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Discussion Starter #1
I didnt know which forum to choose.

2006 Durmax 2500 LT3 Crew Cab

I was driving on the highway at highway speed in 4 wheel high as you would expect.

Out of nowhere, the speedometer start jumping and the service brake system error message appeared. The speedometer would jump back and forth or sit a zero for a brief second and then jump back up. Since then it seems that if it sits, the code and message will disappear once I restart it. It seems that it will not occur again until the truck warms up.

I dont think the service engine light came on initially. It was just the brake and abs light. Now the service engine light is on and I have 2 codes.
I have a P0502 which appears to be related to this. In addition, I now have a P0540. Could this be related? Is it more likely to be a coincidence?

I saw a thread about pump rub. I saw a thread about wiring.

I am going to climb under the truck tomorrow.

Are there any suggestions where to start to trouble shoot this?
Is this pump rub obvious under visual inspection?

As always, any help is greatly appreciated.
 

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I don't think these 2 are related. See the attachment and
Also see
 

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Discussion Starter #3
I don't think these 2 are related. See the attachment and
Also see
Thanks for responding.

The speedomter is not working at all now. I cleared the codes and drove the truck. The P0502 is back but the P0540 is not. I imagine it probably still a problem but I am going to focus on the p0502 for now.

I dont have the GM scanner. I have an ODBC scanner I paid $100 a long time ago.

It mentioned raising the back of the vehicle and putting the vehicle in gear. That is not very practical for me. Is that truly necessary. It mentions doing an ohm test. I am going to start there I guess.
 

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Wait. First off. Why are you driving on the highway, at highway speed, in 4high?

Could be a wheel hub/ wheel speed sensor that went bad.
 

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Discussion Starter #5
Wait. First off. Why are you driving on the highway, at highway speed, in 4high?

Could be a wheel hub/ wheel speed sensor that went bad.
That was a typo. I was reading a thread about this happening in 4 LO. That is a good catch. It was in 2W LO. Thanks for pointing that out
 

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Discussion Starter #6
That was a typo. I was reading a thread about this happening in 4 LO. That is a good catch. It was in 2W LO. Thanks for pointing that out
OMG I am a mess. It was 2 W High. It was what it was supposed to be for normal driving.
 

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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.
 

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Any shifting issues with the transmission or any dtc in the tcm? Your code reader isn't reading the right dtc because a dmax controller (ecm) shouldn't set a P0502. P150C is what a dmax ecm should set for a missing vehicle speed sensor (vss) signal. You should have a C0055 set in the ebcm too. Make sure you're measuring the resistance up at the tcm. Lots of issues with the twisted pair of vss circuits getting cut/chaffed causing this. You can read ac voltage on these same circuits up at the tcm as well as long as you can find a way to spin the rear wheels fast enough by hand. That's usually really hard to do on an Allison equipped truck.
There isnt any noticeable shifting prolems and now the speedomter does not move at all. The only thing is this code that shouldnt be and the Service Brake System message. Are there any videos showing how to to do this diagnostic? I am not an idiot. At least I hope not. Just helpful if I am see someone do it. For example do you remove the connector at the TCM and check for resistance across 2 pins?
 

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There isnt any noticeable shifting prolems and now the speedomter does not move at all. The only thing is this code that shouldnt be and the Service Brake System message. Are there any videos showing how to to do this diagnostic? I am not an idiot. At least I hope not. Just helpful if I am see someone do it. For example do you remove the connector at the TCM and check for resistance across 2 pins?
Read my updated post.
 

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Discussion Starter #10
Read my updated post.
I googled PIT3155B and I can only find one pdf file. This appears to be it. How do you check the voltage with the vehicle moving? I like your signature. I have done a fair amount of troubleshooting in my life but I feel like a real amateur right about now.

On vehicles equipped with the Allison LCT1000 Automatic Transmission, the VSS signal is sent to the
Transmission Control Module (TCM) via Circuits 821 and 822.
9/2/2017 #PIT3155B: Allison LCT1000 No Shift Speedometer Erratic/Inop P0721 C0237 P0500 C0055 - (Mar 7, 2007) • 2003 Chevrolet Silverado K 4WD …
MotoLogic 2/2
The signal from the VSS to the TCM is an A/C signal that produces approximately 28-34 HZ per 1 mile per
hour. This signal can be checked using a Fluke 87 (DVM) set on the A/C voltage scale with hertz function
activated and connecting leads to Circuit 821 and 822.
The TCM converts the VSS signal from an A/C sign wave to a digital wave. The TCM sends out
approximately 4.5 volts on Circuit 400 to the PCM/ECM. With the vehicle stopped, the DVM will read
approximately 4.5 volts on circuit 400, but once the vehicle begins to move the voltage will drop to near 0
volts. To check the voltage with the DVM with the vehicle moving, the min/max function should be set to 1
ms, the max should be 4.5 volt and the minimum should be -4.5 volts. The reason the reading goes
negative is because the TCM converts the A/C signal from the VSS to the exact digital wave, therefore
when checking the HZ signal on circuit 400 the fluke meter can be set on the A/C or D/C signal with hertz
mode active. Circuit 400 can be checked by backing out the terminal at the ECM/PCM connector and
placing the red lead of the meter to Circuit 400 and the black lead to ground. The signal from the TCM on
circuit 400 will be the same HZ reading as the VSS approximately 28-34 HZ per 1 mile per hour.
The vehicle speed signal to the IPC, radio, cruise control module, and body control is provide by the
ECM/PCM on Circuit 817.
Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited
is resolved without completing every step, the remaining steps do not need to be performed.
 

