P1698, alternator

Just thought I'd share, this is kind of a weird one. Searching the board shows this has thrown people for a loop before.

97 XJ, 4.0. It's been running fine. The first symptom was a clicking or popping noise through the speakers, even with the stereo off. About 30 miles after that started the check engine light turned on. About 40 miles after that the voltmeter in the cluster started fluctuating, then the check gauges light came on as the voltmeter dropped to zero. I drove back to the shop to find 13.5V on the battery and a P1698 code, a bus code for pcm-tcm communication. No other codes. The 1698 was a hard fault- it would pop right back up immediately after being cleared.

I checked out the alternator circuits, they were fine, replaced the alternator and all is well. It's really strange that this code would come up for a charging issue, especially 40-50 miles before the system quit charging. But there it is.

Maybe this will help somebody out in the future.

I'm not one to usually resurrect old threads, but being how mysterious the P1698 code can be I figured I'd share.

I just experienced the SAME EXACT scenario with my 97 4.0. Had been running great, no issues. Then noticed a bit of feedback in the stereo. The same day the check engine popped up with the P1698 code as I was leaving work (yeah I keep a scanner in the Jeep lol). Drove home from work ~45 miles and suddenly lost the the alternator just as JJacobs described.

I have 5-90's wiring and checked all connections to ensure proper connectivity. A new alternator solved the issue. Shop confirmed that the alternator was bad.