TXFM

I know this has been beaten to death, but (with the help of Harold57) I was able to measure the Drain current (Ignition OFF) of the Parasitic current hogs by functions relative to the fuses. These are approx values.

2002 SC430 Total Parasitic current drain = 1.40 - 1.5 Amps (fluctuates)
Fuse 47 - Radio No.1 (Audio System) = 0.40 Amps

Fuse 43 - DC Cut (Master Fuse for Fuses 17, 18, 19 & 20) = 1.00 - 1.10 Amps
Fuse 17 - MPX-B1 (Door&SteeringLocks/Immobiliser/PowerSeat/TopRetractor) = 0.50 Amps
Fuse 18 - MPX-B3 (TiltSteer/HeadlightSwitch/WindshldWipe&Wash/TurnSignalSwitch) = 0.20 Amps
Fuse 19 - DOME (Lights/Antenna/DoorOpener/Audio) = 0.02 Amps
Fuse 20 - MPX-B2 (Guages/SkidControl/TirePressure) = 0.36 Amps

So, when Fuse 47 is removed, Total drain drops from 1.45'ish to around 1.0 Amp.
When Fuse 47 & Fuse 43 are both removed, Total Drain drops to approx 0.02 Amps - This would be good.

I don't understand why there needs to be current supplied to several of these functions (Fuses 47, 20, 18, and some functions for Fuse 17) when the ignition is off. What am I missing?
Thanks

Raven01750

Well, the door one is probably related to seat memory as well as the radio. The rest are probably related to other memory functions. Just guessing here though since I cant find my electrical manual. Its around here somewhere.

Paul

jonas's RX

Q to the experts what happens then if you remove fuse 43 permanently?

Does it mean everything in the car still work? Abs can you still start the car with
all functions other than a few stored memory is wiped out ?

It just mean there is no longer any memory
to the reset or program functions?

the next Q is does that mean if Fuse 43 is removed,
we will no longer need a trickle charger if the car has
not been driven for a while. Fuse 43 might be a good fuse
to pull if you are parked for 2-3 weeks at the airport.

Thoughts from the experts please

Wilson2000

Personally, I wouldn't bother with pulling fuses to prevent battery drain. I got five years out of my previous AGM battery which died after not driving much due to Covid. To replace it, I bought an Optima yellow top. Now I'm monitoring the battery more closely, and if it gets low, I charge it back up. Trickle charging is the answer for leaving an SC sitting for weeks on end, but there are many reasons for not leaving a vehicle sitting, beside this.

Another solution would be some sort of master cut off switch for the battery, but I wonder if keeping all the electronic control units powered down could have adverse effects. Certainly, one would lose all one's memory and learning functions, but could there be other concerns?

TXFM

I forgot to replace the #20 fuse and ran out to lunch yesterday. Car starts and runs, but you lose Skid Control, and I think the remote trunk opener didn't work either, so permanent removal of 20 or 43 probably is not a good solution.

TXFM

If you remove both 43 and 47 at the airport (or at home), the drain current is only around 0.02Amps. And you will lose all your presets.

Harold57

So there are a few issues here:

• Parasitic drain ought to be less than about 20mA. Anything above that is either an aftermarket device or a problem child. So a drain that is 50 to 70 times that amount means that there is a module that needs to be replaced.
• Fuses 17, 18 & 20 appear to have module problems in their circuits. These could be different problems or they could be a single problem that is somehow tied across circuits.
• Values this high are not normal for the car and should be tracked down

Sorry but I don't have manuals or schematics to track them down but there are others in the forum that I suspect will.
You did a great detective job of tracking down and narrowing the suspects down TXFM. I suspect that once you've found the perpetrator, your diagnosis will help others with the same issue in the forum.
If it were me, I'd start with the worst offender and work my way down.

