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sprinkles08, ASE Certified Technician
Category: Car
Satisfied Customers: 23004
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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Lexus GS300: I have a 1999 GS300. Recently the battery ran

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I have a 1999 GS300. Recently the battery ran down over nigths. I then noticed that the EFI replay is continously picking (pick and release) while the engine is off and key out. I currently remove the EFI relay to prevent battery drain. I have followed threads that report similiar incidents but am not sure of the fix. Some say ignition spiral core, some say main CPU malfunction. Any suggestions or possibilities.
Hello and welcome to JustAnswer!

I see your question has been up for an extended time without a response. Do you still need help?

Customer: replied 4 years ago.

Yes,I still need help with this issue

Did this start after any work was done, accident, etc?

When the relay cycles does it appear to be in time or does it click randomly?

Customer: replied 4 years ago.

This issue started unexpectantly and after no maint or accident. The cycle time of the relay appears to be in a pattern (e.g every 6 - 7 seconds at times). If key is in ignition, the clicking (cycling of the EFI relay stops). If I remove the EFI relay the battery does not drain over time (when parked).


Do you have an aftermarket remote start?

Customer: replied 4 years ago.

No after market remote start. No after market attachments. Car is stock. Allways run fine.

This is most likely going to be the engine controller itself.

The first thing you'll need to do is unplug the engine controller and verify that the relay stops when you do.

You should find that the relay stops, and if you do then you'll want to make sure the control wire for the relay isn't shorted to another circuit from the controller. If power is coming to the relay because of a short in the wiring then it will cause the relay to come on when it shouldn't.

If the control circuit isn't shorted to another circuit then the next thing I would do is load test the engine controller's powers and grounds. A test light can be used, but it's preferred to use a headlamp or fog lamp bulb which will pull more amperage, the bulb should light as brightly as if connected directly to the battery.

If the powers and grounds are good then I would also make sure that the switched power source does go away with the key off. If there is still voltage on the switched wire when the key is in the off position then it will cause the controller to stay awake or partially awake.

If the relay circuit isn't shorted, the power and grounds check out ok then you'll need to replace the engine controller.
Customer: replied 4 years ago.

I really appreceate your time but my ECU checks out OK. I am suspecting something in the ignition system as I think that it is the ignition that is telling the ECU (MREL pin) to energize when it should not. The reason that I say this is due to the fact that when the Key is in the ignition the relay cycling stops. Obviously can't leave the key in. Grounds and power sources are connected tightly. I will do more test and checking of the ECU circuitry and respond to you tomorrow (my Thursday morning).

If it's not in the engine controller then it could be one of it's power feeds, grounds, or it's receiving voltage on it's switched source when it shouldn't.
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