Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
Hi there...I am new to ScannerDanner.com, but recently have watched a bunch of his YouTube vids trying to resolve my "No Comm" (U0100) issue with my 2009 Mercedes ML350. While I am a pretty decent mechanic (I only work on my own corral of cars), this is the first time I have had to try to diagnose an electrical/computer issue.
For starters, and maybe obviously, when I turn the key, I get a no-crank, no-start. I have jumperd the starter, and it energizes, but that is about as far as my knowledge base takes me so far. I have checked the 5V ref and I am good there...though I doubted myself so I checked multiple sensors to make sure (5V at all checked sensor points).
OK...so I guess my initial questions are this: If I am getting a "No Com", but I have a good 5V ref, I am assuming that i don't have a short to ground issue (right?), and that my ECU is good (right?). So now what? I checked my CAN Bus initially (as my first step) and all was ok there. I do have some fuse issues in that several (critical) fuses are not blown, but not energized (such as Fuse 122 for the Starter and ME-SFI {ME} Control Unit, and FUSE 57 for the Fuel Pump, and a few others). And I have acquired a full set of wiring diagrams for the vehicle (which is the first time I have ever needed to read wiring diragrams...so still seems Greek to me).
I work on my own cars because I truly like to...and have for about 40 years (I was previously an Air Force Jet Mech, so in my head I feel like I can work on anything! But maybe not so in reality). So here I am, and old dog looking for a new trick and I am not ready to surrender and tow this thing to the dealership!
Thanks so much for your reply! My apologies for my slow acknowledgement...the day you replied, I had actually wound-up fracturing my hip, so this is the first time I am logging back in. I will follow your guidance and post my findings at the first possibility. I do like this car and I am looking forward to seeing it come back to life!
