MUX/T TOW fuse draining battery

[RCJP]

Hi to all
I have a 98 grand Cherokee 4x4 4.0L 6cyl.

My battery is being drained tothe point were it will not stay charged even if a disconect de terminals.
this is what i´ve done

I disconected the PCM, took out all the fuse that are in passenger side, disconected the module that is under the hand bracke, the starter also disconected,. and with a current tester I still found some current flow. SO i went to the fuse box that is next to the battery (while all of the above were disconected and no fuses)and when i took out the MUX/T TOW fuse current went to zero.

so my question is what does this fuse power?
becasue this is the second battery in 3 weeks i dont want to buy another untill i fix this
please help

thank you

 

[SteelHeadz]

Did you mean MAXI Tow fuse?. What fuse number is it?

 

[RCJP]

Did you mean MAXI Tow fuse?. What fuse number is it?

hi Steel Headz no iu do mean MUX/T TOW that is what it says on the fuse box cover.

 

[SteelHeadz]

hi Steel Headz no iu do mean MUX/T TOW that is what it says on the fuse box cover.

Is there a Fuse #? . I've been searching and reading all the circuits on both factory and aftermarket tow wiring diagrams and cannot find that. I even tried looking into the export model, still none.

 

[RCJP]

Is there a Fuse #? . I've been searching and reading all the circuits on both factory and aftermarket tow wiring diagrams and cannot find that. I even tried looking into the export model, still none.

i will have to check i'm at work now only other info i remember now is that it is a 50Amp fuse
and it is in the fuse BOX that is under the hood just behind the battery

 

[RCJP]

hi I could not find any fuse number on the power distribution box, sorry i dont know what else i could look at to give more info on what FUSE i'm talking about:???:

 

[SteelHeadz]

Even a Pic with an arrow pointing to the fuse would do..

 

[RCJP]

HI

sorry this took so long i attached the pictures hope this helps

 

[SteelHeadz]

Okie dokie, I feel really stupid after you posted the pic.. The whole time, i kept reading it as Muxit tow fuse. after you posted that pic, i can understand now that it's a Mux / T. Tow fuse. lol. Anyway's , here it is. The schematic Diagram looks pretty simple from the PDC to the Junction block. This is where it gets a little complicated(From the junction block). The circuits Splits(junctions) out to multiple modules such as the DDM(Driver door module), PDM(passenger door module), BCM(Body control module), Auto day and night mirror and stop lamp switch. Let me know where you want to start on your venture trying to figure this out. I have dug up a lot of Diagrams but too much to post all at the same time.. Just let me know.

 

[RCJP]

Hi lets start with the Body control module,

another clue i found last night, after installing all the fuses in the kick panel back, I also the MUX/T TOW fuse I saw that the current cunsuption got higher So I took out 1-by-1 all th fuses in the kick panel and found that Fuse #17 (RAD ILLUM) is creating even more consuption.
So in order to eliminate consuption I have to take out the MUX/T TOW fuse in PDC and the RAD ILLUM fuse in the kick panel.

thank you

 

[SteelHeadz]

Be aware that the Body control module will stay awake at a pre-dertermined time before it goes on stand by. If the veh is equipped with a Central Timer Module thats separate from the BCM, then the CTM needs to time out before the BCM can start its countdown for its sleep/ Stand by mode. Give the modules around 45 to 60 seconds to time out before you measure voltage draw..

 

[RCJP]

OK so were would you recomend I start.

 

[SteelHeadz]

