Radiator Fans, ECU Fuse Blows

[Sailor96]

Problem for you gents,

Driving around running really well, not in a limp mode condition, but the fans weren't switching on and temps were rising dangerously above normal

I tried using nistune to diagnose the problem and couldn't connect through the consult cable initially. Found the 10A fuze was blown for the ECU (bottom right 4th up).

Managed to connect to the ECU with a higher amperage for only a moment, didn't see any temp sensor faults.

Disconnected the fans and put in another 10A fuse and it still blew.

New OEM Nissan fan relay I just installed last weekend and the fuse still popped.

Anyone had this issue before? TIA

 

[Luke1134]

Hello,
I haven't had this issue before but looking at it from a wiring point of view if this is the fuse that is blowing for you then you have a short to ground on this wire or potentially within the S.M.J or up to the relay, as this fuse is getting its supply from the ignition switch and is grounded from through the relay coil, if that fuse is blowing then it should be a short to ground on that live wire. I wouldn't recommend using higher amperage fuses as this runs the risk of fire with a short, if you don't want to go tracing through the loom/wiring to find where its shorting the easiest thing would be to cut that wire and run a new one, which will save you alot of time but if this is shorting with other wires then you could have further issues and will have to find and trace as to where its shorting. There is a potential for the fuse box itself to be shorted on that fuse also but a quick continuity check with the fuse removed should confirm the fuse box ok.

 

[Sailor96]

if this is the fuse that is blowing for you then you have a short to ground on this wire or potentially within the S.M.J or up to the relay, as this fuse is getting its supply from the ignition switch and is grounded from through the relay coil, if that fuse is blowing then it should be a short to ground on that live wire.

I verified continuity at the fuse box and there was no continuity, so the fuse box is okay.

I ran another test from the outlet of the 10A to the fan relay, which had continuity through the wire.

Then from the same relay to body ground and it also had continuity, which if I'm not mistaken is a unwanted short?

I'm trying to find the connector at the moment to see which side of the connector the short is on to narrow it down a bit

On a side note. The manuals circuit diagram labels the relay as the "fuel pump relay", but the "rad fan1" relay has the correct corresponding wire colors and has been the one I've taken all the tests from. But overall has been a confusing conflict of information

 

[Sailor96]

More confused now then ever

Disassembled the SMJ separating the two connectors. The engine side has the male connector pins, the interior side female.

Tested between the 10A and SMJ C4 (female), all good and not grounded.

Tested between SMJ C4 (male) to Rad Fan1 relay, again all good and not ground

I can't help but think it might actually be the fuel pump relay... But the wire matches the diagram with W/G(white green stripe) and L(blue) on the coil side of the relay. The SMJ C4 location seemed off, but the same white green wire came off the male side that I tested

 

[Cathode]

i wish i could help you but it's all witch craft to me.

 

[Luke1134]

Sorry for the delay in getting back to you haven't had a chance, so the second wiring diagram gives alot more information, continuity isn't really the best test to do for a short as there can be continuity through the ecu/sensors/etc and can lead you down the wrong path and completely confuse everything and even at times cause damage as during the test inputs a small amount of voltage to test and this can "blow" ecus but the test can offer assistance here. Don't focus on the fan relay or the fuel pump relay focus on the fuse side of things so this wiring diagram shows another connection on this cable that is the 12v supply from the fuse and with this disconnected from the SMJ you can do a continuity test to ground and see if that it "beeping" which with a short to ground it will but also will if its earthed through a sensor/ecu, so if you have the other side of this diagram follow on to see where that fuse also supplies as the short to ground could be on that side of it also. As current will take the least path of resistance and if there's a short on the other side of the wire the current wont go through the SMJ to go on and power up anything it will go straight to the short to ground and pop the fuse.

 

[Sailor96]

I've been using the FSM for the drawings, I have a link to it compiled for RNN14 only which is a searchable document

Pulsar GTI-R RNN14 Full Service Manual.pdf

drive.google.com

Most the electrical is on the last few pages, it's hard to fit it all into one cropped photo

 

[Luke1134]

Ill have a look and see if i can trace it back, just have a look under the bonnet to see if there is any visible shorting/chaffing/rubbing of the engine loom anywhere, around the body/engine components alternator etc, and ill see what i can find on those diagrams

 

[Sailor96]

focus on the fuse side of things so this wiring diagram shows another connection on this cable that is the 12v supply from the fuse and with this disconnected from the SMJ you can do a continuity test to ground and see if that it "beeping" which with a short to ground it will but also will if its earthed through a sensor/ecu, so if you have the other side of this diagram follow on to see where that fuse also supplies as the short to ground could be on that side of it also. As current will take the least path of resistance and if there's a short on the other side of the wire the current wont go through the SMJ to go on and power up anything it will go straight to the short to ground and pop the fuse.

Thanks for the reply

I took another look at the drawing. That leg goes directly to the consult connector pin and terminates.

