Scotty, I have a 2010 Ford edge all wheel drive 167,000 miles and for the most part has been running good no major issues. I received a emission notice from the state and went to the testing facility thinking no big deal. I was shocked when I was told I failed do to no communication with there device. I took my vehicle to my mechanic and he hooked up his scanner and got a reading no problem. Went back and same thing. Went to a different mechanic, his scanner also worked and no issues with the vehicle. Went to a different testing facility and failed again😖. Â This vehicle had a drivers side air bag recall so I scheduled with ford and while I was there paid for them to test the plug and provide documentation that all is good on my end. The finale test was a failure also and Iâm forced to pay for an extension for my vehicle tags. Any idea whatâs going on or have you heard of this before? Fords Equipment is all brand new, what the hellâs going on!
So everybody's scanners can communicate through the DLC except the government's scanner. That's a clue because they don't do things like normal people.
Let's look at a DLC (Data Link Connector) pinout.
Since everyone else can power up their scanners you know that there's battery power on Pin 16. Everyone else can communicate with the Networks so you know that there isn't a module or a terminating resistor dragging the network down.
That leaves the Grounds. Pins 4 and 5.
What if everyone's scanners are grabbing the Chassis Ground on Pin 4 to power their scanners but the govt is using the Signal Ground on Pin 5 (Clean Ground from the computer) to power theirs and there's a problem with that Ground?
This can be tested with an $8 multimeter from Harbor Freight or Amazon/ebay.
I'll post a video of a guy using Pin 16 as a Power source and checking the Grounds on Pins 4 and 5 using a multimeter. And it's a good starting point but it appears he's doing the voltage test with Key ON, engine OFF. I'd do the test with the engine running because the government guys are going to try to communicate with the computer that way and a lot of things can mess with those Grounds (especially the Pin 5 Ground from the computer) with the engine running.Â
And even with a cheap multimeter, testing Pin 5, IF you see those voltages fluctuate well above battery voltage (12.5 volts + or -) to over 16 volts and then drop below battery voltage then there's a problem in that Ground circuit. ((maybe a crummy Ground connection on an ignition coil)). The govt's scanner won't accept that voltage fluctuation.
So here's that video. It's not a Ford but the Power and Grounds are on the same DLC Pins.Â
https://youtu.be/myPt6WT4Rtw?t=248
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Interesting, Jack. Have you seen scanners that do this?
Technically speaking, using signal ground to power a device seems to me like exceptionally poor electrical design practice. "Signal" ground usually indicates high impedance circuit, and running power through it usually means distorting your signal in the best case, and at worst loading multiple amps through it leads to frying sensitive circuits.
Chassis ground (it's actually called "Scan tool power ground" in my documentation) should be a low impedance path directly to battery/generator negative capable of handing several watts of power.
well, it seems that in practice, automotive engineers have ignored this, and decided chassis ground was good enough for signals, and they've just tied both pins to the same grounding point on my vehicle. I guess the OBD protocols must be robust enough to handle interference from ground loops.
Frankly, I spent some time considering this issue and this is all I could come up with
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You have to consider this: "Where does the computer get its Ground to provide a ""Signal Ground?"" It gets it from a Computer Ground to chassis and there's a lot of stuff that can mess with that
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Anyway, it seems that the other scanners are using Pin 16 for Power and are able to communicate with the networks
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So how can this be?
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The guy went to some independent mechanics who I assume have high dollar scanners. He went to the dealer with "a dealer level" scanner
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They were able to not only Power Up their scanners but could access, through the DLC connector, the communication networks.
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You say using Pin 5 as a Ground for a scanner doesn't make sense. I agree.
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That's why I prefaced my response by pointing out he's dealing with a state gov't
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These drivers in these smog/emissions testing states are dealing with testing equipment that are made to prevent drivers from "trying to beat the system," they aren't made to diagnose problems with the owner's cars and I wouldn't be a bit surprised if their equipment is grabbing the Ground directly from the computer because all they want to know is what the computer is seeing
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Now I've been here long enough for everyone to know that I never pretend to have the answers for a guy having automotive issues 1,000 miles away from me
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I just point them to a testing procedure that I'd use to rule out ((or in)) my concerns
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In this case, after the guy spent probably hundreds of dollars between the dealer and independent mechanics, I'm just suggesting to him what I'd do. I'd assume that these guys are telling him, "My scanner has no problem connecting to your DLC " and they aren't testing both of the Grounds
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For the price of an $8 multimeter, I'd test those Pin 4 & 5 Grounds on the DLC connector with the car running
I agree. It only takes a minute to check.