OBDII stopped connecting in 2007 Subaru conv- advice on tracing?

[flipcorp]

My '88 Syncro with a 2007 2.5 Subaru H4 engine stopped displaying to my Scanguage II reader.

I diagnosed this initially as a corroded Rj45 connector between the gauge and the OBDII connecter under the bench seat, and replaced the cat-5 wiring end-to end.

However now neither the ScanGuage or my OBDII reader fully connects.

The OBDII reader can read the VIN and show some codes, but that's it. The ScanGuage just says "connecting" despite trying all the protocols.

The one code the OBDII reader appears to show is "P0600" - Serial Communication Link. But that could be normal, I've never looked at it before.

I have traced the OBDII to the ECU - verified CAN low and CAN high, and ground, V+ but then I am stuck.

What is the minimum required connections for this setup to make the OBD2 connection?

thanks!
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'88 Syncro
'65 Triumph Spitfire
'12 Suzuki
'79 Vespa

[MarkWard]

Have you tried your scan gauge in another vehicle? I have a spare harness so if needed I can move it to another vehicle. Verify it works before you start pulling your hair out. This will bump your thread.

[flipcorp]

I hadn't tried it in another car, but just did (2018 Audi), works great. So there is likely a single wire that I need to locate that provides signal. But where to start...
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'88 Syncro
'65 Triumph Spitfire
'12 Suzuki
'79 Vespa

[jlrftype7]

Power and Ground terminals, make sure the Ground for the Diagnostic Connector is good, and you have power for the needed pin as well.
You can google your donor vehicle probably to see what the original pins were, but the few that are Federally Mandated don't change from vehicle to vehicle. Manufs are allowed some leeway on other pins like a LIN BUS/private Comms line.
I always have to look up what pin is supposed to be what value, I don't keep that info in my head.
Pin 16, should be battery voltage, make sure your battery isn't low, just in case it's at 12.0 volts or going lower
Pins 4 and 5, are Grounds
Pins 3 and 11 probably are the Medium Speed Can Bus Pins, close to 2 volts, one will read slightly higher than the other
Pins 6 and 14 could be your High Speed Can Bus Pins, voltage should be a bit higher than on the Medium Speed Can Bus Pins[ closer to 2.8v for Positive Pin, and lower for the HS negative Pin/wire] , but with just an Engine ECU, I don't know if Subaru had their ECU on the HS or the Medium Speed side for Comms.
Anyway, it's hopefully helpful for you
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'68 Westy- my first VW and vehicle/Bus- long gone.- sold it to a traveling Swiss couple....
'67 Type 3 Fastback, my 2nd car- gone
'69 Semi-Auto Stick Shift Beetle-gone
2017 MINI Coopers, our current DDs
‘84 Tin Top - Hilga....Auto

[valvecovergasket]

for those of us that are visual learners

[jlrftype7]

[jlrftype7]

https://www.amazon.com/Tuansheng-Breakout-Protocol...mp;hvnetw=

This is one example of what's out there. There are so many more choices than just a few years ago it seems for these types of boxes. And the Price has gotten lower as well.
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'68 Westy- my first VW and vehicle/Bus- long gone.- sold it to a traveling Swiss couple....
'67 Type 3 Fastback, my 2nd car- gone
'69 Semi-Auto Stick Shift Beetle-gone
2017 MINI Coopers, our current DDs
‘84 Tin Top - Hilga....Auto