I've been working this one for a year now and it's got me beat. I even admitted my defeat and took it to the dealer but they diagnosed this wrong. I got 6 months before I need to smog and I'm all out of ideas.

I've been getting codes P0400 (EGR flow), P0443 (Evap purge ctrl) and P0500 (speed sensor A) in various combinations.

I checked the Evap purge volume control valve - OK 43ohms on each winding, purge control valve (clicks when powered.) I checked the EGR control solenoid (clicks when powered), EGR valve (can hear valve open/close with vacuum applied).

The dealer agreed with all this and said I needed a new ECM. Not having that sort of cash lying around I checked out my ECM and sure enough there was some corrosion around pins 117,118,119 and also along that edge of the PCB. I cleaned it all up, resoldered all suspicious pads and replaced. Same deal.

I bought a used ECM and even managed to match the P/N's exactly. Same deal.

Today I went and ohmed out all the sensor wires in the harness and everything is connected and sound.

The only thing I haven't completely verified is the speed sensor. The FSM shows the speed sensor as having a 2pin connector. Mine has 4pins. Am I looking at the right part? The speed sensor I'm looking at is on the lower side of the transmission. I used it to drain the tranny when I did the CV's. This is the speed sensor right?
Anyway, I'd have thought a bad speed sensor would have broken the speedometer right?

What am I missing here? What's the common link?
I really hope this isn't an intermittent wiring problem

 

what year? also how long has your speed sensor cel been on? i belive that the sensor is on top of the tranny. at least for a 5spd.

 

Dec 95

 

actually, the speed sensor P0500 is recent since I swapped ECMs. Mebbe a coupla weeks

oh and yes, 5sp

 

Check the continuity of said wires while moving the harness around where it bends near the right strut tower; there was a TSB about this, intermittent wiring problems.

 

Thanks Pmohr!
I'll try that

 

Sensor at bottom of tranny is neutral switch. That explains the connector. Let's see if today is my lucky day!

 

You mean the harness here where it goes from engine to body?

All connections are rock solid

There's got to be a common link between these parts. I can't believe 3 parts failed at once.

I read somewhere there's a temperature sensor that is used to detect EGR flow. Does this have any effect on evap purge?

Any ideas greatly appreciated - I'm dead in the water.

 

I checked the EGR temp sensor and it looks good 2.6Mohms at around 70deg F. Even measured at the ECM connector.

Reset the ECM. Last CEL was P0443 on its own. I'll see what it throws up tomorrow.

Maybe all this plugging and unplugging will scrape enough cr@p off the contacts to make it magically work properly.

What's nissan part number for voodoo juice?

 

I want some voodoo juice too...I hate my car right now. But at least yours runs...haha.

Another thing to try might be to remove the ECU cover plate, and plug in the ECU harness, and test continuity from the wires to the pins inside the ECU.

 

I've wondered about that. But in the end I decided against it because the ECM might need to be grounded to the chassis through the mounting bolts. You'd have to pull the ECM out from under the center console to be able to probe it.

I guess I could install a temporary ground, bolted to both the ECM case and the chassis. Then I could start looking at what the ECM is seeing as I drive around.

Better make it hands free!

 

Hahahaha. Nice.

I dont think it is grounded. Although its possible, I think that the 6 grounds going into it already are what it uses. I could be wrong though.

 

The mounting bolts do not act as a ground FYI.

 

......2 days, 4 trips, 50miles, 70%freeway (although I can't tell the difference around here)

still no CEL.......


You guys, you sent some voodoo juice didn't you

 

5 days and no CEL.....

So it would seem that I didn't need the new ECU. The problem was corrosion in the ECU wiring harness connector. Thanks Pmohr for putting me on the path to resolution!

So the dealer would have put in a new ECU ($1500) to no avail, then installed a new harness (that's got to be an expensive and labor intensive job - $2000??). I bet they wouldn't have refunded the cost of installing the unnecessary ECU.

I reckon I saved myself over $3K. Guess I can afford gas now