TakaM

Need your help.

My wife's 2007 Lexus IS250 (6spd base model) has a parasitic battery drain.
I managed to isolate it to MPX-B fuse where once I pull it, the drain is gone.
It's draining anywhere from 120 to 150 mA which about triple of what it should be.
Once I pull the fuse, the battery drain goes below 20 mA.

My mechanic also confirmed whatever connected to the MPX-B fuse is the culprit.

The challenge is this MPX-B fuse is for Multiplex Communication System which basically means it's connected to everything from ECUs, power windows, door locks, radio etc. which has 30+ devices that I would have to disconnect, one by one, to isolate the issue, plus some of them are very difficult to get to and would require for me to take the car apart.

In order to save some time and headache, have any of you experienced this issue and which device I should look for first (= which order of devices I should start checking)?

As noted above, this is250 is the base model with 6spd manual with no aftermarket parts, so it doesn't have the typically luxury electronics like navigation system and such which does reduce the population of things I have to check.

If you have any idea, it would help me a lot.
Thanks in advance.

hirsch2is

first off make sure your window switches aren't stuck. common toyota/lexus issue. if you have power folding mirrors make sure they fold all the way and aren't getting stuck. if the key is left in the vehicle or near it this can also cause a drain because the eco is constantly verifying its there(i see this a lot at my toyota dealership with pries owners). also i know you said you don't have anything aftermarket but some people over look those devices for insurance companies that plug into your old port. and I'm sure this was done but make sure you are allowing all computers to fall asleep when you are testing. this sometimes takes up to ten minutes and some people (even mechanics) don't know this.other then that close yourself in the trunk and make sure light is off and make sure all lights on the dash are turning off that should be. immobilizer should be the only one that hangs around

hirsch2is

also if you are not the original over put your head under the dash and make damn sure there is nothing that looks aftermarket under there

TakaM

Thanks for the input.
I did make sure the keys were out of range and gave probably about 30 minutes before I started testing the drain.
I did not check if the folding mirrors are stuck so I'll check those.
I did check inside car lights are all off so that wouldn't be it.
I haven't locked myself in the trunk so that will be on the list (although makes me bit nervous since I have watched the movie "Good Fellas" many times...hate to see "Tommy" with a knife when I open the trunk).

The car was purchased directly off the dealer truck with protection material still stuck so we're pretty confident that there's no anything additional that I'm not aware of.

Appreciate your input and will post if I do find anything.

Bichon

You could just put your cell phone in the trunk with the camera rolling to see whether the trunk light goes off when you close the lid. Seems a lot safer than locking yourself in.

flowrider

iTrader: (9)

^^^^Or just pull the armrest down and look thru the access hole from the back seat.

Lou

TakaM

This is what I did and confirmed there are no lights on.

Any other ideas?

ponteley

Same issue 2011 Lexus IS350 - MPX-B fuse 140 mA
Did you find solution?

2013FSport

iTrader: (2)

I know some replaced the module. There is also power distribution computer.

Do you have access to the schematics? If not, register with Toyota TIS for a few days and go through the schematics and troubleshooting guide for parasitic drain. It could be helpful.

So, roll the dice on a used ebay MPX module?

Babyblu250

I have the exact same issue coming from mpx b any solutions?

talbin

Add me to the list of people experiencing this issue. I have a 2006 IS350 with 121k miles. Isolated the draw to the MPX-B fuse. Mine was pulling 500mA and was draining my battery 25% every 24 hours.

I have zero experience working electrical but I'm watching some training videos on youtube to see if I can figure it out. Luckily I don't have to drive often so I have time to spend on this. If I find anything I'll report back.

PinnySkenis

I’ve also ran into this same issue, this fuse is pulling 700mA of draw for me! Has anyone found a solution?

2013FSport

iTrader: (2)

If I were in this situation my next step would be using techstream to test the individual modules and see if it spits anything out.

One word of caution about pulling fuses is the order one does their testing in. Under normal circumstances the vehicle is powered off and all the computers are shut down in a controlled manner. Some by a command on the CAN bus or BEAN.

Randomly pulling fuses and inserting a current meter could create false data by powering up a computer that was in communication with its buddies, lost communication and now its back online in an unknown state.

To avoid this, have your meter set to amps and inserted where the MPX fuse goes, start the vehicle, turn it off (make sure doors and hood latches indicate closed state), allow the computers to shut down and now measure your current.

Do you still get 500 to 700mA?

PinnySkenis

I’m not familiar with tech stream at all. Could you explain what it is like I’m 4 hahah. And this sounds like really good advice, thank you for the help. I should have some time tonight to test out this method and see if the draw is still there. I’ll keep you updated!

2013FSport

iTrader: (2)

Uhm, user name checks out... haha!

In short, Techstream is OEM diagnostic software that talks to Yoda/Lexus vehicles. Key ingredient is it will test each computer system in the car. I didn't know this until tonight but you can get your owners manual here too. If you subscribe to TIS, you get schematics and step by step troubleshooting guides telling you how to diagnose problems like this one. There are cheaper sites, I use www.alldatadiy.com which duplicates some of the OEM content from TIS. -->> https://techinfo.toyota.com/

Do some reading and research. Techstream is not cheap and you need the OEM Mongoose cable for full functionality.