1994 Lexus SC 400 1.68 amp drain from EFI fuse

  • 1994 LEXUS SC 400
  • V8
  • 2WD
  • 147,000 MILES
I've got a 1994 Lexus SC400 and have had the battery dying on me (takes anywhere from 8 hours to 3 days to die)for over a year. Everything functions as it should but the battery dies if the car sits for more than a day.

Long story short, after over a year of trying to temporarily solve this problem with all kinds of haphazard chargers, brains, switches, and batteries, I've finally made "actual" progress towards a solution.

I've tested the parasitic draw at least 100 times (no joke; probably closer to 500) and I've never gotten a reading over.075ma. It may seem a little high but a good battery should still last a couple of weeks with such a draw; my battery would only last 8 hours to 3 days max. This is what always stumped me. Then I stumbled upon an article which said that while testing for a parasitic drain/draw a battery disconnect switch may be needed to insure that unplugging the battery does not effect the test.

After following the instructions from the link and without disconnecting the battery, I got a reading of 1.68 AMPS! When the EFI fuse was removed the drain dropped to an acceptable.053 ma. When the EFI fuse was replaced, the drain stayed at.053ma (that's the tricky part that has been stumping me). The 1.6 amp draw was also erased when the main efi relay was removed. I switch the efi relay with another one, but got the same results so the relay is NOT the problem (I think).

I've got a 1.68 amp drain that drops to.052 ma when I remove the EFI fuse or EFI relay. But if I put the fuse (or relay) back in it's socket the drain remains at.052 ma. The drain goes back to 1.6 amps once I turn the key into the ACC or ON position (the position when you turn the key all the way w/o trying to crank the engine).

Any ideas of what would cause an approximate 1.6 amp draw in this circuit? How to check/fix this?

Wednesday, January 20th, 2010 AT 7:04 PM

1 Reply

  • 11,533 POSTS
You need to eliminate everything on that circuit one at a time until the draw goes away. You can sign up for our online manual with the wiring diagrams for "Engine performance" and it has all of the circuits that are powered up by the main EFI ralay. That relay goes to ignition, injection, PCM, alot of places. The wiring diagrams are printable, so itis a one time buy, may be a good investment for the vehicle if you plan on keeping it. Does the draw change when you remove any other fuses? Like ign, inj, anything else that may help narrow it down?
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Tuesday, January 26th, 2010 AT 7:56 AM

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