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Error codes P1698 and P1687

BDHershey

NAXJA Forum User
Location
Lexington, SC
Twice in the last two weeks the check engine light in my '99 XJ Sport (with 4wd, 4.0, and Automatic tran) has come on and then gone off after a day or so. I was in getting new tires at the Goodyear where my buddy works and he plugged it in to their diagnostic machine and got error codes:

P1698 - No transmission bus
and
P1687 - No Mic bus

the jeep has been running fine, trans shifting fine, and the speedometer and odometer working fine. What do these mean and any idea what need to be done to fix them? I searched here but didn't find what I was looking for.


-Hershey
 
Last edited:
ive been havin the same problems with mine. i jsut took all the connectors out of the tranny, cleaned the out, threw some di electric grease in there adn havent had them come back on yet
 
The 99 FSM lists the codes this way: 1687, "no MIC bus" no "CCD/J1850 messages" have been received from the instrument cluster. P1698 is the same n-bus failure from the Transmission controller. I'm guessing this means that when the system starts up it checks for feedback, and if it doesn't find the connection satisfactory it sets those codes.

Since problems with the connector to the instrument cluster are a common complaint with this vintage model, I'd start there, with cleaning and replugging the instrument cluster and the transmission control unit.
 
I had the A/C evaporator replaced a month or two ago at the dealership. I was told they would have to tear down the dash. Possible reason? Though it has just started. Where is the TCU located, I haven't found a reference to it in my Haynes either.

-Hershey
 
Update....

I think I found the TCU. On the center console stack in the drivers foot well? I saw it described somewhere else as about 4"x4" give or take. Silver. Aisin or something like that on it. That's what this looks like. Connections seemed firm. I didn't disconnect. If/when I do, what should I clean it with?

-Hershey
 
BDHershey said:
Update....

I think I found the TCU. On the center console stack in the drivers foot well? I saw it described somewhere else as about 4"x4" give or take. Silver. Aisin or something like that on it. That's what this looks like. Connections seemed firm. I didn't disconnect. If/when I do, what should I clean it with?

-Hershey

You can get non-flammable electrical contact cleaner in various places, including, at least in former times, Radio Shack, sold as TV tuner and control cleaner. That works pretty well usually. It might be sufficient just to unplug and replug the connector. No harm in trying it.

I don't have an automatic, so I don't know where the TCU is on a 99, but it will indeed be a little silver box that says "Aisin Warner" on it, so it looks as if you've found yours.
 
Update...

Light was off for about a week. But has now come back on. Disconnected/reconnected the TCU again and light is still on. Truck runs fine, and shifts fine, no problems there. But my wife and I switched rides for mileage reasons and am afraid that it may leave her stranded. Are there sources for new TCU's? Haven't had much luck on the internet other than some used ones. Any help is appreciated! Thanks guys!

-Hershey
 
Hey guys any suggestions on where to find a TCU or TCM? If I go to the salvage yard are they pretty interchangeable or do I need to look for another '99? Also I was reading somewhere else on here that the TPS and TCM work pretty close together and that sometimes the TPS can cause tranny probs. Also that the TPS doesn't like water here at all. THis all started to happen after a torrential downpour here a feww weeks ago. I was out in the middle of nowhere delivering cookie for a church ministry and the flooded dirt roads I had to travel got the engine compartment pretty wet. Again I have had no driveability probs of yet but the light comes on for several days, then is off for several, then back on, etc. Since we traded I don't want the wife stuck somewhere. Thanks again for any suggestions!

-Hershey
 
I just started getting the p1698 code as well as p1682 (voltage too low). After driving 7 hours through the rain. After parking at a rest stop for a while with the engine running to dry things out. My voltage came back up (from 9 to 14). Towards the end of the trip the tranny started slipping out of OD. I cleared the codes, cleaned the wire harness going to the PCM, and still had p1698 pop-up. Any advice before I bring it to a dealer with a better diagnostic tool then the one I keep in my trunk?

-1998 XJ 4.0L and Auto
 
I had the A/C evaporator replaced a month or two ago at the dealership. I was told they would have to tear down the dash. Possible reason? Though it has just started. Where is the TCU located, I haven't found a reference to it in my Haynes either.

-Hershey

Its located just above the gas pedal take the panel down under the steering wheel and look up to your right you will see it.
 
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