Possible causes
- Faulty Engine control Module (ECM)
- Engine control Module(ECM) harness is open or shorted
- Engine control Module (ECM) cicuit poor electricl connection
- Low battery voltage
Help with Possible causes What does this mean?
Possible symptoms
- Engine Light ON (or Service Engine Soon Warning Light)
P1698 Jeep Description
Engine control Module (ECM) unable to communicate with Transmission Control Module (TCM)



Read more: http://engine-codes.com/p1698_jeep.html#ixzz3Fm1PWXRV

my voltage meter is acting really odd and bounching around and even dropping down to 9 but i had the alternator tested and it tested good but he said the diods could be bad even if it tests good. so where do i go from here?

 

Clean your grounds. Read cruiser's tips.

Also I'd be refreshing your connections as well, also a tip of his. Contact cleaner - spray the crap out of the ecm and tcm harness connections, whatever you can get to - if you see a ton of corrosion inside the connectors, that may be a big part of the problem, and you can see if you can get sandpaper and fix them up a bit.

These are just the first steps.

Also, I'm assuming the battery was also tested/known to be good?

 

The dude has a 1998 XJ, Cruiser's tips pertain to Realnuts XJ's.

 

I saw that, but are grounds not still an issue? At least harness connector cleaning would be relevant with the newer ones, no? If I got that code with any vehicle I'd be starting with harness connector refreshing or at least checking them.

Figured cleaning grounds would be a good tip for any and all xj's - I suppose not?

 

1698 is very elusive. Generally limited to 1997 XJ's.

Most possible cause is the TCM.

Try the manual shift test.

Access te TCM by removing the trim panel and knee blocker from under the steering column. The TCM is to the right of the steering column and is a small silver module. Remove the connector from the TCM then do the manual shift test. It will determine if it's a mechanical problem in the trans or an elctrical control problem.

With the TCM disconnected, note the operation of the voltmeter.

Do this and get back.

AW4 MANUAL SHIFTING TEST (FSM Procedures)

(1) This test determines if problem is related to mechanical or electrical component.

(2) Stop engine and disconnect transmission control module.

(3) Road test vehicle. Shift transmission into each gear range. Transmission should operate as follows:

• lock in Park
• back up in Reverse
• not move in Neutral
• provide first gear only with shift lever in 1–2 position
• operate in third gear only with shift lever in 3 position
• operate in overdrive fourth gear in D position

(4) If transmission operates as described, proceed to next step. However, if forward gear ranges were difficult to distinguish (all feel the same), or vehicle would not back up, refer to diagnosis charts. Do not perform stall or time lag tests.

CAUTION: Do not over speed the engine during the next test step. Ease off the throttle and allow the vehicle to slow before downshifting.

(5) Continue road test. Manually downshift transmission from D to 3, and from 3 to 1–2 position. Then manually upshift transmission through forward ranges again.

 

Thanks again Ken, I've learned a lot from your posts.

 

It's always the first step in chasing down odd problems. Clean/secure all engine bay grounds. No exceptions.

 

thats guys, i put in a new alternator and that seems to do the trick but havnt test drove it yet just fired it up

 

Nice man, let us know though - it doesn't just help us learn, it helps people that find these posts (which happens a LOT more than people realize)

I just got a new alt but turned out I don't really need it, but will put it in when Spring comes for the hell of it.

 

everything seems to be running right now