ECM Relay Harness...almost there!!!??? (was cranks, won't fire...) [Archive] - - Nissan Sentra Forum

: ECM Relay Harness...almost there!!!??? (was cranks, won't fire...)

11-16-2005, 11:36 PM
First off, thanks again for all the help thus far. Got the car started by doing some creative wiring of the ECM relay harness! Now, I've got to get it right so my friend can drive again! Poor girl!

Anyway, I'm pretty sure that there is a short in the wiring going to the ECM relay harness. Either that or it's wired incorrectly and worked anyway up until a few weeks ago. With this car (2000 Sentra), I can believe almost anything!

So the relay is a single trigger, double throw. That is, terminal 1 gets 12 Volts that pass through terminal 2 (which I suppose goes to ground somewhere!). When that happens, terminals 5 and 3 get closed, and terminals 7 and 6 close. I'll try a little ASCII art here...

1 ----- 2
5 7
3 6

I can't get that to turn out exactly right. 5-3 and 7-6 should be centered...

Anyway, right now terminals 1 and 3 are both getting about 4.58V. They are supposed to be getting 12V (battery voltage). So...there's not enough juice to even power the relay. The voltage is the same, on or off. I tested the relay on the bench and it works great.

Terminal 6 has 12V, all the time, but I'm not sure when or how much voltage it's supposed to have! That's actually how I got the silly car to run, was to pull the relay and jump from 6 to 5 and 7, effectively giving 12V to both sides. The check engine light came on like it's supposed to and she started right up (man the brakes were rough after sitting!)!!!!!!!

There was also no resistance between 1 and 3. I'm not sure if there is supposed to be, though.

Well, I've been hitting the TSM hard, but I can't find much more than what I've said, as far as voltages. Definitely nothing about Ohms resistance and such. I'm sure hoping somebody has some inside knowledge about the relay/harness, and more importantly if this turns out to be a short, about a probable location of the short!!!!!!!

Thanks again, in advance. If you need (or want!) more info, please let me know!!!

11-18-2005, 04:08 PM
Gee...that was a long post...sorry about that.

Basically, does anyone know what the voltages are supposed to be going into the ECM relay? Then...does anyone know where a likely location for a short going into it would be?

Thanks, all the best!


11-18-2005, 05:51 PM
If you are not getting FULL 12V at ECM relay terminals 1 & 3 to ground then it sounds like a loose connection. Check for power at the ECM terminal 67 to ground. What do you get? If it is the same amount of DC Volts that you get at your relay then the problem is more up stream to the fuse. OK lets stop there and see what ya get. Ohms glad that you mention it. It is a great tool on your meter to troubleshoot loose, open and dirty connections. First to make sure your meter is working right test it out. Turn it on and turn to the OHMS setting, touch your meter leads together. What do you get. It should be close to 0.0 ohms it might go up to 1-5 ohms. Make sure you donít see any K or M after the number. K = 1,000 ohms and M = 1,000,000 ohms. Check your connection at the ECM Relay and the load side of the 36 fuse (output/terminal 6U at the fuse) with the battery disconnected and no fuse in. What do ya get. I got to get going. This should get you busy. Post or PM me if you have questions. I am a Electrician in the navy for 5 years and more time before that so I got some knowledge about troubleshooting and so on.

11-18-2005, 10:00 PM
Terminal 6 gets it power from fuse 34. 12V

You said

"There was also no resistance between 1 and 3 I'm not sure if there is supposed to be, though"

Now is that the relay or the wiring harness? If it is the relay, ok that good, if it is the relay wiring harness, some where it is bad.

11-18-2005, 10:36 PM
jcrow...thanks so much for the very detailed response!!! Actually, I'm in my 5th year in the Air Force. Very nice to talk to you!

Tomorrow I will go out and test all this out. However, I can tell you that the voltage at 1 and 3 is the same on the harness. So I agree...something's up.

Anyway, thanks again. I'll post more tomorrow!


11-19-2005, 01:24 PM
OK, so here is some updated info... I grabbed a few pages from the EC section of the TSM. It's for diagnosing power supply for the ECM. I also did what you wrote we go!

1) ECM 67 to ground = 0V
2) ECM 67 to ground = 76.6 ohms...
3) Per the manual, checked ECM grounds 48, 57, 106, 108. Only 57 was good!

4) 36 Fuse (6U) load side to relay 1/3, no battery, no fuse = O.L. Open.
5) Same WITH battery = 1.7V
6) Same WITH battery, HOT side = 280 ohms

reconnect fuse/battery...

7) Relay Term 1 to ground = 1.7V
8) Same to gnd, no fuse = 1.7V
9) T# 6 to gnd, with fuses = 12.5V


So, a change from the last time I checked voltages is that Relay terminals 1/3 to ground have now dropped from 4.5 or so to 1.7V. I did put a battery charger on the car today.

I'm going to print out the grounds for the car and start checking them. Following the FSM, I checked Power Supply-I (PS-I) (PCM term. 43 to ground, ign. on), and got battery voltage. It then skips you straight to checking grounds. Sure enough, only one of the 4 ECM grounds checked out (57), even though on the wiring diagram, it looks like 48 and 57 share a ground.

So...I hope that you all can make sense of this. Like I said, I'll starting checking grounds and see what I can find.

Again, thanks soooooo much. Maybe we can get this thing going after all!


11-20-2005, 07:58 AM
Your ohms reading seem high. There is a connector under the air box. It is gray and has 8 wires going threw it. Check it out make sure it is not loose or dirty. The wire from fuse 36 goes threw it to get to the ECM and the ECM relay. You can check and see if you are getting 12v to that harness. If you are getting 12V, check the wire that goes from that harness to the ECM wire terminal 67 in Ohms with out power and see what you get. Somewhere after that 8 pin connector there a splice in the wire that goes to the ECM relay that might be where the problem is. On the FSM page PG-27 it shows connector E9 (E9 is the wires coming from the battery) as being the right side with the wires going to the left into the connector underneath the air box.

As far as your grounds I don't know what is going on there. In the FSM it show the picture with all the pin number for the ECM harness as if you were looking at it threw the back where the wires go threw, are you checking the grounds with the harness disconnected and putting your meter leads from the back of the harness to the pin number?

I hope this helps


11-22-2005, 07:04 PM

Well, GREAT NEWS!!! Thanks to all your help, and especially, thanks to jcrow. I was typing up some new readings, and getting closer and closer. Finally I just stopped typing and started working my way back from the gray connector near the airbox to the fuse box. The break/bad connection had to be between the fuse box (engine bay) and the connector, because the connector to the relay worked great. So...I took a chance and pulled off a section of loom and tape very near where it takes a dive down to the bottom of the radiator.

I was chasing a white wire w/ blue trace. I found it, and lo and had a worn-out spot in it!!! It had worn, or corroded, or somethinged, right through. I spliced in a little wire, and PRESTO!!! She's running like a top! Now, I've still got to fix the blower, and it's still giving a code, but heck, it's running!!!

Again, thanks so much to all of you that helped out. Joey, the Navy must have a pretty good electrician working for them!

Take care,