Thread: ECU and Chasis grounds?

(I have no SES light and am doing some testing, also no fuel pump)
All the relays have power and ground.

I uploaded the pinout for the ECU with markers.
So I'm checking my ECU harness and this is what I find.

The good;
Red - pins 109 and 111 both have good 12v sources
Black - pin 108 - Good ground, returns 12 volts

The odd;
Blue - pin 59 ( supposed to be a ground? ) no wire there

The bad;
Green - pins 60 and 106 - Supposed to be ground, return 0 volts when testing

Would I be able to just reground these to the battery myself to solve this issue?

Also where are the grounds located on the car, some people say they have loose grounds, so I replaced the battery ground , but where are all the other ones lol. Any input is appreciated!

Everything on the engine harness grounds on the timing cover. Take some sandpaper to the mating surfaces and see if that helps something

I see 4 bolts, 2 wires to each on the top portion of the timing cover, checked all those grounds and seemed to be good. Any chance anyone knows which one goes to which pin out? I could test the OHMs of each wire, that' d be a great test.

Originally Posted by vexixx

(I have no SES light and am doing some testing, also no fuel pump)
All the relays have power and ground.

I uploaded the pinout for the ECU with markers.
So I'm checking my ECU harness and this is what I find.

The good;
Red - pins 109 and 111 both have good 12v sources
Black - pin 108 - Good ground, returns 12 volts

The odd;
Blue - pin 59 ( supposed to be a ground? ) no wire there

The bad;
Green - pins 60 and 106 - Supposed to be ground, return 0 volts when testing

Would I be able to just reground these to the battery myself to solve this issue?

Also where are the grounds located on the car, some people say they have loose grounds, so I replaced the battery ground , but where are all the other ones lol. Any input is appreciated!

Grounds should not show voltage that would be a bad thing Ground pins should show continuity to ground source "Green - pins 60 and 106 - Supposed to be ground, return 0 volts when testing"

Almost sounds like your ecu could be bad. I had fuel but no spark with no ses. Turned out my ecu quit on me. Something to maybe keep in mind because a faulty ecu can show up as any number of weird problems.

Well I got another ECU from ebay because the dealership said this one was bad. However the one I just got returns the same results.

I'm not checking the ECU itself though but the harness itself.
Why should a ground not show 12v on the multimeter if the positive lead is on the battery?

You went wrong with ebay. Just get one from a partout on here. In fact i have a perfectly good p5 ecu for sale

Don't use an ecu ground to check if it's hooked the the ecu

ECU isn't connected, just checking the harness to make sure I'm getting all the correct inputs.

The ECU was pulled from a wrecked car so I figured it was good , but eBay offers much more security than forum buys ( I've been ripped off on forums before ).

Anyone happen to have a diagram where where ground wires go to, I can do a continuity test on each wire. If I know my harness is good then I know its not the ECU or its a sensor.
Unless someone with a running 03 Spec V SE-R lives close to Paso Robles, CA that can test it ;-) (ECU is a K3)

You have power to fuel pump relay? do you have power out of relay?

Originally Posted by Specv03

You went wrong with ebay. Just get one from a partout on here. In fact i have a perfectly good p5 ecu for sale

Lucas, can you PM me a price on that ECU??
Its a 02-03 Non Nats unit correct?
Thats what i would like to get (then send to JWT for a reflash, i have the TN reflash now)

You can check continuity to any chassis ground location You can download the diagram from here

How much did they charge for the ebay ecu?

Originally Posted by CORN DOG

Lucas, can you PM me a price on that ECU??
Its a 02-03 Non Nats unit correct?
Thats what i would like to get (then send to JWT for a reflash, i have the TN reflash now)

For without nats your going to need either a 5L (2002) or K3 (2003) both have the same pinouts and are interchangeable, but the 5P is for 2002-2003 w/nats

Originally Posted by Jon

You can check continuity to any chassis ground location You can download the diagram from here

There is nothing on my pc after here..

Also I did an ohm reading and as I said earlier the good ground (pin 108) came up as 0.2 all over the car. However pin 60 showed up, but as a whooping 147.2 so there's some series resistance in this line.

The other grounds showed me no response.

Originally Posted by Jon

You have power to fuel pump relay? do you have power out of relay?

I have power to the relay I did not check after the relay.

Nissan Sentra Factory Service Manuals
Download the manual here great trouble shooting info sounds like a ground make sure you are looking at the 2.5 not the 1.8 when you look at manual trouble shooting

The trouble shooting for that board/harness starts around section EC page EC-1326 I think....

Originally Posted by Jon

The trouble shooting for that board/harness starts around section EC page EC-1326 I think....

So after reading through this, the ECM pinout isn't the same as mine.

I've been using this for my ECU harness info so far.
I really need the ecu pinout for a 2003 Nissan Sentra Spec-v. - JustAnswer

If you look at the ECU pinout diagram its completely different, is there a FSM for 2003 sentra spec-v?

Thank you btw though.

So in the end I got my SES light back on.... Although I'm not proud lol..

Anyway so the tech that did the diagnosing didn't replace the ECU relay. When I went to check what I thought was the ECU relay it wasn't, was another relay. The plug for the ECU relay was put back but with nothing in it so I thought it was an unused adapter for a different model.

Still doesn't start, but at least I finally narrowed it down to the fuel pump.