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5v present on 12V when power is off


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I have the can bus 12V+ wired to the ECU power supply (PIN 59 on R32 GTR), 5V sensors go to 5V+ on the expansion port. Ground to sensor ground. the 12V line only feeds can bus (digital dash, can lambda) and the ethanol sensor.  5V for Bosch press/temp sensor and a speed sensor. all share the common ground. 

today I noticed my dash was flickering when power is off. since my dash is powered from the can bus, I tested the pins at the can bus connectors. when car is shut off, there's 4.94V at the 12V can bus line. 

what could be the possible issue ? 

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I'll verify and report back.

I think the "leak" had always been there, at least it started at some point, it's just I would've not known until I moved the wire. 

The car always had a vampire drain.

The previous shop had the 12V line wired to PIN 45. All I did was to move it to PIN 59.

Only after I moved it to PIN 59, there's some juice to make the digital dash flicker. 


The vampire drain started at some point after the car came back from the shop, all I did was changing the HKS boost controller for a Mac solenoid, it's wired to the factory boost solenoid harness. and upgraded from G4+ to G4X. 

i'll also unplug the sensors, solenoids...etc one by one to rule them out. 

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On 5/25/2022 at 12:05 AM, Adamw said:

With ecu unplugged and ign off, do you still have any voltage on pin 59 in the loom plug?

With ecu plugged back in, ign off, eccs relay unplugged, do you have any voltage on pin 59?

No voltage when ECU is unplugged. 

Eccs relay unplugged, ECU plugged in, 5v on pin 59.

but i guess i found the problem. The Mac boost control solenoid is back feeding. as soon as I unplug it, no more 5v on the 12v line. 

there's constant 12v on the boost solenoid. I used the factory harness. 

moving the 12v constant to a switched source is the only solution i guess. 

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Yes that will be your problem.  The wastegate solenoid in the factory loom is connected to the ign switch circuit/pin 45 so something has been changed there.  You will need to move this back to an ign switched source.


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