Voltage on accessory line in ECU?

Frozen Fractals · 10-22-2016, 05:22 AM

My angel eyes stopped running the other day (I am using Daeos Vista harness). I decided to check the voltages to see if a fuse blew or the relay went out. I did some probing and read only 4.88V on the line to the angel eyes. I know it's supposed to be 12V. I popped open the ECU cover to where I tapped the accessory line (red wire with white stripes)...I measured it directly off of the tap from that wire and it read 4.88V (thus eliminating anything down the line...i.e. the harness). Does anyone know what can cause this low voltage reading on the red wire with white stripes in the ECU? Bad fuse? Or worse?

Thanks!

Donutz · 10-22-2016, 09:54 AM

Chuck that harness in the trash and get your car coded. I had that harness on my car (was installed by the previous owner), and I had all kinds of problems from one side going out, to one side being dimmer than the other, to dme relay codes, and a couple of other issues.

I realize that this info doesn't answer any of your questions.

Fundguy1 · 10-22-2016, 10:07 AM

Possible causes, bad battery, bad harness, bad alternator, bad voltage regulator, bad engine ground.

Frozen Fractals · 10-22-2016, 11:24 PM

Figured it out!

I found the wiring diagram and traced that particular wire to a 10A fuse in the ECU box. That particular fuse also protected the DME cooling fan amongst other things (DMTL pump, flaps, etc.). I drove the car (with the ECU box open and the cabin air filter off!) to my local parts store and grabbed some new fuses. Popped the new one in and also replaced the Daeos harness's fuse to a 10A one so it doesn't blow the other fuse when something shorts (stupid how the put a 30A one in there when it's attached to a 10A fused circuit!!!)...speaking of shorts...I'm betting that I might have some exposed wires in the headlight wiring that caused a short to blow the fuse...need to hunt for that now!

10-22-2016, 05:22 AM	#1
Frozen Fractals First Lieutenant 163 Rep 321 Posts Drives: 2018 540i xDrive Join Date: Jun 2015 Location: US / China iTrader: (2)	Voltage on accessory line in ECU? My angel eyes stopped running the other day (I am using Daeos Vista harness). I decided to check the voltages to see if a fuse blew or the relay went out. I did some probing and read only 4.88V on the line to the angel eyes. I know it's supposed to be 12V. I popped open the ECU cover to where I tapped the accessory line (red wire with white stripes)...I measured it directly off of the tap from that wire and it read 4.88V (thus eliminating anything down the line...i.e. the harness). Does anyone know what can cause this low voltage reading on the red wire with white stripes in the ECU? Bad fuse? Or worse? Thanks!
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10-22-2016, 09:54 AM	#2
Donutz Lieutenant 140 Rep 476 Posts Drives: 335i Join Date: Sep 2015 Location: Toronto, eh iTrader: (2)	Chuck that harness in the trash and get your car coded. I had that harness on my car (was installed by the previous owner), and I had all kinds of problems from one side going out, to one side being dimmer than the other, to dme relay codes, and a couple of other issues. I realize that this info doesn't answer any of your questions.
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10-22-2016, 10:07 AM	#3
Fundguy1 Major General 2032 Rep 8,339 Posts Drives: 335 e93 Join Date: Aug 2014 Location: Orlando, fl iTrader: (0)	Possible causes, bad battery, bad harness, bad alternator, bad voltage regulator, bad engine ground.
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10-22-2016, 11:24 PM	#4
Frozen Fractals First Lieutenant 163 Rep 321 Posts Drives: 2018 540i xDrive Join Date: Jun 2015 Location: US / China iTrader: (2)	Figured it out! I found the wiring diagram and traced that particular wire to a 10A fuse in the ECU box. That particular fuse also protected the DME cooling fan amongst other things (DMTL pump, flaps, etc.). I drove the car (with the ECU box open and the cabin air filter off!) to my local parts store and grabbed some new fuses. Popped the new one in and also replaced the Daeos harness's fuse to a 10A one so it doesn't blow the other fuse when something shorts (stupid how the put a 30A one in there when it's attached to a 10A fused circuit!!!)...speaking of shorts...I'm betting that I might have some exposed wires in the headlight wiring that caused a short to blow the fuse...need to hunt for that now!
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