1998 LS400 parasitic drain from obd fuse & mystery extra fuse not on diagram

[Supafly]

I've finally got round to replacing the fuse in my multi meter and started to investigate the drain I have had on my LS400.

0.17a resting draw which I've narrowed down to the OBD fuse, which when I pull out drops to 0.08.

I then put the OBD fuse back in and tested all the inside fuses and none of them made any difference.

It was at this point that I noticed another white fuse next to the OBD fuse, there is no mention of this on the diagram under the cover.  With the OBD fuse removed and this 'mystery' fuse removed the drain dropped to 0.04a (which then rises to nearly 3a and then settles to 0.08 after a few minutes).

 

I'm at a loss now how to proceed, does anyone know what the OBD fuse powers?  Also does anyone know what this 'mystery' fuse is? (see photo attached)

There is an old thread where someone has an almost identical issue but the resolution/follow up was never posted.

 

I have LPG fitted and there is a nokia car kit installed in the centre arm rest.. I will look to eliminate these as potential sources of the drain tomorrow.

 

Thank you for your time and help

[Mihanicos]

If you cannot identify it, remove it and find out what does not work.

Autodata circuit diagrams are very accurate and very thorough.

Chris

[Razor61]

Don't know if this diagram below is correct for your car but it it may help. According to this diagram it's a 'short pin' and the wiring diagram from the manual, also shown below, says 'Short Pin' which seems to feed the Dome, OBD, ECU-B and MPX-B fuses maybe?

[Supafly]

7 hours ago, Mihanicos said:

If you cannot identify it, remove it and find out what does not work.

Autodata circuit diagrams are very accurate and very thorough.

Chris

Hi Chris,

Thank you for the tip.  I actually did just that earlier this morning and pulled the OBD fuse and took the car for a drive.  I couldn't see that anything wasn't working.  I used to have access to autodata many years ago but unfortunately don't have access any more.

 

I also concluded that the lpg system is independent of this OBD circuit as it was functioning normally with the fuse out.

 

[Supafly]

49 minutes ago, Razor61 said:

Don't know if this diagram below is correct for your car but it it may help. According to this diagram it's a 'short pin' and the wiring diagram from the manual, also shown below, says 'Short Pin' which seems to feed the Dome, OBD, ECU-B and MPX-B fuses maybe?

Hi Paul,

I really appreciate you taking the time to post up this response and the diagrams.

They definitely do help! 🙂

The first image is a perfect representation of my fusebox and clears the 'mystery' up.  I too did manage to find the second diagram last night while surfing for answers, but I couldn't get any further down to see what followed after the OBD fuse.

[Supafly]

Update

I've put in a bosch Battery from another car and have been using the car for short journeys with the OBD fuse removed and everything seems to be working fine.

Although 0.08a is on the high side I think I'll be ok with this level of drain and the usage I have with the care.

When I get time to check the other fuses I'll update this thread again if I resolve the issue further.

[ambermarine]

My Mark 4 was fitted with a tracker by Lexus as they owned it for its first year as a demonstrator and it is portrayed in a Lexus format on the drivers window next to the warnings of radio disfunction if removed

The tracker is still in there and still works so I have a drain which will flatten the Battery in a month .The car is constantly connected to an intelligent charger when not in use which is never longer than a week but even a partly discharged Battery can result in gremlins appearing in the electronic systems of the car.

It may be worth checking if your car of the same year had a tracker fitted as it seemed to be a trend was developing around that time.

[Supafly]

Thank you for the tip.  I've just been outside to check the drivers window and I have two 'stickers/labels' and one etching.

I've got the WARNING - RADIO WILL NOT WORK IF REMOVED 

Below it there is - LEXUS AUTO ALARM

Then below that a code etched into the glass with a telephone number below it.

 

Is the tracker label different to the AUTO ALARM label?

[ambermarine]

This is the sticker you don't have one but the tracker could still be installed by another company.

