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P1698 - 2000 XJ Classic

daveIT

NAXJA Forum User
Location
Backwoods, PA
Tranny light came on on dash the other day. My ODB-II scanner showed P1698. Looks like you get that code when there is no communication from the TCM.

It still seemed to be shifting fine...I was about 10 miles from home and running up and down hills on the way and didn't notice anything weird. Coincidentally (???) I just had it in the garage for tires, alignment and and free oil change. I was wondering if the garage somehow knocked something loose so I unplugged the TCU harness and plugged it back in.

Tranny fluid was changed a little under 2 years ago before I drove across country. I usually do that every 30K, so still have a little while. Levels are fine. I reset the code, and it didn't come back on on the 12-mile trip to work, but it came back on when I went out for lunch. I also noticed that the speedo needle was randomly bouncing around, but no pattern to it with the shifts or anything.

Looks like TCMs are ~$35-75 on eBay and my dad has a few junker XJs at his house...just not sure how interchangeable they are year-wise or what years my dad has. I think one is a 98 or 99 and the others are older. Anything else I should check into? Thanks!
 
Verify that the Pink Serial Communication Interface (SCI) wire is not open between the Diagnostic Link Connector (DLC) and the TCM. Verify that it is not grounded out either. Repair wiring as needed.

Test the alternator output. Low voltage can trigger a P1698.

Replace the TCM if the wiring is OK and there is still no communication.

P1698 Potential Causes:
Scan Tool Conflict
TCM
Wiring

Confirmed P1698 fixes

2-3 Shift Soliniod Wiring
Shift Solenoid
New Alternator
 
I figured since the fluid levels were good, the fluid looked good and it was shifting right, that I'd just wait until the weekend to screw with it. On the way home today, the CHECK GAUGES light comes on. I look over at the alternator gauge and it's at 9. I think I found my problem. :) Of course it couldn't break the other weekend when it was nice and warm out...
 
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