Lbz GPCM delete

[ZeroGravity58]

For everyone that wants to delete the GPCM. I searched and didn't find much. Anyways while doing my head gaskets and unpinned and pulled everything out of the engine harness except the for CAN buss wiring. The GPCM on the LBZ has a 120ohm terminating resistor. I order a 2 way GT 150 J1939 terminating resistor and wired it in the engine harness. Truck runs and takes tunes just like it should. The glow plug light will stay on since nothing can communicate with the GPCM. I pulled the cluster and took a small drill bit and drilled the light out as I don't feel like staring at it. Just trying to help others out if you want to do the same.

 

[2004LB7]

Can't turn that off in the tune?

 

[ZeroGravity58]

No there is no way to turn off the light on the dash that I could figure out.

 

[2004LB7]

That sucks. I take it turning off all the codes along with zeroing out the on time for the plugs didn't help?

 

[ZeroGravity58]

All the codes can be turned off. The SES light is not on. The glowplug light is what stays on. It comes on and never goes off.

 

[LBZGPCM]

All the codes can be turned off. The SES light is not on. The glowplug light is what stays on. It comes on and never goes off.

OK, First Off....... ZeroGravity58, you know your stuff!
I have searched EVERYWHERE and at most, people think this and people think that about if its even possible to delete... YOU FRICKING DID IT...
Now, I NEED HELP!!!!! Please

Lets look at LBZ owners biggest problem with the GPCM, you can't buy them new and you cant find them used! I suspect my LBZ GPCM is not COMMUNICATING with the ECM (U0106) and Reduced Power Mode is the result. Reduced Power sets immediately after clearing codes and we have checked most everything else and feel it has to be bad GPCM.

So, what would be the most simple way to test if a resistor can complete this CAN buss communication issue?

What would I want to do to the GPCM wiring? And how to identify the correct wires? What to do with wires and how/where to put this 120ohm terminating resistor.

It also sounds like when I clear this problem, I NEED TO PUT MY TRUCK IN YOUR SHOP AND LET YOU GET AFTER IT......

THANKS

 

[juddski88]

OK, First Off....... ZeroGravity58, you know your stuff!
I have searched EVERYWHERE and at most, people think this and people think that about if its even possible to delete... YOU FRICKING DID IT...
Now, I NEED HELP!!!!! Please

Lets look at LBZ owners biggest problem with the GPCM, you can't buy them new and you cant find them used! I suspect my LBZ GPCM is not COMMUNICATING with the ECM (U0106) and Reduced Power Mode is the result. Reduced Power sets immediately after clearing codes and we have checked most everything else and feel it has to be bad GPCM.

So, what would be the most simple way to test if a resistor can complete this CAN buss communication issue?

What would I want to do to the GPCM wiring? And how to identify the correct wires? What to do with wires and how/where to put this 120ohm terminating resistor.

It also sounds like when I clear this problem, I NEED TO PUT MY TRUCK IN YOUR SHOP AND LET YOU GET AFTER IT......

THANKS

Have you tried following the diag procedure for communicating with the gpcm?

 

[ZeroGravity58]

I can get the part numbers I used for the resistor, I wired the resistor in but have since removed it when I cleaned up the harness. I haven't had any problems with or without the resistor with it taking tunes or running. You can leave the module in a retune the truck to remove the codes. If you delete the GPCM without tuning even with the resistor your gonna have the same code. I still have the U0106 code when you scan but it's a soft code. I don't recommend deleting glow plugs if it gets below freezing many days where you live or you travel much to colder climates. I have a working LBZ GPCM at home if you need one. Also check and make sure you have power at the module.

 

[LBZGPCM]

I can get the part numbers I used for the resistor, I wired the resistor in but have since removed it when I cleaned up the harness. I haven't had any problems with or without the resistor with it taking tunes or running. You can leave the module in a retune the truck to remove the codes. If you delete the GPCM without tuning even with the resistor your gonna have the same code. I still have the U0106 code when you scan but it's a soft code. I don't recommend deleting glow plugs if it gets below freezing many days where you live or you travel much to colder climates. I have a working LBZ GPCM at home if you need one. Also check and make sure you have power at the module.

Ok, sell me your working one....

 

[LBZGPCM]

Have you tried following the diag procedure for communicating with the gpcm?

I have not, does that take a Tech 2 to do?

 

[juddski88]

I have not, does that take a Tech 2 to do?