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I googled PIT3155B and I can only find one pdf file. This appears to be it. How do you check the voltage with the vehicle moving? I like your signature. I have done a fair amount of troubleshooting in my life but I feel like a real amateur right about now.

On vehicles equipped with the Allison LCT1000 Automatic Transmission, the VSS signal is sent to the
Transmission Control Module (TCM) via Circuits 821 and 822.
9/2/2017 #PIT3155B: Allison LCT1000 No Shift Speedometer Erratic/Inop P0721 C0237 P0500 C0055 - (Mar 7, 2007) • 2003 Chevrolet Silverado K 4WD …
MotoLogic 2/2
The signal from the VSS to the TCM is an A/C signal that produces approximately 28-34 HZ per 1 mile per
hour. This signal can be checked using a Fluke 87 (DVM) set on the A/C voltage scale with hertz function
activated and connecting leads to Circuit 821 and 822.
The TCM converts the VSS signal from an A/C sign wave to a digital wave. The TCM sends out
approximately 4.5 volts on Circuit 400 to the PCM/ECM. With the vehicle stopped, the DVM will read
approximately 4.5 volts on circuit 400, but once the vehicle begins to move the voltage will drop to near 0
volts. To check the voltage with the DVM with the vehicle moving, the min/max function should be set to 1
ms, the max should be 4.5 volt and the minimum should be -4.5 volts. The reason the reading goes
negative is because the TCM converts the A/C signal from the VSS to the exact digital wave, therefore
when checking the HZ signal on circuit 400 the fluke meter can be set on the A/C or D/C signal with hertz
mode active. Circuit 400 can be checked by backing out the terminal at the ECM/PCM connector and
placing the red lead of the meter to Circuit 400 and the black lead to ground. The signal from the TCM on
circuit 400 will be the same HZ reading as the VSS approximately 28-34 HZ per 1 mile per hour.
The vehicle speed signal to the IPC, radio, cruise control module, and body control is provide by the
ECM/PCM on Circuit 817.
Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited
is resolved without completing every step, the remaining steps do not need to be performed.
You can't check it very easily, with a dvom, while the vehicle is moving. The PDF you found/posted again, has all the information that you need. This isn't super easy diag unless you've done electrical diag for a long time and have been properly trained. A scan tool that can read all of the tcm and ecm data would be helpful too. Not trying to be a jerk, just trying to help.
 

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Discussion Starter #12
You can't check it very easily, with a dvom, while the vehicle is moving. The PDF you found/posted again, has all the information that you need. This isn't super easy diag unless you've done electrical diag for a long time and have been properly trained. A scan tool that can read all of the tcm and ecm data would be helpful too. Not trying to be a jerk, just trying to help.
I appreciate you taking the time to respond. I have always considered getting a decent scan tool. I have a 2011 Forester as well and an 80's Porsche (I dont believe the Porsche has an ODBC connection) The question is can I use something like the BLue Driver LSB2 to pull tcm and ecm data? Do I need something GM specific like the GM Tech 2 scanner? I dont want to drop a couple grand in a scanner but if I can get something that will work with both vehicles and do abs and transmission stuff, I would consider spending more than what the ios/android scanners cost.
 

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I didnt know which forum to choose.

2006 Durmax 2500 LT3 Crew Cab

I was driving on the highway at highway speed in 4 wheel high as you would expect.

Out of nowhere, the speedometer start jumping and the service brake system error message appeared. The speedometer would jump back and forth or sit a zero for a brief second and then jump back up. Since then it seems that if it sits, the code and message will disappear once I restart it. It seems that it will not occur again until the truck warms up.

I dont think the service engine light came on initially. It was just the brake and abs light. Now the service engine light is on and I have 2 codes.
I have a P0502 which appears to be related to this. In addition, I now have a P0540. Could this be related? Is it more likely to be a coincidence?

I saw a thread about pump rub. I saw a thread about wiring.

I am going to climb under the truck tomorrow.

Are there any suggestions where to start to trouble shoot this?
Is this pump rub obvious under visual inspection?

As always, any help is greatly appreciated.
It could be your instrument cluster gauges are going bad. Ours started out with the fuel gauge jumping around, then the oil pressure gauge went bonkers and made us think we were out of oil. We replaced it last year. This is a common problem with the Duramax diesels and GM recalled a bunch of them, but our 03 was too old. I found a rebuilt one on Ebay for less than $300 and our local mechanic put it in for us. They say they're not hard to install, but my husband didn't want to try it. They basically unplug underneath the dash, after you pop off the trim around the gauges.
 

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Discussion Starter #17
It could be your instrument cluster gauges are going bad. Ours started out with the fuel gauge jumping around, then the oil pressure gauge went bonkers and made us think we were out of oil. We replaced it last year. This is a common problem with the Duramax diesels and GM recalled a bunch of them, but our 03 was too old. I found a rebuilt one on Ebay for less than $300 and our local mechanic put it in for us. They say they're not hard to install, but my husband didn't want to try it. They basically unplug underneath the dash, after you pop off the trim around the gauges.
Did it cause a check engine light? If so, did you receive any codes or service messages?
 

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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.
 
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