ECU either junk or not going into sleep mode.

[zyklon]

The car: 1989 325i

The problem: This weekend, I dragged out the multimeter and dug into my car, trying to figure out why there was a constant 5 amp draw from my battery, even when the car's off.

After MUCH damn digging, it turns out to be the ECU. It's pulling a constant 5A. I can't decide whether it's the ECU gone bad or some accessory is keeping it awake constantly. It should be mentioned the car runs 110% fine even with this ECU issue, so I know the ECU isn't totally junk, just possibly junk-ISH.

I've never had to diagnose a car this deeply into A-level territory as I'm a B-level tech at my shop, so I'm a bit lost. Alldata, Identifix, etc have no leads for me either, so here I am at R3V because I love you guys.

The question: Should I spend the money on another ECU, dig deeper to find what's possibly causing the ECU to stay awake, or go with my big stupid idea of installing a toggle switch on the ECU hot to force it to shut off?

[ST1G]

How do you know the ECU is pulling the 5A? Did you test the pins? If so, which pin was pulling the 5A? Does this pin pull 5A when the ecu is unplugged? If not, how do you know it's the ECU?

[modernist]

Relays get sticky with age

[AndrewBird]

5 AMP? Are you sure it's not 5mA?

I don't think the ECU pulls that much amperage even with the engine running, so there is either a short, or you aren't reading your multimeter correctly.