2001 300GT V35 VQ30DD mysterious current draw

[dcbrett]

Hi everyone, really hoping someone can help me with an issue ive been having!

Ive been battling this for a while not with my 2001 300GT (VQ300DD). I have a constant current draw on my battery which drains it if I leave the terminals connected for a more than a few days, battery seems fine if I just unplug it whenever im not using it

I disconnected negative terminal and measured current draw across the battery with everything off and it is ~400mA. I understand this should be closer to ~50mA.

I trawled the internet for wiring diagrams and the only one I could find was a Russian version, ive attached a screenshot below and labelled what I think are relevant sections.

I pulled fuses and discovered the issue with the 15A fuse that controls quite a few components.. From the fuse I went to the relay labelled 1 located in the IPDM cluster and put a jumper across coil terminals first and then relay terms.

I discovered that the fault was on the relay circuit and not the coil circuit, this lead me to believe that the issue could lie with the components labelled as group 3 below. Im realising now that group 2 is off this circuit as well which I haven't checked..

Group 3 consists of MAF sensor, camshaft position sensors and crank shaft sensor. I pulled all the wire harnesses on these but did not see any change in current draw so concluded these to not be the issue.

I then unplugged the ECCS labelled 4 and the current dropped to ~130mA

From here Im not too sure how to proceed, does this mean my ECU is bad or could it be any other device connected to the ECU?? Im reluctant to buy a replacement ECU before being certain I know where the fault lies.. Im also curious as the current draw is still slightly higher than expected..

Any help would be greatly appreciated!

Thanks in advance!

[GTSBoy]

I'm not sure how different these Renault afflicted Nissans are compared to the proper ones, but it would seem as though perhaps there is a fault with the ECU and/or the ECCS relay (which is triggered to turn the ECU on and latch it on when the ignition is ON) causing it not to turn off.

[sonicii]

As above, I would be looking into why they relay is engaged when the ignition is NOT on.  If there was supposed to be full time power on this circuit, why have a relay there?

400mA may be perfectly normal when that relay is engaged and not indicate a faulty item supplied by that relay.

[dcbrett]

15 hours ago, GTSBoy said:

I'm not sure how different these Renault afflicted Nissans are compared to the proper ones, but it would seem as though perhaps there is a fault with the ECU and/or the ECCS relay (which is triggered to turn the ECU on and latch it on when the ignition is ON) causing it not to turn off.

Interesting! I wasn't aware of the Nissan / Renault relationship.. Is this why I cant find an OBII scanner that will work on it?

I found wiring diagrams for a 2003 350GT and it appears the ECCS relay is energised at all times (as long as battery is connected).. please correct me if im wrong. Ive also pulled the relays out and put voltage through them to ensure they are pulling correctly. 

 

[dcbrett]

14 hours ago, sonicii said:

As above, I would be looking into why they relay is engaged when the ignition is NOT on.  If there was supposed to be full time power on this circuit, why have a relay there?

400mA may be perfectly normal when that relay is engaged and not indicate a faulty item supplied by that relay.

Yes this was the source of much confusion! but as above I believe it is energized at all times.. unless I'm reading into things incorrectly.

There are 2 relays of the same make in the same board and I switched them over to see if it made a difference but no luck.

I might post elsewhere on the forums to see if someone with the same car make could check what current draw they are getting.

[Duncan]

I don't have a suggestion on the draw overall, but per the diagram 2 pins on the relay will have12v at all times. One pin will have earth when the ECU wants to turn itself on. The other pin will have 12v only when the ECU earths the third pin.

So, with the car off, relay out, the holder should have 12v at 2 pins, nothing (neither earth nor 12v) at the other 2 pins. If you have earth at one of those 2 pins (and 12v at 3 of them with relay in) either the relay failed, there is a wiring problem where the signal wire is touching earth, or a problem in the ECU where it either thinks it is meant to be on or it has failed somehow

[sonicii]

when you pulled the ECCS connector, do you still have 12V at pin 31 of the IPDM, if you do, this suggests a problem with the relay (which you probably eliminated by swapping relays), or a wiring problem between IPDM pin 36 and ECCS pin 31.  ( I hope those pin numbers are correct, they are a little hard to read).

As Duncan mentioned if you have a short to ground on that wire, it will keep that relay engaged all the time.

Edited April 8 by sonicii

[dcbrett]

On 07/04/2024 at 9:52 AM, Duncan said:

I don't have a suggestion on the draw overall, but per the diagram 2 pins on the relay will have12v at all times. One pin will have earth when the ECU wants to turn itself on. The other pin will have 12v only when the ECU earths the third pin.

So, with the car off, relay out, the holder should have 12v at 2 pins, nothing (neither earth nor 12v) at the other 2 pins. If you have earth at one of those 2 pins (and 12v at 3 of them with relay in) either the relay failed, there is a wiring problem where the signal wire is touching earth, or a problem in the ECU where it either thinks it is meant to be on or it has failed somehow

 

On 08/04/2024 at 6:33 PM, sonicii said:

when you pulled the ECCS connector, do you still have 12V at pin 31 of the IPDM, if you do, this suggests a problem with the relay (which you probably eliminated by swapping relays), or a wiring problem between IPDM pin 36 and ECCS pin 31.  ( I hope those pin numbers are correct, they are a little hard to read).

As Duncan mentioned if you have a short to ground on that wire, it will keep that relay engaged all the time.

Thanks for this advice guys, yes I have swapped the relays to rule out a fault with the relay itself. I have just recalled that my IPDM circuit board was refurbished recently because it was basically submerged in leaves and gunk. I will investigate this further.

Other research I have done in the meantime - I used a clamp ammeter on all the wires coming out of the back of the ECU and some draw does appear to be on the control unit power supply. Does this further confirm a problem with the IPDM board or still possibly the ECU? I feel like the IPDM might be the most likely culprit.

("ground" and "weight" appear to have similar translations in Russian).

I will run further tests on the IPDM and relay contacts when i get a chance.

Cheers all.

 

Edited April 14 by dcbrett

[sonicii]

I would be starting with this wire, when this is grounded, it engages the relay that supplies power main to the ECU and a few other items.

I suspect this relay should NOT be energised when the ignition is turned off.

Either the ECU is faulty and is grounding this pin on the ECU full time, or there is a short to ground somewhere between the ECU connector and this relay.

Pull the relay and use a multimeter on ohms between pin 36 (I think it is 36) of the IPDM and ground, you will likely measure near enough to zero ohms.  Unplug the ECU and check again between 36 and ground, if it is now open, it is likely the ECU at fault, or something telling the ECU the ignition is still on, if you are still measuring something similar to the first measurement to ground, you probably have a wiring problem.  If you can unplug the IPDM, do that, if you still measure low resistance to ground at that relay connector, the issue is in the IPDM, if you are now measuring high or infinite resistance, the issue is in the harness.