Out of curiosity , on your first post when you said the battery would not stay charged even when you disconnect the terminals, did you mean battery terminals?.. If so, there is no way that the vehicle can drain the battery if it's not even hooked up. Moving on to the diagnostics, if we still need to. I would first start looking at all the interior lamps. Make sure they all turn off. Check the glove box lamp, vanity lamps,ash tray lamps for proper shut down.
The 1996-1998 ZJ body vehicles(Grand cherokee and Laredo) uses a body controller to control many of the body systems that previously used stand alone modules. There is only one"Level" of BCM available as opposed to othe vehicle lines that uses a base or premium controller. To send and receive information, the modules utilize the CCD bus currently used on other Chrysler vehicles. The bus is supplied bias or power from three different modules. The BCM and both the drivers door module(DDM) and the passenger door module(PDM) can provide bus bias. Normally the door modules only provide bias until their message has been sent, if the BCM is in a sleep mode. After the BCM wakes up, it takes over the biasing of the bus.
Termination is provided from two modules, the PCM and the BCM. as in other systems, termination is used to control the voltage level of the bus. Termination resistors used in the PCM and BCM typically measure 120 ohms of resistance each. most bus systems use two points of termination, and they are wired in parallel, then the total resistance of the bus circuit would equal approximately 60 ohms. this measurement could be made at the DLC(Diagnostic link connector) after the bus becomes inactive.
The body control module provides or supports the following features:

Intermittent wipe control
Door ,hood, liftgate,rear glass ajar status,reading and transmitting of external temperature
A/C select switch status
Chime
Courtesy lamps(including Halo) with time-out feature
auto headlamp control
Headlamp delay
Illuminated entry
Instrument panel dimming
Vehicle theft security system with panic mode
Door lock inhibit(Key in ignition or headlamp/ Park lamps on)
electronic odometer support
Brake pressure / Park brake switch diagnostics
High beam indicator
seatbelt minder
speed sensitive intermittent wipe control
Fog lamp control
Remote radio controls and support
Mechanical instrument cluster support
BCM diagnostic support
Vehicle information Center
Liftgate courtesy lamp disable
Rear window defogger control

The BCM provides the PCM with information on the A/C switch status and the "OK to start" or VTSS status.

 

[RCJP]

Hi, well what i mean is that what ever is dscharging the battery got it so damaged that now it wont retain the charge and so i dont want to buy another one before I fix the problem, the diagnostics that i´m doing are posible because of the small charge that is still on the battery.

So will keep looking for what is wrong.

thank you.

 

[SteelHeadz]

Sorry, I got tired typing last night. Here's a couple of diagrams to get started.

 

[RCJP]

Hi thank you for the schematic, so yestaerday I took out fuses # 7, 8, 9 from the junction Blcok they are all connected the MUC/T TOW fuse.
consuption continued so I went to circuit bracker 2(30A) the one that powers the passenger/driver door modules. and finally consuption stoped.
so now the thing was to take out the modules i took the passenger side first en the consuption stoped! yei!. then I went to the driver side and also took out that module so that i could out the passenger module on the driver module an comsuption started again.

I finnaly found my multi-meter and measure the exact current so with the circuit braker out the current measures 14mA with the driver module on the current goes up to 16mA (2mA difference), when the passenger side is connected it goes up to 24mA (8mA difference), I want to go and get a passenger door module but i need to hear youre advise first because while the passenger door module consumes 4X what the driver side does it seems like very little current to me, but i'm not that familiar with current values on cars.

thanks again I think we are close

 

[SteelHeadz]

Before you condem the DDM or the PDM, did you let the BCM go on the "Sleep mode"?, cause if you didn't , the test you just did will be inaccurate. . The difference in voltage flow between the PDM and the DDM will vary due to the added support of the RKE. Im not sure if it's the DDM or the PDM that is requested by the BCM to program the RKE and Skim if equipped. Right now i'm leaning towards the BCM for the battery draw issue.

 

[RCJP]

Hi, even if all the fuses in the junction block are currently out will the BCM still be operating?..

anyway I just got my hands on a 96 ZJ service manual and i'm going trough the scematics i will go trough the BCM wiring next.

thanks

 

[RCJP]

Hi
i put fuse #7 back on the Junciton block, this powers the BCM,
I measusred the current and it was 200mA !... so I shut all doors, locked the car and waited about 30min for the sleep mode measured again and still the 200mA were present so i disconeected the the power connector for the BCM and current went to close to zero.

toughts?

thank you

 

[SteelHeadz]

If all the other modules has timed out and the BCM is still awake after 30 mins(Too long) , then i would assume that the BCM has an internal fault.