Electrical Problems

D

DavidH

Member
I have a 2003 Z4 3.0i that I purchased in March of 2003. Last August (2008) I started having problems getting the engine to turn over and eventually had to jump start it. Figuring that with 80,000 miles and 5+ years it was time for a new battery I went the the Dealer and did just that. In the year since then I have had to jump start the beast at least a dozen times and have recharged the (new) battery with a battery tender another 10-20 times. The BMW techs claimed that my after market iPod interface was drawing 100 mA and draining the battery. I only found a draw of 40 mA total myself. Recently I've had to recharge the battery more than once a week so I took the car back to the shop figuring the battery wouldn't hold a charge and they should give me a good one. They said the battery was fine.

After days of testing they found that the B+ cable (that runs from the positive side of the battery along the underside of the car and up into the engine compartment where it attaches to the positive jumper block) had melted the surrounding plastic on the jumper block and was intermittently drawing a half an Amp. The solution was to replace the B+ cable - at a cost to me of over $1200.

My questions for the Forum are: Has anyone else had this problem? and What would cause this problem?
 
I can't speak for the Z4, but as a battery strats to drain then as the volatege drops the amperage draw increases. When running Jeeps with winxhes the condition can be so severe that as a winch approaches stall and the battery start so lose charge, the draw can rise to 500+ amps. Guess what we melt calbles.

Might be a similar situation caused this.
 
Dave, I'm familiar with how the battery cable routes as I attached some wires to it along it's whole length for my rear foglight and front marker light conversion. As you may well know, the cable block you wrote of is where the starter and alternator connect to the battery cable, along with providing a place for a jumper cable. Under the side plastic cover there is a metal plate where the two wires attach with nuts (battery and the starter/alternator cable). Normally I don't see how that area could get hot unless it was arcing to ground at that location, perhaps it is a designed weak spot making it the first place to fail if any part of the battery/alternator/starter cable arc to ground.

cj10jeeper: Interesting about how a weak battery condition can cause high amp loads & melting cable sheaths, never heard of that one :thumbsup:
 
MarkC said:
Dave, I'm familiar with how the battery cable routes as I attached some wires to it along it's whole length for my rear foglight and front marker light conversion. As you may well know, the cable block you wrote of is where the starter and alternator connect to the battery cable, along with providing a place for a jumper cable. Under the side plastic cover there is a metal plate where the two wires attach with nuts (battery and the starter/alternator cable). Normally I don't see how that area could get hot unless it was arcing to ground at that location, perhaps it is a designed weak spot making it the first place to fail if any part of the battery/alternator/starter cable arc to ground.

cj10jeeper: Interesting about how a weak battery condition can cause high amp loads & melting cable sheaths, never heard of that one :thumbsup:
Click to expand...

Probably not something that would ever be experienced on a normal car. When we winch real hard and I mean lifting the Jeep near vertical for perhaps 50 metres the alternator cannot keep pace with the current draw. As the battery discharges it's voltage will drop. The winch demands the same or more current in an effort to keep working and pushes the amps through the roof. I oft see 500amp peak draw on a 6hp if the voltage dips to 10 to 12 Vs normal 14, winch so have cables thicker than my thumb. (It's for this sort of reason that Zeds have what looks a massively overthick starter cable from rear battery to starter to prevent voltage drop in the cable.)

I last witnessed this less than 2 months ago when one Jeep winched another out of a gulley. As the guy had failed to fit a kill switch, there was no way to break the circuit when the winch contacts momentarily fused 'on'. It winched to the point of the 2 Jeeps being pressed bumper to bumper together, winch stalled and battery started to drain. The driver raced to disconnect the battery as the loom started to melt then drip it's coating off and our acrid smoke out. Comical, but bloody dangerous :evil:


I believe that partial arching to earth of a live cable can also have some pretty dramatic effects over time.
 
cj10jeeper said:
I can't speak for the Z4, but as a battery strats to drain then as the volatege drops the amperage draw increases. When running Jeeps with winxhes the condition can be so severe that as a winch approaches stall and the battery start so lose charge, the draw can rise to 500+ amps. Guess what we melt calbles.

Might be a similar situation caused this.
Click to expand...


What Jeep have you got - I run a 2009 Wragler Sahara 3.8 v6.
 
1985 CJ10a (small block Chevy)
1998 TJ for competition use

Both fairly tricked up bits of kit :thumbsup:

Not had a lot to do with the latest incarnation of the Jeep but I hear it's a lot more comfortable

DSC01354.jpg


cj10jeepfest.jpg
 
If you really think that the Battery cable is your problem, then you MUST replace it. It is tied directly into the SRS monitoring system so that (the SRS) can monitor the cable for faults.

