N75 short to ground fault?

[RobDon]

Shortly after getting my car running superbly, I am now getting a fault code for the N75 - short to ground and it appears to be in hard limp mode, will only boost to 0.5 BAR?

I don't even use the N75, it's plugged in but not attached to anything - anyone had this before and is the only solution to replace the N75 or can I just fit a 330ohm resistor?

I have moved the N75 and wrapped it in rubber tape, but code is still there.

 

[DodgyDave]

Can you not try to remove it (un-plug the N75), clear the codes, then go for a drive .... if the error does not come back it's the N75 ??

Guessing that with it un-plugged it'll throw up another error, but that will let you find out if it's the wiring or the N75 thats causing the codes.

Just an idea


ta, Dave

 

[RobDon]

Yeah I'm going to unplug it and go for a drive, see what happens. It's annoying as it has sat there for 4 years and suddenly I get this code just when things are going right!

 

[jivejester]

330ohm will do the job, had exactly the same problem as you.... and the 330ohm did the trick.

 

[RobDon]

Great, thanks for that, I was hoping that would work.

I've just finished fitting one so will go for a drive this afternoon, hopefully it's fixed. I didn't want an 'open circuit' fault so I fitted the 330ohm 10-watt resistor.

 

[RobDon]

Ok that didn't work, still got the short to ground fault. But things have gotten alot worse now, car is cutting out at junctions, there were 2 big backfires and it struggles to make any boost beyond 0.5 BAR. I now have 5 fault codes!

17955 - boost pressure regulation valve (N75): short to ground
17705 - pressure drop between turbo and throttle valve (check DV) (most likely the turbosmart)
16395 - bank 1: camshaft A (intake):retard setpoint not reached (over-advanced)
16705 - engine speed sensor (G28): implausible signal
17584 - bank 1: o2 (lambda) correction behind catalyst: control limit reached (turbosmart probably)

I've gone from no fault codes to all those! Anyone any ideas - has my exhaust manifold cracked and is blowing? I noticed recently I had to increase the wastegate duty cycle for it to reach 1.4 BAR but it wasn't holding it very long, which it didn't do before.

 

[DPJ]

I'd guess that's an electrical/wiring problem, Rob - ECU /N75 related? (one thing causing them all)

 

[RobDon]

Not got a clue m8, I haven't touched anything electrical for a long time.

 

[RobDon]

Anyone know the part number for the engine speed sensor and where it is located on the engine?

 

[barnsley]

dont know the part number but its near the oil cooler but in the engine block gearbox side

 

[DPJ]

dont know the part number but its near the oil cooler but in the engine block gearbox side

Yeah I agree. Possible knocked connector, Rob?

 

[RobDon]

Yep, something is wrong with it, after searching on Vortex most of the codes I have relate to a knackered G28 speed sensor. I asked Star about the fault codes and that was the first thing Jim said - right on the money! They're ordering a new one and fitting it for me. Part number is 06A906433L.

 

[RobDon]

Ok weird things going on with my car. Star changed the crank sensor this morning, now the car won't start at all!!! I drove the car up there this morning, no problems, started first time. After changing the sensor the car started first time. When Brian went to take the car for a test drive - it won't start!!!

After checking all the earth points, changing the plugs etc. still nothing.

 

[RobDon]

Ok after searching on Vortex it seems that a faulty fuel pump relay can cause faults such as the short to ground fault and also non-starting.

 

[RobDon]

Found the problem - corrosion on the relay board, so a new relay board has been ordered and will be fitted tomorrow.

 

[cuprabaz]

Good to see you got to the bottom of it Rob.

 

[RobDon]

It's not over yet. Star have fitted a new relay board and fuel pump relay and car started 6 times no problem. But it's now playing up again, sometimes it will start sometimes it just cranks over.

Anyone any ideas?

 

[cuprabaz]

Are you 100% that all the earths are clean and tight? And that all the cables have no splits.

I've give all the contact points a good rub with steel wool or a wire brush just to make sure.

 

[RobDon]

Already done all that Barry. All earth points have been cleaned and re-tightened, tried different spark plugs, different coilpacks, new relay board and new fuel pump relay. Next thing to try is to bypass the Walbro pump and see if that is causing any issues. Another thing to try is a new coolant temp sensor as this can cause non-starting and boost issues as well.

 

[DodgyDave]

Rob, when i had issues with my coolant temp sensor it was always starting OK, but causing boost & limp-mode (due to overfueling getting picked up in the lamda sensors).

Do you have a fuel pressure meter, i think i remember you getting one ages back but not sure as your car changes a lot - this would let you know if the fuel is getting to the engine or not....

Dave