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Pete, Auto Service Technician
Category: Chevy
Satisfied Customers: 27935
Experience:  14 years GM dealer Technician.
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Pcm fuse blows immediately. Can't even plug in all the way.

Customer Question

pcm b fuse blows immediately. Can't even plug in all the way. No dash lights on speedo cluster. Won't communicate with scanner. 03 duramax lb7
JA: Sometimes things that you think will be really complicated end up being easy to fix with a Chevy. The Chevy Mechanic I'm going to connect you with knows all the tricks and shortcuts. Tell me a bit more about what's going on so he can help you best. Are you hoping to fix this yourself?
Customer: Batteries died. Charged both up, about 2 months old. Had dash lights but no glow plug light. Now no lights on cluster. Starter has not even clicked. Started up and idled for 15 minutes about a month ago to recharge batteries with no issues. Have tried disconnecting batteries for 1/2 hour to reset computer, no power to ecm fuse and pcm b keeps blowing.
JA: Cars do make very odd noises -- They help the mechanics figure out what's wrong. They are terrific with my old Grand Cherokee. Is there anything else important you think the Chevy Mechanic should know about your Chevy?
Customer: no
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Submitted: 1 year ago.
Category: Chevy
Expert:  Pete replied 1 year ago.

Hi my name is ***** ***** I will be happy to assist with this today.In some cases I may need more info to assist better.I apologize for any delay.

Is anything after market wired into the vehicle at all right before this issue occurred or to try and correct this issue?

Let me know so we can continue,thanks Pete.

Customer: replied 1 year ago.
No. Stock except trailer brake installed in 03.
Expert:  Pete replied 1 year ago.

O.k.,The PCM B fuse energizes the EDU relay and when this relay is energized it powers the ECMRPV and EDU fuses.So these fuses will not have power until the PCM B fuse fault is corrected.

For some odd reason the diagram is trying to tell me the PCM B fuse powers the fuel pump relay for a diesel engine and your model shouldnt use this relay.Double check in your under hood fuse panel to see if this relay is installed and if it is remove it and see if the fuse still shorts out and let me know.

The PCM B feeds the ECM (engine control module) as well here.If the engine control module has an internal electrical short in it this will occur and the ecm would need replaced.If there is a short in the wiring leading from the PCM B fuse to the engine control module this will occur as well and the wiring would need traced and inspected and repaired.If there is a short in the wiring leading from the PCM B fuse to the EDU relay this will also occur and the wiring would need repaired.

With this fuse being blown this will cause all of the issues you see here.You will need to locate the short by removing the edu relay to see if the relay is the cause needing replaced,removing the fuel pump relay (if equipped) to see if this relay is the cause needing replaced,or checking the wiring inside the fuse box running from the pcm b fuse to the edu and fuel pump relay for any shorts needing repaired,check the wiring from the pcm b fuse to the ecm to see if any wiring is at fault needing repaired.If all of these are o.k.and the short still continues then the ecm needs replaced.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

Customer: replied 1 year ago.
Removed F/PMP fuse, and still blows fuse. Was that the right one?
Expert:  Pete replied 1 year ago.

It would be labled Fpump relay or fuel pump relay and is square and large in shape,its not a fuse but a relay instead.I dont think your model has this although my diagram says your diesel does I havent seen one in a diesel myself.

Expert:  Pete replied 1 year ago.

I suspect the short is in the edu relay or wiring to the ecm or the ecm itself needing replaced.This will have to be checked/tested further to pinpoint and repair the fault here.

Let me know if you need anything else and feel free to rate my help here.

Thanks Pete