OBD communication fails NJ, DMV

Tiny
CHELAFISH
  • MEMBER
  • 2010 MAZDA 3
  • AUTOMATIC
  • 230,000 MILES
My car listed above failed to communicate with NJ DMV Computer. The mechanic performed the gateway system wire repair, and I went back to DMV and had the same communication failure.
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Wednesday, June 22nd, 2022 AT 8:49 AM

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Tiny
AL W
  • EXPERT
Hello. does your car have auto wipers and headlights? Just looking at the network diagram for your car right now. Do you know exactly which module he did the wire repair for, or did he just repair a wire splice somewhere? Any details will help, but I can already see where the problem might be. Also did he say if he couldn't communicate with any specific modules with his scan tools? I'm assuming at the DMV they only need to communicate with the engine computer to check for trouble codes that affect emissions.
And is your instrument cluster working, okay? Or ABS light on?

There are a couple small changes in the wiring diagram if you have Auto headlights and automatic wipers, that's why I'm asking.
It looks like the Body Control Module is going to be the Gateway to the engine computer (PCM), transmission computer (TCM) and the ehpas module. Thats all that is there after the BCM network.

https://www.2carpros.com/articles/can-scan-controller-area-network-easy
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Wednesday, June 22nd, 2022 AT 10:58 AM
Tiny
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  • MEMBER
I uploaded screenshots from the mechanic and DMV. I do not have auto wipers or headlights.
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Wednesday, June 22nd, 2022 AT 11:19 AM
Tiny
AL W
  • EXPERT
Okay, so if there were no communications at all from any module, there are a few possibilities. Is this something you want to check yourself? If so, do you own a basic multimeter?
So, the network can be down because of a specific module taking the network down. It can be one of the network wires has damaged insolation and is touching the frame or engine and shorting out. That would be a short to ground.
One of the network wires can be shorted to power (12volts), the network only averages about 2.5 volts in between messages. The two wires of the network can be shorted together.

On the form where it says Status, I see some system listed there. What is that the Status of? Because depending on what's working in your car right now, it can help determine where there might be a fault. For example, if your ABS light is on, Airbag light (SRS light), etc.
I'm assuming that the mechanic was able to establish communication before he gave the car back to you.
The Data Link Connector is where they hook up to for scan tool and DMV checks. In between the DLC and the Engine computer is the Body Control Module. But there are some checks you can do at the Data link connector(DLC) to see if the basics are there. 12volt power, Ground, and some voltage signals on the network. Do you have Keyless entry and Start system? And this is a 2.5 Liter engine?
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Wednesday, June 22nd, 2022 AT 11:34 AM
Tiny
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  • MEMBER
I don't have any lights on at the moment, and yes l do have a multimeter so I can try to test myself before going back to the mechanic.
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Wednesday, June 22nd, 2022 AT 1:01 PM
Tiny
AL W
  • EXPERT
Yes, there are some checks you can do. It's odd you have no warning lights on if communications were down, but it does depend on what is down. Unfortunately, we don't know what wires the mechanic messed with really. Below is the Data Link Connector. Not sure why they colored it like this and labelled it with letters but set your multimeter on DC 20 volts. With the key in the on position first. Just lightly touch the pins, don't shove the meter leads into the connector because you will spread the pins and no scan tool will ever have communication (also on a side note, which is something to check. If the female pins in the Data Link Connector are spread to far, a no comms condition can happen, and some aftermarket scan tools have been known to do this. So, it's worth checking. Maybe the mechanics scan tool has wider pins than the one at DMV, and that's causing the no comms. Maybe check them with a small pin so as not to spread them but still check that they are ok.) On to the voltage checks, touching the green "LG" pin (12v) and the other meter lead on the either of the black "B" pins (both Grounds), you should read battery power. Verify that you have 12volts touching both "B" pins (H and J).
The Pins labelled R and W are the High Speed CanBus network pins we're interested in. The GY and G Pins are for the medium speed network and control climate control, audio, information display, etc.
So, the Pin R, with the other meter lead on one of the B pins (ground). Run the car for this check. Pin R is the CAN L it will most likely average 2.5 volts, it might jump around between 1.5 volts and 2.5volts. The meter will average the voltage reading as best it can. But an average of 2.5 is better than 12 volt or 0 volts.
The W pin is the CAN H it will be about the same except 2.5 volts up to 3.5 volts.
When you're checking the pin tension at the data link connector, just because and don't short any pins to other pins. The LG pin will have 12 volts all the time, even with the key being off. And the other network pins will stay active until the car is locked and all the modules go to sleep (low power mode). But the pin fitment issue is a real concern. There was a Bulletin about this happening from other manufactures. It would explain why the mechanics scan tool might work but others don't.
Let me know what you find.
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Wednesday, June 22nd, 2022 AT 2:00 PM
Tiny
CHELAFISH
  • MEMBER
I have a keyless entry, but no remote start. I start the car with a key, and yes, it's 2.5 L.
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Wednesday, June 22nd, 2022 AT 10:13 PM
Tiny
AL W
  • EXPERT
Okay, do those checks, especially the tension of the DLC pins. It's a common problem when aftermarket scan tools are used, not dealership scan tools. The pins are different sizes. Just be very careful not to short any pins together, but you can find spread female pins at DLC.
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Wednesday, June 22nd, 2022 AT 10:56 PM
Tiny
AL W
  • EXPERT
Let us know what you find, we like to get feedback. Thanks.
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Thursday, June 23rd, 2022 AT 4:04 PM

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