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Discussion Starter · #1 ·
I have a 2005 accent that keeps blowing the ecu 1 fuse. It is also showing a code for "system voltage low", and the battery is wet around both posts. I read somewhere else that the alternator could be surging and blowing this fuse. Had both alternator and battery checked at autozone, battery is said to be on the way out and alternator shows its fine. Battery does not show any problems, start car just fine. Any Ideas?? Thanks in advance!
 

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More details, please.

Precisely when does the fuse blow?
Can you get the engine to run? For how long?

If it will run, measure the voltage at the battery posts.

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That fuse supplies power to the Coils of 3 relays:
Rad Fan
Cond Fan #1
Cond fan #2

Unlikely that they would be blowing the fuse.

It also supplies power to the ECU on 5 pins.

In addition, it supplies power to:
Purge Control valve
Mass Air Flow sensor

It's going to take some tricky measuring to find which item is causing the overload.

To get more info, such as diagrams, for your specific year:

Be sure to register for FREE access to the Hyundai on-line Shop Manuals. See Sticky.



Jim
 

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Discussion Starter · #3 ·
More details, please.

Precisely when does the fuse blow?
Can you get the engine to run? For how long?

If it will run, measure the voltage at the battery posts.

--------
That fuse supplies power to the Coils of 3 relays:
Rad Fan
Cond Fan #1
Cond fan #2

Unlikely that they would be blowing the fuse.

It also supplies power to the ECU on 5 pins.

In addition, it supplies power to:
Purge Control valve
Mass Air Flow sensor

It's going to take some tricky measuring to find which item is causing the overload.

To get more info, such as diagrams, for your specific year:

Be sure to register for FREE access to the Hyundai on-line Shop Manuals. See Sticky.



Jim
It will blow at any given time. It may not blow for 3 days, then it will blow 5 times in 1 day. It has not stopped car from running. I have removed the 2 relays from cond fan. and still have the problem. Autozone checked charging system, I assume that would check voltage at alt while running? I was not there during test, car actually is my step daughters. Thanks for the help
 

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Like Jim is saying, it will be tricky isolating problem.

An exact measurement of running voltage at battery would help narrow down if it is some kind of dead short.

Purge shuttle valve is part of emission system and is triggered intermittently by ECM. It is located on back of intake manifold and has a power plug going into it.

You could temporarily leave it unplugged (which will trigger mil light on dash) to see if it grounding out when triggered by ECM.

You may have damaged insulation on some wiring under the hood that eventually shorts out the fuse because of vibration/arcing.

Mass air flow is located in intake air ducting; car won't run right with it unplugged. I would give the plug and wiring on that a real close examination for damage.
 

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Discussion Starter · #6 ·
More tests

The car is now blowing the fuse as soon as the key is turned to the on position. I measured voltage at the battery while running, 14.44 volts. I used a volt meter to do some tests, I put the positive lead at battery positive, negative lead at load side of ecu-1 fuse, with key on I read 12 volts. I tried disconnecting things to see if it lost ground. I started with both o2 sensors - nothing, idle speed control - nothing, rad fans by removing relay - nothing, I already have cond. fan relay out, purge valve - nothing, blower relay - nothing. I did notice the R/W diode between the start relay and the tail lamp relay was getting warm. I looked at wiring harness to as much as I could to see if there was anything obvious, but found nothing. Anymore suggestions would be greatly appreciated.
 

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I did notice the R/W diode between the start relay and the tail lamp relay was getting warm.
I think that is the pre-excitation resistor for the alternator; it will get warm.
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Try this trick:
Take a blown fuse and attach a couple of leads from it to a small 12V bulb. Or, if easier, stuff the bulb wires into the fuse socket. Additionally, clip your voltmeter to the bulb wires; this will give you a reading of the relative load on the fuse circuit, the higher the reading, the more the load.
Anyway, this will save replacing fuses while testing.

I've included a snippet of the diagram below.
One item I don't think has been covered is the Diag Module (tank vapor system). This is located above the left rear wheel area. There is a harness plug you could pull out of it to isolate.
I added a pic of the module and my sketch of the internal circuitry.

Could be a red herring but you never know...

Jim
 

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For future lookers I had the exact same problem. The module over the rear driver side tire was to blame theres a short in the wiring that leads to the fuse. Unplugged it and problem solved. I used the light test to test all the components. Positive lead of the light to positive terminal on battery then the negative to the load side of the fuse. Obviously the fuse needs to be taken out and the load side is closest to the firewall when looking at the fuse. What happens is when you unplug the faulty system that's causing the fuse to pop the light will shut off. When that happens you found the problem.
 
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