2005.5 Jetta TDI F10 fuse blowing

I had a boost problem. At first there was second or two delay in boost becoming a longer delay till boost totally lost. Codes thrown were P0243, 245 & 2425.

I replaced the N75 which appeared to be bad but that changed nothing. I checked the wiring and the N75 was only getting 0.75 volts on the positive. I checked more and the F10 fuse was blown. So, I replaced and the boost was back... no problem for about 24 hours then the boost suddenly left again. I replaced the F10 fuse again and boost lasted about five minutes. Codes had returned each time the fuse blew. I looked up the circuits for the F10 fuse it appears to be related to the N75, N18, and sensors like the G130, 131, 70 and 42. I pulled the plug on the N18, put in a new fuse and it blew so I figure it's not the N18, EGR Cooling Valve Control Circuit.

I had to order new fuses. I'm thinking to pull the plug on the N75 and see if the fuse blows. If it blows, Next steps may be to pull some of the sensors like the G130, 131, 70, and 42. I don't know whether the F10 fuse controls the actuator that moves the vanes on the turbo charger but maybe I'll try disconnecting that plug and see if a fuse still blows.

I'm slow on electrical circuits and don't know enough to run multimeter testing on the plugs or the actuators so I've been trying one fuse at a time. Of course, I could just plug in a 30 amp fuse and check for smoke from the hood when driving (NOT). ;-D
Any suggestions are much appreciated.

I would also check the wiring harness. If you have availability of a circuit tracer which will show a short, that would be the easiest, in my opinion.

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I purchased a circuit tracer and either it was a dud, I don't know what I'm doing or there's something strange going on. I turned the tone generator on, placed the probe on the ground of the N75 plug and the whole body of the car responds to the tone sensor. When I ran a continuity test of the same ground of the N75 plug, there was no continuity. I visually traced the wire going to the N75 and it goes behind the battery into a bundle of wires about 1" in diameter and then into the firewall. It looks like it runs to the interior fuse box but I haven't gotten under the dash to see where it goes. The wiring going to the N75 plug looks OK. From what I could find online, if there's a problem with a wiring short, it usually occurs close to the plug and not in the wrapped bundle of wiring in the harness. However, I can't recall if I checked the continuity before or after I found the blown fuse so I need to run through the diagnostics again with a good fuse in place.

OK, I checked continuity and there was no continuity on the ground side of the N75 plug. I also disconnected the N75 plug, put in a fresh 10 amp F10 fuse. When I started the engine, it blew without the N75 being plugged in. I tested the voltage on the plug with a fuse inserted and there was 11 volts at the plug.
I did the same with the N18 and the F10 fuse blew when I started the engine.
Because the F10 fuse also appears to be connected to the G70, 42, 130 and 131, I looked up those sensors. the G70 is the MAF sensor and it throws a different code when problematic. The same with the G42 intake air temp sensor (IAT). It throws a P0275 when problematic as do the G130 and 131.
So, it looks like I'm stuck with a bad N75 or N18 from thrown codes of P0243, P0245, and P2426. Of concern is that reference is made of possible problems with the ECU.

Would a short occur and blow the F10 fuse even if the N75 and N18 were disconnected?

You have a problem in the wiring.

A short to ground on a power leg.

A neat trick for finding shorts:

make yourself some wires with male terminals on one end, and some large females on the other, a few feet long.

Plug each wire's male lead into one side of the fuse terminal that keeps blowing, then run each wire's female lead to a sealed beam headlight bulb, like a 6054. You are essentially replacing the fuse with a large bulb. If it is shorted, the bulb will just light up. But it can carry enough current to complete the circuit if it is not shorted, and will NOT light up.

Doing it this way, while the bulb is plugged in, you can wiggle around on the wiring to the consumer (in this case, the N75) all the way back to the fuse box, and watch to see if the light flickers, goes out, gets bright, etc. Narrow down WHERE the short actually is.

On the BRM, the N75 is not in the engine harness, but that doesn't mean that fuse doesn't go to something that is. You'd need to examine the EDC wiring schematic to be sure.

You may also what to pull up the underhood fuse box and check for corrosion underneath, where it connects.

