 🍻

I dont know if the scanner can read TCM data. It is a bidirectional scanner so it does some things. I saw live readings for all kinds of stuff but it appeared to be engine data. I will have to take another look at the scanner. My guess is that it does not. How would I find a wire diagram or some type of layout that showns where 812 circuit is located?

 

[ChevyTech77]

Check and see if the vss signal drops out in the ecm data when the concern is present.

Can't help with wiring diagrams, sorry.

 

[jdbuilders]

Thanks for getting back to me. I am going to check there first. Please excuse my ignorace. Where is this wire harness extension? Where does it come from? What does it connect to?

Normally the speed sensor is on the tail shaft of the transmission. When it's 4x4 it gets moved to the tail shaft of the transfer case. GM uses the same wiring harness for both situations and adds an extension for the 4x4. It will be on the driver's side of the drivetrain. You will see the connector for the extension about where the transfer case mounts to the transmission.

 

[Ron Nielson]

Attachment may be of some help.

 

[s4bill]

Check and see if the vss signal drops out in the ecm data when the concern is present.

Can't help with wiring diagrams, sorry.

The scanner has Powertrain live data section but it doesnt apper to have any TCM data. The only thing I could find was vehicle speed which I assume is being pulled from the ECM? The vehicle was warmed up and when it is at that state the speedometer barely works at all alot of the time. What I did notice is that the vehicle speed was zero in the ecm when the speedo was showing zero. This vehicle spped would show the actual speed at times and it matched was the waze app on my phone was showing for vehicle speed. It would literally flash a speed and go right back to 0. So yes, if I understand correctly the vss signal is dropping out of the ecm when the concern is present. I think I am going to invest in a nicer scanner that can read live data on everything. If the TCM was showing live VSS data that was solid and accurate, it would suggest that there is a problem between the TCM and ECM?

 

[s4bill]

Attachment may be of some help.

Thanks!

 

[ChevyTech77]

The scanner has Powertrain live data section but it doesnt apper to have any TCM data. The only thing I could find was vehicle speed which I assume is being pulled from the ECM? The vehicle was warmed up and when it is at that state the speedometer barely works at all alot of the time. What I did notice is that the vehicle speed was zero in the ecm when the speedo was showing zero. This vehicle spped would show the actual speed at times and it matched was the waze app on my phone was showing for vehicle speed. It would literally flash a speed and go right back to 0. So yes, if I understand correctly the vss signal is dropping out of the ecm when the concern is present. I think I am going to invest in a nicer scanner that can read live data on everything. If the TCM was showing live VSS data that was solid and accurate, it would suggest that there is a problem between the TCM and ECM?

Sorry yes, it is labeled as vehicle speed in the data list.

On the bold - Yes, exactly.

 

[07mydmax]

Just throwing this out there. My truck had the same messages "Service brake system" the brake light on the cluster lit up, and the speedometer would jump all over the place. Something had let go in my transfer case, tailshaft would move up and down pretty easy, and it wouldn't hold a tail shaft seal. I knew I needed a new Transfer case anyway, so I swapped it out and all has been well ever since. I think what happens is the front ABS sensors read different than what the tailshaft sensor was reading and causes the speedometer to go haywire.

 

[s4bill]

When my 06 did that it was the wire harness extension that GM uses for the 4x4s. My speedometer would jump around and go into limp. I changed the sensor first with no change and by accident found the problem with the wires in the connector on the extension. I was able to fix it without replacing as everything was closed when I found it but it's easy to change if that's it.

I found this extension wire. I did not notice any tears or rips. what exactly was wrong with the wire? Was it the wire or the connector?

Sorry yes, it is labeled as vehicle speed in the data list.

On the bold - Yes, exactly.

I got a scanner that stated it would show it and it has a whole section for TCM and TCCM but vss is listed nowhere in either of these modules. Could it possibly listed as something else?

 

[jdbuilders]

On the extension wire if I remember right it had a break in one of the wires at the connector. I would check continuity and wiggle the wires while checking. I know it's just one of the possibilities.

 

[s4bill]

When my 06 did that it was the wire harness extension that GM uses for the 4x4s. My speedometer would jump around and go into limp. I changed the sensor first with no change and by accident found the problem with the wires in the connector on the extension. I was able to fix it without replacing as everything was closed when I found it but it's easy to change if that's it.

Did you have any shifting issues? Was it only the speedometer that had issues?

 

[s4bill]

Sorry yes, it is labeled as vehicle speed in the data list.

On the bold - Yes, exactly.

I took it to a shop where the owner had 2 chevy's in the driveway and had the GM tech 2 scanner. He said there is no live data for the TCM or TCCM for my model year. He told me to clean all of the connectors and put dieletric grease on them. I am doing that now and then doing it for the extension cable.

If that doesnt work, I am going to do a check for continuity.

I wonder if this could be a bad TCM? Would they fail on something like this?

 

[Ron Nielson]

I think what happens is the front ABS sensors read different than what the tailshaft sensor was reading and causes the speedometer to go haywire.

Mu guess is that this is your problem.

 

[s4bill]

Mu guess is that this is your problem.

What is the solution if that is the problem? How do I check it?

 

[jdbuilders]

Did you have any shifting issues? Was it only the speedometer that had issues?

It would go into limp mode. That's when I started carrying my scanner with me so I could clear the codes and continue on until I found the issue. Mine seemed to act up more when on a rough gravel road or in rain where it would get the connector wet.

 

[ChevyTech77]

I took it to a shop where the owner had 2 chevy's in the driveway and had the GM tech 2 scanner. He said there is no live data for the TCM or TCCM for my model year. He told me to clean all of the connectors and put dieletric grease on them. I am doing that now and then doing it for the extension cable.

If that doesnt work, I am going to do a check for continuity.

I wonder if this could be a bad TCM? Would they fail on something like this?

Could be.

You need to follow the PI I posted back at the beginning of this and check for voltage, if the scan tool data isn't available.

 

[s4bill]

Could be.

You need to follow the PI I posted back at the beginning of this and check for voltage, if the scan tool data isn't available.

I plan on doing that. However I am having a difficult time determine which pins and wires are for the circuit. I see the circuit numbers mentioned but I cant seem to find a wiring diagram. I think I am going to post something in the electrical section asking specifically if someone has the pin assignments for the TCM connector and ECM connectors.

I did take that extension wire from the rear vss and checked it for continuity and it seemed fine. I was looking through the drawer of test lights and such an remembered I had a cable tracker from HF. I disconnected the connector from the VSS and put the transmitter on one of the pins and was able to get a signal at the wire going into the TCM. However I get no signal at the wires going into the ECM. I did this for both pins of the connector and the produced the same result.

Should there be continuity from the VSS through the TCM to the ECM?
You mentioned that it appears to be a problem with the TCM or from The TCM to the ECM. It seems you might be right.

It looks like wires route under the fuse box?

I am going to attack that tomorrow especially if I can determine which wires and pins to check for the circuit.