[Supafly]

Thank you for clarifying, hopefully this will also help others in the future.

From what I can gather at the moment, leaving the OBD fuse out means that there is no power for the plug which is easily fixed if ever I or anyone else needs to plug in a reader.  Driving the car recently I'm not aware of anything not working, so if there is a tracker or the car phone is tapped into this permanent live then it doesn't affect my usage of the car.

When I get some more time I'll try and investigate the relatively high drain from the Dome, OBD, ECU-B and MPX-B fuses.  This can become quite technical and I do not have an oscilloscope, so if I can't find anything obvious I may just call it a day.  I use the car at least once or more a week and with the new 130amp alternator and Battery, I think this level of drain shouldn't (hope I don't have to eat my words!) be an issue.

[Tulpen]

I've mentioned this before.

My Battery went duff and my local Lexus dealer fitted a new one. Six months later, after sitting idle for about 10 days, the Battery went flat again. The dealer replaced the Battery, free, but a few months later the same thing happened after the car had an idle period. Once again, the dealer gave me a free replacement but, this time, they took the car in for an in-depth check of the electrics.

When new, the car had been the garage demonstrator and the insurance company had insisted that a 'Track and Trace' theft system was fitted. The system came with 2 years free subscription. After the 2 years, the garage didn't bother to continue the payment, but the system was still there and using Battery power. 

If the car sat idle for more than a week, the tracker drained the Battery. The dealer disconnected the tracker power but couldn't remove the hardware because it was fitted in a 'very difficult to remove' position (makes sense doesn't it?)

I've had no problems since.

[Herbie]

21 hours ago, Supafly said:

This can become quite technical and I do not have an oscilloscope,

I bought one of these oscilloscopes and they're surprisingly good and accurate. I bought mine as a kit and did all the soldering myself but this one appears to be ready-built and all you have to do is assemble the case.

Being small, portable and working from a 9V supply, this would seem to be ideal for work on the car and at just over £20, what's not to like?

[Supafly]

On 4/27/2022 at 10:48 AM, Tulpen said:

I've mentioned this before.

My battery went duff and my local Lexus dealer fitted a new one. Six months later, after sitting idle for about 10 days, the battery went flat again. The dealer replaced the battery, free, but a few months later the same thing happened after the car had an idle period. Once again, the dealer gave me a free replacement but, this time, they took the car in for an in-depth check of the electrics.

When new, the car had been the garage demonstrator and the insurance company had insisted that a 'Track and Trace' theft system was fitted. The system came with 2 years free subscription. After the 2 years, the garage didn't bother to continue the payment, but the system was still there and using battery power. 

If the car sat idle for more than a week, the tracker drained the battery. The dealer disconnected the tracker power but couldn't remove the hardware because it was fitted in a 'very difficult to remove' position (makes sense doesn't it?)

I've had no problems since.

Thanks for the insight Brian,

I don't think I have a factory tracker but that doesn't mean that someone hasn't fitted one.  The benefit/problem with them is that they are fitted in such a way to make detection very difficult.  I think I'll have my work cut out trying to find one if it is fitted.

Luckily for me the main drain is coming from the OBD fuse which means something is draining from a permanent live.  As it seems like it's only supposed to power the diagnostics plug, leaving the fuse out has given me an easily reversible fix.

[Supafly]

22 hours ago, Herbie said:

I bought one of these oscilloscopes and they're surprisingly good and accurate. I bought mine as a kit and did all the soldering myself but this one appears to be ready-built and all you have to do is assemble the case.

Being small, portable and working from a 9V supply, this would seem to be ideal for work on the car and at just over £20, what's not to like?

That's brilliant!!

 

Thank you ever so much for the link.  The last time I checked they were kits and around £90.  I'm confident assembling electronics but the price at the time was still too much for such an occasional tool.

This however is a no brainer! Off to order one now 🙂