Good suggestions for problem solving. I tried to find the problem for several hours today. I tested the voltage between the 10 amp fuse legs and it was 12.8 without the motor running and 14.4 volts running. I tried to check the amps between the fuse terminal legs and blew the 10 amp fuse in my meter. I had the meter set to show up to 99.99 amps. When I inserted a 10 amp fuse in the terminal, it popped loudly. So, it is a short. I followed Mosambiquer's advice and ran a cheap circuit tracer on each of the fuse terminal legs after disconnecting the battery. The results were strange. The tone detector had the strongest signal anywhere on the motor. So the short must be where a wire is pinched against the motor and something attached to the motor. Around a month before the problem started, I had the egr cooler, the clutch, and the X-member and dogbone replaced. After the work, there was a vibration when the rpms ran up that sounded like a heat shield was a bit loose. I crawled around under the car and wriggled things but did not find the source of the vibration. Then the boost became intermittent with more and more delay before the turbo spun up and finally there was no more boost. I'm guessing that the insulation on the wire was wearing through and when it finally wore through, there was a short and no more boost. I thought it was the N75 or N18 after research. I purchased another N75 and installed it. Still no boost. I went back to the mechanic and he ran diagnostics on his computer and software. Because I had purchased an out-of-state, he tried another N75 and it also didn't work. I messed around, researched again and then checked all the fuses. I discovered the F10 fuse had blown and replaced it. The boost was back for another 24 hours then it went out again. The wiring must have worn more and the short contact increased. I put in another fuse and the boost was back for about a mile. Now, the fuse blows as soon as the car is cranked. Oh, I also checked the relays after reading that I just needed to run some current to get the solenoid to click. I just used a 12 volt transformer running some mamps for a small electrical device (I have several boxes full of transformers from old telephones, answering machines, routers, etc.) The new N75 clicked when I ran a few mamps at 12 volts. The old N75 was dead.
Going to oilhammer's suggestions... thank you! I like your suggestion with the light. There is obviously more than 10 amps being pulled. Being ignorant on electronics, I'm a bit concerned with plugging in a light that will draw more than 10 amps. I'm thinking that the F10 fuse wiring possibility goes to the ECU because the ECU controls the N75. With current flow, does it make any difference where the short is in the wiring? Say before or after the ECU in the wiring. I don't want to pull far more than 10 amps through the ECU in route to the light. The way the F10 10 amp fuse popped when it blew the last fuse I used, I expect the amp draw is pretty high. I have the highest rated CCA battery I could find for my TDI.
I traced the wiring from the N75 and it goes behind the battery box into a large wiring bundle and into the firewall. I looked up where the ECU is located and perhaps the large bundle goes to the ECU. The N75 has two wires, a ground wire, (green with red stripe on the left or the flat side of the plug) and a hot wire on the right (yellow with brown stripe, round side, looking into the plug connector). Looking around the wiring under the hood, there are lots of yellow wires with brown stripes, going to the head lights for example. The F10 fuse (according to the fuse schematics) controls the N75.


https://www.autogenius.info/volkswagen-jetta-2003-2009-fuse-box-diagram/



I went into the fuse box also but did not check underneath. I pulled all the fuses, checked the relays, and pulled the top cover off the to examine where the fuse terminals connect. It all looked clean and pristine. The connections appear to be on the front side of the fuse box and easily visible. All look clean with no corrosion.


With all the above being said, I think I will crawl around underneath the car again to shine a light and wiggle any wires I can see around the clutch housing, egr cooler, X-frame and dog bone. Then, I may try the light trick.


Please reassure me that I will not fry the ECU with the light trick and I'll go for it too.


Thanks much! Tooth Collector.

Found short! (one short)...

OK, I found a short in the wiring harness directly at the plug going to the sensor (just like you all suggested at the outset... to check the wiring at the plugs). I repaired and the codes cleared. With a new F10 fuse, I can drive with boost and no codes thrown. However, when I stop the car and restart the engine, the fuse is blown and I have codes. Now, I'm wondering if the sensor is also bad but I don't know the name of the sensor to ask a question about the sensor.... and I haven't figured out how to insert a photo so someone can identify.


Toothless

Apparently it was not a sensor, someone posted that it is a heater on the CCV breather tube to keep ice from forming in the tube. The part is 1J0906391B and there's a thread on the TDIClub forum regarding the part. So, if it's a heater, I think the F10 fuse is still blowing even though the wiring is fixed because the heater itself may be shorted. I have unplugged because according to the thread elsewhere on the forum states that it's not connected to the ECU and I'm in the south were I don't have to worry about vapor freezing even in the winter. If I'm correct, by unplugging, it will not short and the F10 ten amp fuse will not blow. I'll post if it doesn't blow the fuse and the boost problem is corrected for codes P0243, 0245 and 2426.
Going for Toothy