Here's my thought process at the moment:

With the 10A fuse out, SMJ disconnected and no diagnostic cable attached there should be no ground to body (W/G wire)

On the other side of the SMJ to the Radiator fan relay plug E60, with the relay removed, there should be no ground to body (W/G wire)

From the radiator fan relay plug E60 (L wire - blue) to EFI harness plug F10 there should be no ground to body

With the ECU disconnected, from the EFI harness plug F10 to the ECU terminal block F31 there should be no body to ground

If there are no grounds found in any of the above circuits, it's internal to the ECU

 

[Sailor96]

 

[Sailor96]

Ill have a look and see if i can trace it back, just have a look under the bonnet to see if there is any visible shorting/chaffing/rubbing of the engine loom anywhere, around the body/engine components alternator etc, and ill see what i can find on those diagrams

I appreciate all the help, I'll take a look again today

Also let me know if that document link works, it should be open to the public

 

[Luke1134]

Thanks for the reply

I took another look at the drawing. That leg goes directly to the consult connector pin and terminates.

Here's my thought process at the moment:

With the 10A fuse out, SMJ disconnected and no diagnostic cable attached there should be no ground to body (W/G wire)

On the other side of the SMJ to the Radiator fan relay plug E60, with the relay removed, there should be no ground to body (W/G wire)

From the radiator fan relay plug E60 (L wire - blue) to EFI harness plug F10 there should be no ground to body

With the ECU disconnected, from the EFI harness plug F10 to the ECU terminal block F31 there should be no body to ground

If there are no grounds found in any of the above circuits, it's internal to the ECU

Yes correct that wire from the fuse going to the SMJ and the diagnostic cable should have no ground this is where the continuity test helps when everything is disconnected, the concern from looking at it is the supply line to the relay plug so the line after the relay in the below pic I feel could not be the cause as the current would be passing through the relay to get to the short which is still a possibility and an interesting check would be to have the relay out replace the fuse if the fuse pops with the relay out then you could confirm its not on that line as there would be no way for the current to pass through if the relay is out. Finding shorts is never the easiest and is just a process of elimination and unfortunately takes time, now i know putting in another fuse risking it to blow it not the best way of testing this but it can be quick to determin if it is on the side after the relay or not, you can also plug out the harness from everything and then do a continuity test to ground which will help to confirm but you must have the connectors disconnected for it to be accurate. If the fuse does not pop with the relay out then you could presume its on the other side of the circuit and when the relay goes back in the relay will click and the fuse will pop, again its a very crude way of doing it or you can do the disconnects and test

 

[Sailor96]

Lot's of testing wires today, still inconclusive. I went and disconnected every plug associated to the diagram for the radiator fan relay, checked continuity between every terminal, and they were all good. I even opened the ECU to see if I could spot any damaged pins or broken solder connections, referencing the Nistune v3 install guide even to see what changes to the original board even. The only thing noteworthy was two pebbles inside the ECU casing. I feel it's unlikely the cause of a persistent fuse popping. Tomorrow I may try to put it all together again and try it without the relay installed, I thought I had tried it beforehand but simply forgot to mention it in previously

 

[Luke1134]

Lot's of testing wires today, still inconclusive. I went and disconnected every plug associated to the diagram for the radiator fan relay, checked continuity between every terminal, and they were all good. I even opened the ECU to see if I could spot any damaged pins or broken solder connections, referencing the Nistune v3 install guide even to see what changes to the original board even. The only thing noteworthy was two pebbles inside the ECU casing. I feel it's unlikely the cause of a persistent fuse popping. Tomorrow I may try to put it all together again and try it without the relay installed, I thought I had tried it beforehand but simply forgot to mention it in previously

Interesting to find some pebbles in there but I do agree that shouldn't cause the issue unless it was some conductive material that could have already potentially blown the ecu.

Just looking at it from the wiring point of view, if nothing really changed and the issue happened out of nowhere I would be looking at the wiring in the engine bay side of things like the below image, as I said the highlighted line is the line thats causing the fuse to blow as its being shorted, now weather thats being shorted to ground through a break in the loom shorting to body or after chaffing together with another part of the loom and earthing through a sensor is the toughest thing to find.

Once you try it with the relay out that should give you a better indication, if it pops with the relay out then it must be the line highlighted red below, weather its in the engine harness or in the interior harness would be the next thing, so if the fuse pops what I would do instead of physically inspecting the whole wire all the way back, you could cut the wire (leave enough space to add on a connector) and run it to the side of the relay you want it to go to the same if its the yellow wire below, from what you've said with the testing you've done, the fuse won't pop with the relay out and when you put the relay in it will pop the fuse to indicate the fault is on the yellow line.

Thats going off the information that from the SMJ C4/C5 to the relay input of 85 (coloured red wire in below pic) with the relay disconnected and the SMJ plug disconnected there was no continuity between this wire and ground, and same from the wire going into the SMJ from the 10A fuse with the fuse out and SMJ disconnected there was no continuity between this wire and ground.

