03 and up Ford 6.0 no comm

Robert from Newark Mobile Technician Posted   Latest  

I wanted to share a time saving tip that I figured out after numerous no start diagnostics on these vehicles. As a mobile tech I need to get in and out as fast as possible so I am always looking for ways to get the most amount of information, in the shortest amount of time, so I can be 100% accurate on my diagnostic. Everyone has their own methods and that's great as long as it's producing great results. So I have had a few 6.0 Ford diesels that I was called out to program a new pcm on that would not communicate. Many techs don't realize that on most vehicles the module needs to communicate before it can accept software. So you hook up IDS or whatever scan tool you are using and it won't communicate with the pcm. Or in the case of ids it simply won't let you get past the vehicle id screen. Here's what I have found that has not let me down yet. Hook up your dlc breakout box and scope 6&14. If CAN high and CAN low are sitting at ground, go out to the powertrain control module (front of left inner fender) and unplug the center connector. Now recheck for communication / CAN bus activity. If it now works then you can likely skip the time consuming task of verifying the integrity of the powers, grounds, CAN lines, and / or wake up circuits. Unplugging this middle pcm connector opens up the 5 volt reference circuit removing the short to ground the was killing communication. It appears there is a tie in between the ref circuit and the can transceiver inside of the pcm. The 5 volt power supply for the ref circuit must feed the can transceiver, which would explain why both are affected when there is a short to ground on the ref circuit. I've supplied a couple of pictures of the connector. If you are looking at the front of the pcm, the far left connector is mainly powers, grounds, can lines, sensors, and ref supply for the map, baro, and APP. The middle one is mainly 5 volt ref and engine sensors. The smaller of the three, on the right side is all transmission related. Something interesting that you might notice is that there is only one 5 volt ref wire leaving the middle connector that supplies ref power to most of the sensors and fan clutch. Finding the short will be the fun part. At least you will only have 5 minutes into it up to that point if this time saving method has helped you. 

" Success is the ability to go from failure to failure without losing your enthusiasm "

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Thomas from Saint Petersburg

 

Diagnostician
 

Great tip, and I love that final quote!

+1

Robert from Newark

 

Mobile Technician
 

Thank you! It's one it's one of my favorite quotes.

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Ben from Cartersville Ga

 

Service Manager
 

Great tip and your quote is spot on

+1

Ben from Cartersville Ga

 

Service Manager
 

could you give me part number on your breakout box thank you

0

Robert from Newark

 

Mobile Technician
 
+1

Ben from Cartersville Ga

 

Service Manager
 

Thank you

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Rick from Dracut

 

Technician
 

Thanks for the great tip, Robert.

+1

Adrean from Bakersfield

 

Diagnostician
 

Great tip!

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Michael from Holt

 

Diagnostician
 

Fantastic tip and yes finding its fun but not impossible as couple items come to mind that are typical failures on these. Thanks so much for sharing the knowledge

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Glen from Arthur

 

Technician
 

Isn't the fan clutch reference voltage on a 6.0L buffered 12 volt?

Did you happen to notice if the CEL was on in bulb check?

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Chris from Commack

 

Technical Support Specialist
 

It shows to be a 12v buffered power, but when shorted it will still take down the pcm.

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Chris from Commack

 

Technical Support Specialist
 

The diagram shows Vpwr which is typically 12v buffered power.

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Albin from Leavenworth

 

Diagnostician
 

Bob, this spring I had a 2014 F250 6.7 towed in as a no crank. The owner said he was close to home, several of the gauges quit working and several warning lights came on in the cluster. The engine continued to run normally. Once it was shut off, it would not crank again. When I hooked up my IDS, I couldn't get past the home screen.

I grabbed my Snap on scan tool, which let me comm with everything except the PCM. Here is where I made my mistake. I started unplugging things. :( Well, I wanted to find something quick. I did find several U codes for modules not communicating with the PCM.

The first and easiest module on the CAN bus is the PCM, so I unplugged it, and Walla, comm came back to the network. I should have used my DLC BOB and scoped the can lines. With the PCM plugged bacd in the engine cranked and ran properly. Two months later, the same vehicle was driven back to my shop with the same cluster symptoms. I did some pin fit checking on the center plug to the PCM and I found two pins not meeting the drag test. The vehicle owner opted to take it back to the dealer and let them worry about it, since it should have been under warranty.

+3

Chris from Commack

 

Technical Support Specialist
 

To get past the home screen with no PCM communication, when it says there is no communication with the PCM would you like to retry?, Click no and ignore all of the key prompts. Eventually (after 4-8 key cycles) it will prompt for tear tag or calibration information. Tear tag can be found on the PCM (4 digit code normally in largest letters) or in the Asbuilt menu from OASIS. Enter the tear tag information and then you will have full scan functionality to run network test and self-tests to determine what modules are offline.

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