B-Cable.jpg


B+ Monitored Battery Cable
1. Outer insulation
2. Monitoring Shield
3. Insulation of aluminum cable
4. Aluminum cable 35mm2

The E85 B+ Battery Cable is routed from trunk area along the underside of the car into the engine compartment. If the cable is damaged in an accident or while driver over an obstacle,
the BST is activated, protecting the vehicle from further electrical problems.
The battery cable monitoring occurs via the low impedance shield of the battery cable, the monitoring shield. The monitoring point in the trunk at the BST is connected to the SBSR
and the other monitoring connection in the engine compartment is connected to the SBSL. B-Pillar Satellites (SBSL and SBSR)

Battery Cable Monitoring
The battery cable is diagnosed by a special circuit between the SBSL and SBSR satellites.
The battery cable diagnosis takes place across the low impedance shield of the battery cable (monitoring shield). The monitoring shield monitors the state of the battery cable
as follows:
There are connections to the left B-pillar satellite and the right B-pillar satellite at both ends of the shield. This means that there is usually the same voltage at the
analog/digital converters in the satellites. If the voltages differ, there is a fault.
The monitoring shield consists of a low-impedance metal mesh. A connection cable exits from each end of the monitoring shield (at the safety battery terminal in the luggage compartment
and at the battery earth point in the engine compartment).
The connection at the safety battery terminal in the luggage compartment is connected to the right B-pillar satellite. The second connection cable in the engine compartment is connected
to the left B-pillar satellite.
The satellites contain analog/digital converters that are connected to the microprocessor of the satellite. The connection cables of the battery cable diagnosis are connected to the A/D
converters.
The right B-pillar satellite contains a pull-up resistor.
The left B-pillar satellite contains a pull-down resistor of the same size.
The voltage supply of the satellite (approx. 10 V) is applied at the pull-up resistor. Ground is applied at the pull-down resistor.
The very low-impedance cable and the resistors of the same size mean that around half the voltage (approx. 5 V) is applied at the A/D converters.
Every 250 μs, the values are measured, triggered by the synchronization pulse. If the battery cable is OK, the values are transferred every 20 ms to the SIM. If a significant deviation
of the values occurs, the new values are transferred immediately.
In the following cases, the battery cable is cut off by the safety battery terminal from the battery and the alternator is switched off:

• Short circuit to ground (body)
• Short to battery positive

If the outer insulation is damaged (e.g. due to friction/scuffing), but the monitoring shield has no connection to ground, the following case could occur:
Moisture (rain) would mean that the voltage would gradually fall. A short circuit to ground would be detected, but the safety battery terminal would not be triggered.
The entry "Implausible measured value" is set in the fault code memory. This would be indicated to the driver by the airbag warning lamp.

Service Notes
The following must be observed by Service:
• Battery cable diagnosis
• Safety battery terminal
• Airbag warning lamp

Battery cable diagnosis
If the shielding of the battery cable is damaged, the battery cable must be replaced completely.
It is not permitted to repair the shielding.

Safety battery terminal
If the safety battery terminal is activated, the battery cable must be replaced completely.
Repair is not intended.
 
I just got back from a 5000 mile trip to New England and back. I now have no doubt that the cable was the source of my electrical problems for the last year. The engine now turns over energetically each time I start it. It doesn't sound like anyone else has had this problem. The arcing to ground sounds like a reasonable source for the melting- perhaps it wasn't bolted down well. Now that I'm back I'll post a picture of the damage.
 
I have a 2003 Z4 3.0. I keep getting a batrtery light. I used a DIS program for diagnostics and get a message "Battery cable shield open". I also get a message that there is only 12.4 volts but a voltmeter measures 13.2 volts. I am guessing that the B+ cable has a problem. Voltage measurement is a calculation from B+ to the shield as I understand what I have read.

I also find that the Book CHILTON BMW 3Series /Z4 is a waste of money. It is a canned text that would fit any car. with very little car specific information. This forum has much better information
 
I have a 2003 Z4 and have been having a charging problem for months. I read many post that the battery had to be registered. This is not so on a 2003, but yes since 2006. I was getting an error from a DIS diagnostic program that the "shield was open". I finally checked the resistance on the shield from the battery to the post under the hood. It was good "zero". I cleaned the connectors on the shield (a small 2 pin connector with only 1 pin inside). Now all is good and the battery light is off. What a pain this has been.
 
I finally fixed the problem with charging. I had bought a rebuilt Duralast alternator from Autozone and the voltage regulator was bad. I found that they do not check the regulator. They just replace all wear parts on the alternator and the brushes in the regulator. I replaced the regulator with a new one from NAPA and everything works now. In retrospect I would have been better off to replace the alternator with a new Bosch alternator from NAPA. I would have saves $50.00 and many hours of troubleshooting.
 
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