Hopefully the end will be in sight for you after today

 

[Sailor96]

Hopefully the end will be in sight for you after today

Re-plugged all the connectors today, removed the radiator fan relay and the 10A fuse still blew. Damn Also double checked the fans and temp sensor by disconnecting the plugs as a shot in the dark, no luck there either. Seems the pebbles were in fact not at fault here lol

Thinking about it more it could be the temp sensor itself, or rather the wiring, as when I first purchased the vehicle I had to make some repairs to the wire harness for it. Maybe through the ecu the switch for the temp sensor is shorting thus shorting the fan relay fuse? I will take the intake manifold off after work and confirm this circuit is still functioning properly. Usually it would throw a code for the temp sensor if it had faulted, which I mentioned early on I briefly managed to hookup to the ecu with a computer and read no codes just before the fuse went (with a 30A)

Just so we're all tracking the same thing, the SMJ pin is only C4 as the diagram is split to show for the N14 and B14 models wiring designated by the "(N)"

Did you mean to attach a photo? If so I can't seem to view it

 

[Luke1134]

Did you mean to attach a photo? If so I can't seem to view it

Apologies I never attached the pictures, they should be attached now and the Red line is where the fault is, as with the relay out the fuse still popped which to me indicated that the fault is not passed the relay as no current can pass through with the relay out, this again would say the ecu is not at fault as the relay is earthed through the ecu and with no connection to the ecu the fuse still blew.

Which would also throw out the temp sensor being the culprit as the temp sensor is wired to the ecu and the ecu will use an independent transistor to ground the fan relay to turn it on, in theory yes the coolant temp sensor and ran relay are connected but in reality they're not as the ecu uses the information form the temp sensor to make a calculated decision to ground the relay and turn it on theres no physical connection within the ecu for these.

Looking at the diagram ive highlighted the exhaust gas sensor which is a good culprit for this to be your short, as the loom could have melted to the exhaust and this would cause your short to ground and pop the fuse. You had a 30A fuse in place of the 10A (to connect to the ecu) I wouldnt recommend doing this as 30A of current (which popped the fuse again) is far more than what the initial wiring is rated for 10A so this could cause a fire if you tried it again for connecting purposes, I would be looking at the loom from the lambda sensor from the highlighted line below, the fault is on the red one just where is the thing, and for me the one that makes most sense is the lambda sensor as this is next to the exhaust

 

[Sailor96]

Looking at the diagram ive highlighted the exhaust gas sensor which is a good culprit for this to be your short, as the loom could have melted to the exhaust and this would cause your short to ground and pop the fuse. You had a 30A fuse in place of the 10A (to connect to the ecu) I wouldnt recommend doing this as 30A of current (which popped the fuse again) is far more than what the initial wiring is rated for 10A so this could cause a fire if you tried it again for connecting purposes, I would be looking at the loom from the lambda sensor from the highlighted line below, the fault is on the red one just where is the thing, and for me the one that makes most sense is the lambda sensor as this is next to the exhaust

That is a very good catch, the drawing has it going to the consult for B13 series which I ignored. Not noticing that it also ties into the exhaust temp sensor! This must be were the fault lies, if not wiring then a shorted sensor (or maybe both, especially now since it's seen 30a )

I'll have to inspect the sensor and the surrounding wires. I'm sure there is a resistance check for the sensor itself, so I should be able to determine if it's faulty. If I don't find anything obvious I might have to disconnect the SMJ again to retest the engine side loom

I'll update the tread once these have been checked, cheers

 

[Sailor96]

This was a massive oversight on my part. You were absolutely right @Luke1134, I unplugged the lambda sensor and tried a new fuse. SUCCESS! No more blown 10A fuse. I then warmed up the car (which took a little bit as it's getting colder here) and the fans kicked on and off when they were supposed to.

No visual damage to the wires or sensor that I could see so it must be internal, or at least that's my running theory. New sensor is on order

I can't believe the solution was so incredibly simple, and of course now looking back it seems like the obvious culprit

 

[Luke1134]

This was a massive oversight on my part. You were absolutely right @Luke1134, I unplugged the lambda sensor and tried a new fuse. SUCCESS! No more blown 10A fuse. I then warmed up the car (which took a little bit as it's getting colder here) and the fans kicked on and off when they were supposed to.

No visual damage to the wires or sensor that I could see so it must be internal, or at least that's my running theory. New sensor is on order

I can't believe the solution was so incredibly simple, and of course now looking back it seems like the obvious culprit

Brilliant I'm delighted you found the issue, when it comes to diagnosing wiring alot of people dont want to even try to start so fair play to you for sticking at it and finding the issue, the older cars were great for this the newer stuff is alot different where you dont have as many fuses you might have a signal sent from a control module to another control module to activate the other control module which is where the oscilloscope comes in handy, could indeed be internally if theres no visible breaks/chaffing points on the loom going back and with the sensor disconnected it doesnt pop the fuse but that could also indicate the fault being on the other side of the loom/output of the sensor, to confirm this you can do further checks to the output side of the sensor loom, to make sure the sensor was the culprit, which hopefully sounds like it was.