[Dispatch20]

Earlier this summer I bought the 1996 Service Manual OBD2 Supplement for $20 shipped on Ebay. I wanted to see what it said about the CEL P1702 code, and any debugging steps. See attached pics for the only 2 pages on this (although it also has the OBD2 updated wire diagrams which is always helpful).

Just like in my recent experience, it takes 2 trips to make the CEL go on. The 1st trip stores a "pending" 1702 code, and then the 2nd trip will turn on the CEL for the code. How the car defines a "trip" is interesting to me. It seems to follow the OBD2 drive cycle rules where the car must be below a certain temperature and then perform some level of driving before it will register the pending/actual 1702 code. I suspect this is why my brief drives around my neighborhood would never create a CEL code (even with the entire TCU disconnected).

The P1702 debugging steps in the tech manual just look for a short or open circuit. But they take the measurements relative to chassis ground, so I think my theory above probably won't help anything.

A second thought I have is that my Arduino starts outputting the signal in the ACCESSORY key position and the actual TCU outputs it in the ON position. I may be remembering this incorrectly, so I definitely need to double check that. I want to make sure that prematurely sending the pattern (i.e. in Accessory instead of On) isn't screwing something up here.

If I really can't get this method to work, then it's time to do a 5MT swap and try leaving the TCU installed and fooling it with load resistors (per the recommendation a few posts up). To be honest, I don't recall why people disconnect the TCU when doing a 5MT swap in the 1st place. Perhaps the ECU gets unhappy if the TCU sends the ECU a torque cut signal when it thinks it is shifting. Or maybe if the TCU doesn't sense proper A/B/C solenoids, it permanently causes a torque cut or some sort of limp mode. I don't think a code P1702 would be thrown, though. (Just capturing some random thoughts for now). FYI - I know people with 5MTs have sometimes had to override the torque cut signal into the ECU to prevent some stalling issues during shifting. Something about the torque cut signal disconnected/floating causing problems for the ECU.

Lastly - Yes, I do have a post on the SVX Nation Facebook page. It doesn't get a lot of interest, and I find this forum page an easier way to capture ideas, pictures, and links.

(One more thought - I should log what the TCU outputs in this ECU serial datastream when the tranny bulkhead harnesses are completely disconnected. I imagine this has to put out a different pattern than I've previously seen. If it doesn't, then what is the point of this new TCU serial data stream? I can speculate that it's required per OBD2 regulations to have the TCU->ECU signal but I really don't know. Subaru calls it a "diagnosis" signal. Since you can already talk directly to the TCU via SSM2 for diagnostics, I don't know what this new signal really does. Maybe it can capture freeze frame data in the ECU for certain tranny faults?)