750il Dual battery system, Ekats, SES light track down.

[Magus528]

So again...my reading form DIS




Battery temp 10°C

Battery +ve voltage, Circuit barker 2, ECAT c.m 11.8 V

Heating Current, Circuit braker 2, Ecat c.m 0 A

Fault lamp (check engine lap is on because of this fault!)




My car also came back with other TRS codes




Battery disconnect switch trs, Battery, Closed –circuit, current measurement, Charge indicator lamp, voltage control



__________________________

From Timms Repairs





Electronic Battery Disconnecting Switch

The E38 with M73 TU features a two-battery system consisting of an electrical system battery (DME supply),a starter battery (supply for the starter and elect

rically heated catalytic converter) and the disconnecting switch.



1. Start reliability The voltage of the battery for the electrical system is checked on recognition of the key contact or terminal 15.If the voltage values of the system battery U_BB are < 9 V and of the starter battery U_SB > 9 V the electronic

battery disconnecting switch for supplying all control units of the vehicle electrical system is closed for 30 seconds even if terminal 15 is deactivated during t

his period of time. The electronic disconnecting switch is opened again if no start attempt is made within this 30 second period. The switch can close again on renewed recognition of the key contact or of terminal 15.




2. Starting After the engine has been started the “engine running” signal is detected and operation of the electrically heated catalytic converter (E-cat) is triggered by the E-cat control unit. The electrical power required for this

purpose is supplied by the starter battery. The maximum operating time of the electrically heated converter is 30 seconds. At normal voltage levels, the electroni

c disconnecting switch remains open during this period of time. Once the E-cat heating period has elapsed, the disconnecting switch is closed thus connecting the system battery and starter battery. If a voltage value for the system battery U_BB of <9 V is detected the electronic disconnecting switch will remain closed until E-cat operation is detected.

In the event of a break in the “E-cat ON” line or a short to U_B the disconnecting switch will always be closed 4 seconds after detecting the engine speed signal. In the case of a short in the “E-cat ON” line to ground the electronic disconnecting switch will always be closed 60 seconds after detecting the engine speed signal.




3. Driving The electronic disconnecting switch is closed during vehicle operation to ensure the starter battery has a high

charge level at all times. The starter battery and the system battery are charged by the alternator.

If an excessively high alternator current is detected, the disconnecting switch will be opened to prevent the

alternator overloading. The alternator now only charges the system battery. The disconnecting switch is not closed again before the voltage of the system battery U_BB is higher than the voltage of the starter battery U_SB.




However, if the system voltage U_BB drops below 9 V the disconnecting switch will be closed in order to

ensure vehicle operation can continue. If U_BB < 9 V is detected three times within 1 minute during vehicle

operation, in order to maintain vehicle operation, the electronic disconnecting switch is closed permanently

and only opened again after “ignition OFF”.




4. Safety functions

The following safety functions serve the purpose of protecting the electronic disconnecting switch from

overloading: The electronic disconnecting switch opens if the preset limit current is exceeded. A check for this fa

ult is carried out at 10 second intervals. If the temperature in the electronic disconnecting switch exceeds the permissible limit the switch is opened until the temperature drops again. The module is permanently switched off under overvo

ltage conditions.




If the voltages of the system battery U_BB are < 1 V or starter battery < 1 V this is interpreted as a short-circuit. The electronic disconnecting switch remains open.





Question...is the battery disconnect switch and the battery isolator switch the same thing?

[psjr]

Yes.
If you haven't already, read up on: http://files.psjr.org/BMW_Tech/battery26-30.pdf

[740ilDuke]

Yep, the module on the side of the batteries looks identical to the EKAT module as well, but they are quite different...and neither are available anymore from BMW. Makes the 98 750 look more attractive in terms of simplicity. (No Ekat, No dual battery)

[Magus528]

Yes.
If you haven't already, read up on: http://files.psjr.org/BMW_Tech/battery26-30.pdf

Thanks psjr, I did read that document over and over again. Because my Ekat is aborting heating and causing an SES light...and I am getting indications that the Battery disconnect switch trs, Battery, Closed –circuit, current measurement, Charge indicator lamp, voltage control

Im trying to figure out the possibility that my isolator switch is bad or not. I dont want to just throw money at random parts.

[Timm]

I should think that the battery isolation switch is dead as you jump-started another vehicle from your top battery - and that would have taken more than 60 Amps:

Note:
The battery isolation switch is NOT used to boost a discharged starter battery
with the voltage of the vehicle circuit battery to start the engine.
The battery isolation switch can only withstand a maximum current flow of 60
amps.

I would guess that it has failed short-circuit so that the batteries are permanently connected to each other...

[RIboater2]

Been battling the same thing for years now. In the beginning it was rare for the ses to come on, only happened occasionally, and usually meant time for a new battery. for about a year now, replacing both batteries wouldn't solve it yet, putting either battery on a 50amp charge for an hour or so, the code would not pop for the first start up. But just drive to the corner store, come back out and start the car it would pop. That surface charge would only last for one start. Also, strangely when the outside temp was 0-10F for almost a week last winter, the code would not pop.

[Timm]

We discussed this last time - your problem is that the elements in the cats are demanding too little current - and that's because they have deteriorated with age and use. The reason that they didn't raise a code in cold weather is because the resistance of the element wire drops with temperature - and thus demands more current.

[740ilDuke]

Coding it is still the best option, long or short term. If the Ekat module was available from BMW, it'd be about $450. Coding is close to that and solves it permanently. I had access to three 750's and swapped the modules around, they all threw different codes on the same car, but solved (turned SES light off) on one. Only in the US does that system throw a light on. #dumbsystem

The isolation switch is a different bug, they no longer sell those either, but I dont know any way around it. Perhaps deleting it and changing the wiring is
an option once that fails.