So my car exhibit all the low battery symptom like christmas tree dash warning etc. Will not crank at all not even click. Using the on board diagnostic menu I get 11.4-11.6v when I probe the battery using multimeter it will show 12.3-12.6 volt and this is even with the battery fresh off the charger.

Last week I took and check and clean all the ground connection and still no dice. So this week's today I tackle the last possibble culprit...the ECU.









The reason for pulling the ECU is suspecting moisture making it go haywire since I saw some frozen droplets around the vincinity of the passenger side footwell when I am down there and read some post pointing to the same issue after searched the forum. All happen around after wet season like rain or snow etc.

Upon opened up the ECU I didn't see any moisture sign but still using wife's hairdryer to go over once using low heat setting. Will pick up electrical contact cleaner from Autozone to clean out the connector at the wire side in the next few days.

So this lead me to a question for you all, the ECU casing is not airtight seal and the gap is pretty substantial especially the front part, can I use tape to seal it up airtight or is the gap is needed for the ECU to vent the heat generated inside the board?

Thanks.

 

If the battery shows 12.3 (which is low anyway), and the car sees only 11.4 volts...the obvious would be a problem with the battery cables or a ground. What voltage do you see at the cigarette lighter? If it shows a volt less than the battery posts, then there is a connection issue. It should be within a couple hundreths of a volt of what the battery shows.

Personally, I have never had any luck restoring electronics that were shorted from water. I read about people who have...but I read about more that have not. If you didn't see any moisture, then I personally would move on to something else anyway. The ECU is pretty robust.

 

It looks like something chewed through your filter? Lots of leaves and ice up there; something living in there?

 

I will be rechecking the voltage again, went thru all the connection and it is clean and tight. forgot to use the cigaratte lighter as a cross check.

The ECU is very clean and have no sign of water or moisture at all. However ran across a post that leaking trans harness will also show about the same situation I have. Another one is something about the shifter electronic board that is just under the shiftgate and my gut feeling is gonna be one of the 2 instead of the ECU.

Wish me luck this Thursday but I doubt I have the luck.

 

Well some update. The car starts now and it is not the ECU. It is the shifter electronic board that are under the shifter and it sits directly under the parking brake actuation lever. All the works and effort waste just to figured out the connector just need to reseat and it went back to normal.

The black plug is one of the plug I just unplug and replug.



This bigger connector is the second one that I unplug and replug.



Now my interior looks no different then those car that's been sitting in the junkyard. Ran out of daylight today to put it back so I'll have to drive it as is for a week, can wait how is the reaction of coworkers see it tomorrow.

 

one quick thing u can check I know u checked the cables on the battery. Take off the negitive connection where it bolts to the body take some sand paper on bolth surfaces. I had a car that had that problem once. And it would keep the car from turning over.

 

Another update. After the fixed the car works fine for about 5 days and then back to the same problem again so it's been sitting for the past 3 weeks. Today I went ahead blindly and got a gallon of gasoline sitting on top of the hood with a lighter next to it and ready to burn the cat down if it doesn't start by the end of the day.

Last week the intrument cluster is out and plug and replug to hopefully cleaned the contact and still no dice. All these while when it happen it always pop a code P1638 when scan and from search it is always lead to the CANBUS network so all I need to find is all the connector and connection within the CANBUS system.

Dissasemble further into the whole area and sprayed electrical contact cleaner on the board to tried to cleaned out the rusted pin area although already checked connectivity and resistance which shows good contact.





That still produce no start and all the fault is still there and then saw this sitting down there and unplug and replug the 2 connectors to it.



This seems to do the tricked and the christmas tree lights on the dash doesn't light up anymore. This is only what shows on it now. Car starts 2 consecutive time with no symptoms of low battery voltage which always lights up the christmas tree on the dash and faulty messages and also locking the door lock.



Ran out of daylight and this is how it is sitting outside the house now...







Next week the fun part of putting everything together will commence and while everything still apart I will make some connection for the rear entertainment auxillary plug in and selector to the cupholder area while the center console is still apart to run my MP3 player.

PS: The gasoline and lighter part is just fictional and it didn't happen.

 

How old is your battery? You may be chasing ghosts here when it could be as simple as a failing battery.

 

Yes, a battery "fresh of the charger" means nothing. It will charge up and still be defective. Load testing and inductance testing will tell you 100%. If not that, it will be poor connections introducing high resistance and therefore voltage drops where you least expect them.

If it was me, I would put a high quality, brand new battery before doing *anything* else.

 

XJ8s MUST have a completely healthy battery and secure ground (earth) points.

 

Well guys, believe me, I only when thru all this trouble after I exhaust all the "easy step" which included the battery test/swap, grounding point cleaning etc.

 

from your invitaton to takea looka t your resolve on this area mine pale in to insignificance. Well done you and hope your glad yuo didnt use that gallon of gas and the lighter;_)