A good mdi2 clone is a couple hundred bucks, a good tech2 clone is a little more. Then you can get a short term subscription to techline for dealer level support. If you don't want to do that, we can help find a reputable shop nearby that can help you.
Service info and diagnostic procedures for free up to 50$ can only take you so far with a good multimeter and understanding of how the system is layerd out and how it works.

 

[LBZGPCM]

A good mdi2 clone is a couple hundred bucks, a good tech2 clone is a little more. Then you can get a short term subscription to techline for dealer level support. If you don't want to do that, we can help find a reputable shop nearby that can help you.
Service info and diagnostic procedures for free up to 50$ can only take you so far with a good multimeter and understanding of how the system is layerd out and how it works.

I think it would be smart to have someone who uses a Tech 2 often to do any programming, I have never touched one. I would be interested in what shop knows this stuff and who could program the module I hope to buy from ZeroGravity58.

Thanks for all the help!

 

[juddski88]

I think it would be smart to have someone who uses a Tech 2 often to do any programming, I have never touched one. I would be interested in what shop knows this stuff and who could program the module I hope to buy from ZeroGravity58.

Thanks for all the help!

If you buy the module from him, all you really need to do is transfer the fuel injector flow rate codes over from your ecm. Not an intensive process. But the reason I posted in this thread, is because you have not actually done enough diag to prove that the gpcm is the issue.

 

[LBZGPCM]

If you buy the module from him, all you really need to do is transfer the fuel injector flow rate codes over from your ecm. Not an intensive process. But the reason I posted in this thread, is because you have not actually done enough diag to prove that the gpcm is the issue.

I was able to check the Network Integrity with the pin diagram that DAVe3283 supplied, I measured the resistance at 120ohms.

CANBUS VOLTAGE TEST 2.7 high side - 2.3 low side

Any other tests you would suggest?

 

[juddski88]

I was able to check the Network Integrity with the pin diagram that DAVe3283 supplied, I measured the resistance at 120ohms.

CANBUS VOLTAGE TEST 2.7 high side - 2.3 low side

Any other tests you would suggest?

How and where did you measure the resistance?

 

[LBZGPCM]

How and where did you measure the resistance?

Pins 43,44 I checked the circuit with batteries disconnected and got 120ohms.

 

[juddski88]

Ok, so this is why having a schematic of the circuit and a diag procedure would be helpful to you. You would notice that many of the modules data comm circuits are in series, not parallel. So if you disconnect one in the middle of the "start" (DLC) and the "end(s)" (ECM and resistor in the chassis harness), you will see the result you are seeing. The GPCM is in series between the BCM and then the TCM and finally the ECM, which has the terminal resistor. If you take any of the modules between the DLC and the ECM out, you are effectively removing the terminal resistor and preventing communications on the bus as a whole. The truck still runs, therefore, you dont have an open or a bad short in the data circuits of the GPCM. It is possible the module just cant communicate anymore due to a board fault, but that is very very rare. It is most likely that a power or ground circuit to the gpcm is not as it should be. I am not saying that's what I believe it is, just that it is most likely based on odds, but you never know until you test it all out fully

 

[LBZGPCM]

Ok, so this is why having a schematic of the circuit and a diag procedure would be helpful to you. You would notice that many of the modules data comm circuits are in series, not parallel. So if you disconnect one in the middle of the "start" (DLC) and the "end(s)" (ECM and resistor in the chassis harness), you will see the result you are seeing. The GPCM is in series between the BCM and then the TCM and finally the ECM, which has the terminal resistor. If you take any of the modules between the DLC and the ECM out, you are effectively removing the terminal resistor and preventing communications on the bus as a whole. The truck still runs, therefore, you dont have an open or a bad short in the data circuits of the GPCM. It is possible the module just cant communicate anymore due to a board fault, but that is very very rare. It is most likely that a power or ground circuit to the gpcm is not as it should be. I am not saying that's what I believe it is, just that it is most likely based on odds, but you never know until you test it all out fully

Now I just need someone who understands all this to take a look at the truck. Scottsdale AZ

Do you think any harm could come from just installing another GPCM without copying the flow rates from another LBZ?

Thanks

 

[2004LB7]

Now I just need someone who understands all this to take a look at the truck. Scottsdale AZ

Do you think any harm could come from just installing another GPCM without copying the flow rates from another LBZ?

Thanks

It will set a code for mismatched injectors flow codes

 

[juddski88]

Here is a link to find a whole bunch of used GPCMs also...

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