2000 986S electrics

[Anser]

Long story short.
Last fall on a drive, engine died. All lights on dash on.
Towed it home and found the fuse for the DME and Immobilizer blew.
Replaced and restarted. Idled without issue for 5 minutes or so.
During the test drive it was fine until 3-4K RPM. Above that the fuse popped.
New fuse and got it home.
Cleaned and reseated every connector I could get to, including DME, Immobilizer and all engine sensors. MAF sensor and intake was spotless.
Next test drive it still was ok under 3-4K RPM, but this time the engine cut out momentarily and CEL flashed, but returned to normal under said RPM.
back in the garage, I missed the oil temp sensor on top of the engine. That sensor connector was covered in oily road grime. Cleaned and reseated that connector.
The test drive was fine, drove it like a red headed step child, bounced it off of reline a couple of times without drama.
The went into storage for winter.

After studying the schemo, I am not convinced electrically that could draw more than 25 amps, or could it?
I do have a Durametric on order, so would some indication on what happen show up?

Thanks!

[Anker]

I wonder whether it is a bad voltage regulator. Put a voltmeter on the battery terminals and rev the engine up. Shouldn't get more than a hair over 14 V.

Long shot, but worth a try.

[Anser]

Thanks Anker, I pretty sure I did that last fall, but will recheck.
The Durametric should be here in a couple of days.
My plan is to read codes and see what is in there. Clear them and run the car for a bit and recheck.

I will report any findings....

[Anser]

OK, ran the Durametric and found these codes:

Engine Module
P0150= O2 sensor, pre cat. cylinder (4-6)

Airbag
Supply low
Airbag warning light

Alarm l32
21=Control Unit Failure
60=Status Not present
33=W lead DME Mobilizer
Status= Not Present

These Alarms stated info only- No Repair Needed

Xenon (car does have Litronics???)
Engine Path Left
Engine Path Right
Axle Position Sensor

What is Alarm l32?

Any other info on these would be welcome

Thanks!

[Anser]

All codes were cleared and the long drive had no dramas, nice high 60's day and good to be out!

Alarm codes as far I can find out;
21 = No engine start possible--------Makes sense, I didn't have the clutch in!
33 = No passenger compartment monitoring---Passenger monitoring sensor bad.
60 = Still don't know what status isn't present.

The big thing is the airbag and O2 errors did not come back.
I guess I did fix it

[Anser]

Well, after all spring and up until last night, was the car running without any issues.
The wife was out and about visiting clients when the problem reoccurred.
The car would just quit running. All dash lights still worked.

B8 fuse blown (DME and Immobilizer fuse) was replaced plus I had a spare fuel pump relay I installed. It fired right up.

The car ran like a top except for once a slight hesitation with a quick CEL flash.
After that no problem. We were about 20 miles from home.

I got home and hooked up the Durameteric, and no codes were present.

My next step is to go though the wiring harness for the DME and Immobilizer again and check for chaffing of wires somewhere. Yea, high 90's with matching humidity this weekend!

Any suggestions for helping track down this issue would be greatly appreciated.

Thanks!

[Gilles]

Anser,

I had a similar issue with my '07 987CS, not sure if your car has the same electrical box, but drove me nuts until accidentally found the culprit.

It was the No. 4 (positive cable from the battery to the distribution box), where it connects to the distribution box at the firewall, it's fairly easy to check.

PS: No. 11 is inside the cabin, behind the glove box, but the connector side is on the front trunk..

[Anser]

Thanks Gilles.
Checked it and the nut was tight. Still has the factory paint stripe on it.
Your idea lead me to look at the high current distribution box.
Thinking a loose connection could cause a surge.
I asked if she hit a bump when it happened, and she did.


I went to move it to have more room, and now it blows the fuse immediately.


Ideas?

[blue62]

Sounds like you need to test the wiring harness for a short with a volt meter.
If you have the Bentley service manual there is a description on how to locate a short on pg. 97-39.

[Anser]

That is the plan.
I do have a better feeling about finding the cause now that is a solid failure!

[blue62]

Originally Posted by Anser

That is the plan.
I do have a better feeling about finding the cause now that is a solid failure!

Yes a solid failure is a positive, chasing intermittent failures can be very frustrating.

[Anser]

Short from load side of fuse B8 to gnd.
Seem to be in the harness that feeds the relay box in the trunk. I was able to create or fix the short by pushing the harness close to the relays.
Pulled the relay box out and it never shorted. Was even able to fire the car up without the fuse popping.
Got as far as unwrapping and inspecting the wires, but nothing definitive yet.
It's in dare somewhere........

[Anser]

Found it! Since nothing was found in relay harness, I unwrapped the harness next to it.
Just one little section of the wire that carries the power for DME was exposed between the cloth wrap.

[blue62]

Originally Posted by Anser

Found it! Since nothing was found in relay harness, I unwrapped the harness next to it.
Just one little section of the wire that carries the power for DME was exposed between the cloth wrap.

Nice job was it shorting against the body? Or???? Mostly wondering what caused it to "chaf" in that location.

[Anser]

Not quite sure, it wouldn't beep against the painted bodywork.
All the wires around it were in good shape.
My guess is the bracket for relay carrier was the culprit.
Didn't prove it, but expose hot wire = no good.