mchan68 Posted June 30, 2019 Share Posted June 30, 2019 Okay, this is a very interesting one. Unit is a 2014 F-550 tow truck 232K kms and high hours. Vehicle has had a drop in long block replaced about 6K kms ago. This DTC U0074 is a hard fault. Someone else just replaced the GPCM in an attempt to repair. I check it out. Go through the pinpoint test 'AF'. Seems to check out okay. The one thing I notice, all the circuit checks are contained within the 12A581 harness which includes the BJB as well connectors to both the driver side and passenger side interior connections. Finally got the harness replaced. The DTC is still present.🤬 I have ran a network test both, before and after harness replacement. And both times, the GPCM, NOx11 and NOx12 fail. The glow plugs indicator does not illuminate at KOEO or initial startup. But when I run the self-test, all the warning indicators including the glow plugs illuminate, so it is definitely confirmed that there's an with this system. I've even borrowed the GPCM out of my own truck to try, in order to rule out a faulty new GPCM. Running out of ideas. What are the chances of the PCM being the culprit for this mess? Do any of you guys have any suggestions? Quote Link to comment Share on other sites More sharing options...
tonybullitt Posted June 30, 2019 Share Posted June 30, 2019 Modified? Quote Link to comment Share on other sites More sharing options...
mchan68 Posted June 30, 2019 Author Share Posted June 30, 2019 24 minutes ago, tonybullitt said: Modified? Nope. Quote Link to comment Share on other sites More sharing options...
tonybullitt Posted July 1, 2019 Share Posted July 1, 2019 I usually have this on shorted out nox modules on modified trucks. I don't remember the fuse number that blows when shorted Quote Link to comment Share on other sites More sharing options...
tonybullitt Posted July 1, 2019 Share Posted July 1, 2019 Do you have power to glow plug module? I believe the nox modules and glow plug module are on a dedicated Network wire to pcm Quote Link to comment Share on other sites More sharing options...
tonybullitt Posted July 1, 2019 Share Posted July 1, 2019 I would check pin 6 at gpcm for power and pin 5 for ground. I know PPT AF never has u check but if no power and ground to gpcm it can't communicate. It's fuse f36 in bjb I was talking about in previous post that I have had blown on several modified trucks. Quote Link to comment Share on other sites More sharing options...
mchan68 Posted July 3, 2019 Author Share Posted July 3, 2019 Replacing NOx11 module fixed it. The first clue to this was by unplugging both NOx11 and NOx12 modules. After I did that, I immediately noticed the glow plug indicator light now illuminated at KOEO (when it didn't previously). After noticing that, I plugged back in NOx12, and still got the indicator at KOEO. Plugging back in NOx11 put it back to what it was doing before. So I "borrowed" the NOx11 module from my own truck to install temporarily, and by doing so was able to clear U0074 as well as bring GPCM, NOx11 and NOx12 back alive on the network. I was also finally able to get the glow plug monitoring system KOER self-test to complete and pass. Thanks for the help. Live and learn. 1 Quote Link to comment Share on other sites More sharing options...
8WA Sman Posted July 5, 2019 Share Posted July 5, 2019 Did you happen to ohm check the Can2 terminals on NOx11. I have never checked to see which modules have the terminating resistors on Can2 and I can't seem to find that info from Ford. Quote Link to comment Share on other sites More sharing options...
mchan68 Posted July 5, 2019 Author Share Posted July 5, 2019 Nope. But I do happen to remember the module had a very burned smell to it, when I removed it. Quote Link to comment Share on other sites More sharing options...
8WA Sman Posted July 6, 2019 Share Posted July 6, 2019 I checked a NOx11 today, I got 50k ohms. Quote Link to comment Share on other sites More sharing options...
tonybullitt Posted July 6, 2019 Share Posted July 6, 2019 When I have had nox modules blowing fuses they have smelled burnt also. Quote Link to comment Share on other sites More sharing options...
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