Raven01750

TXFM, Harold is most assuredly correct. The problem with our older cars is that the electronics get older too. The biggest issue in electronics is Electrolytic Capacitors. They just naturally break down over time. On my 97 LS400, I literally had to remove the ECM and replace ALL of the capacitors on the board because they changed value enough to cause the car to run "Off" lets just say. That included the transmission. Once I replaced them all with well documented and researched components, she ran like a champ again. No issues since. So, all of these components, Radio's, Amps, ECM and ECU's are probably just showing their age. If you disconnected the radio and Amp, I bet you would see a significant reduction in bleed current. Disconnect this and that and you will find the exact electronic component in your car that is going bad most likely just due to age. Now, no one, (almost no one) would even bother taking the time to do what you have already done. They wouldn't know how to begin with. How to use a meter. How to measure current versus voltage etc. What's the easiest way to take a measurement? I SALUTE you Sir for your dedication and effort though. It was not a small task.

Paul

joemg

This is a valuable test you did... I've been thinking about trying to figure out why there is such a huge current drain for a while. Thank you for sharing this.

TXFM

Electrolytic Capacitors. Of course. Well Paul, I salute you, Sir. This [unfortunately] does make sense..
Even if I tried to remove (using the old solder-sucker) and replace all the E-lytics I would surely not have the same results as you. My pcb rework skills are not good. I guess that plugging into the trickle charger is really not that much of an effort!
Many thanks.

Seattle SCone

This desoldering station radically improved my ability to rework PC boards five years ago. Definitely one of those tools that I repeatedly hesitated buying, but upon first use, made me think "I wish I got this years ago!"


The ability to apply controlled, ample heat and simultaneous suction makes desoldering much easier and more predictable than my unheated vacuum bulbs of yesteryear.
Tips: Apply flux and fresh solder to the old joints to increase heat transfer during desoldering. Get the internal sponge damp before use. Let joint fully melt and reposition tool tip flat against PC board as solder melts. That gets you a better seal before pulling vacuum trigger. Always clean out the solder from the vacuum gun after each usage session.

Wilson2000

Hopefully, as our old-car electronics age, reconditioning services will spring up for making repairs to the ECU's.

I worked for two years at Atari in 1974 and learned to solder and do rework on circuit boards, so I thought I was capable of replacing caps on my washing machine's circuit board. The first one went well, but the last three were a be-ach! I gave up and bought an new washing machine.

TXFM

Atari in the 70's. Nolan Bushnell. Hung out at the Lion & Compass a bit when I was in the San Jose area.

Raven01750

LOL. To do quality rework on electronics requires quality tools and supplies. Solder braid is very good at pulling/wicking the old solder out. You need flux too. I prefer liquid over paste. And you need a good soldering iron with the correct size and shape tip. You should cut the old components out first. Flux both sides to remove any coating that may have been applied so the old solder will actually flow completely out of the contact. Once most of the solder is removed, heat it up again and pull the remaining piece of lead out the other side. Do one more touch with the braid and clean everything with alcohol. Flux conducts electricity and is corrosive. So a thorough cleaning with alcohol once any new components are installed is always your last step. Not for the faint of heart but really really easy once you have the technique down.

Remember. Heat is required. But too much just destroys the board.

Paul

Wilson2000

Now you tell me!

Of course I knew all these things 50 years ago when I was trained, but if you don't use it, you lose it. I have good (but not great) equipment and supplies, but my skills are super rusty, and my eyesight ain't what it used to be. Surprisingly, my hand is still as steady as a rock, which is critical when reworking a circuit board.

TXFM: Yes, right out of high school, I worked for Nolan Bushnell, and along side Jobs and Woz, but I was a lowly factory worker. Back then, all games were arcade style. The first home game, Pong, came out about the time I left. Factory work inspired me to go to college. I do think back, however, how my career/life would have turned out if I stayed at Atari and took advantage of some of the advancements offered me. Also, had I a crystal ball, I may have gotten in on the ground floor at Apple!