I just bought a PA state 03 f250 from a auction. I took it to the garage for inspection and emissions. (I'm told state vehicles do not require emissions.) When they hooked it up for emissions test, it send I failed reason signal loss. They checked all the fuses which were fine. they tried to hook up a handheld scanner and it comes up saying communication error. when you move the wires behind it the scanner will try to work but the same message comes up. The wires do look like they are not soldered together (like ends are twisted together) and electrical taped. The garage send they don't know what to do and I'm to try and find someone who does then bring it back for inspection. What could cause this, where or how can I fix this issue??

  • Welcome to Motor Vehicle Maintenance & Repair! Commented May 8, 2023 at 13:58

1 Answer 1


If you think you're having a wiring issue, I'd suggest taking the data link connector (DLC) plug down and examining the wiring there. I doubt it's a soldering issue. More likely, one of the pins in the DLC is not making the connection. Since there's only five pins which should be active for an OBDII link: CAN-high (pin 6); CAN-low (pin 14); chassis-ground (pin 4); signal-ground (pin 5); power (pin 16). You can test the two grounds with a multimeter on continuity mode. You can test power using a multimeter using DC voltage mode. If these are good, you'll need to see what the deal is with the two signal wires. If these are not good, you should be able to provide these without issue from which ever source (ground for grounds; power for power). If all of them are cut and "twisted together" (as I think you might be suggesting), you'll need to find the same colored wires coming out of the ECU and reconnect them correctly to the DLC. Usually, if someone has cut the wires like I'm thinking might have happened, the "other end" of them can't be too far away. No clue why someone would butcher the OBDII harness, even in the case you're suggesting, but realistically, anything is possible.

You can read more about the DLC and the OBDII connection at this site.

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