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I have a 2001 Nissan Altima 2.4L
I was tracking down a check engine light and it was a p0303 (cylinder 3 misfire)
I checked everything and got to compression test. That was all great.
Rented a set of noid lights to test the injector pulse from the connector and sure enough cylinder #3 is not getting a pulse signal at all.
I was informed on a Nissan specific forum that if I have power at the connector then it’s most likely my ECU.
How would I test the connector for power? Just hook my Dvom positive test lead to the connector and the other side to an engine ground?
Thanks
**Bonus question. That person also said that if it is my ECU that I’ll have to have it reprogrammed to work with my key. Is this a dealer only type of deal or could I do it with a scan tool? I have a friend that has a couple decent scan tools that I could use
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they way i would approach this at school would be to back probe the connector at the ECU and use a DVOM set to DC volts and see if I could detect a signal being sent from the ECU.
If signal, repair an open in the circuit.
If no signal, re-flash ECU with latest software update.
Just for fun, see if you can get your noid lights to light up on known good injectors; it is theoretically possible that you could have a bad noid light.
K so how i would aproach this is first make sure you have voltage to the injector, normal systems work where they have constant power and the pcm pulses a ground, so if you take your dvom and back probe the fuel injector connector you should see batt voltage. Once you determine that you have the proper voltage verify with your meter that you dont have a ground pulsing. (A easy way to verify that your noid light is working properly test another injector to see if you have pulse, k so before you condem the pcm me in my diagnostic process would proceed to ohm out my pcm ground side, and if that tests out the 1 and final test i would do is perform a load test, (if your pcm is easily acievable and you can obtain a wiring diagram you can skip the load test and back probe the signal wire ( ground pulsing wire) right out of the back side of the pcm and if you see a ground pulse there then you know you have a wire problem if not theres only 2 things it could be a spread terminal or a bad pcm). Sorry im not the best teacher but that is my approach to solving a wiring issue.
Oh yeah I forgot to add that part. I tested all 4 just to be sure it wasn’t a bad light or a fluke somehow. The 1,2 and 4 pigtails illuminated very bright and 3 was just dead.
Also my Ecm is in the car under the radio with a kick panel on each side. VERY easy to get to
So I just need to backprobe that 104 pin?
[quote=”K5mudlife” post=66012]K then yea now you just gotta find your issue[/quote]
LOL that is my issue! I got this far on my own just need help buttoning it up.
How do I check to see if the pigtail is getting power?
How do I check if the ecm is putting out signal? Is that 104 pin power? If so what’s ground? Any common ground?
sorry first time actually having to diagnose a fuel injection problem.
K do this compare 3 to the other fuel injectors, look to see if they have the same color wires and if you wanted to check for power just hook your meters black lead to ground and use the red lead on the back probe pin. for somereason that diagram doent show wire colorsbut yes if you were gonna back probe the pcm it would be with your red lead hooked to positive and your black lead hooked to your back probe pin and with the vehicle running you should pulse a ground and you do this with your meter set to dc volts. And pin104 is correct. By the way if you need so,e back probe pins i just go to walmart and pick up a box a t pins they are very inexpensive and work great.
By looking at the print. Your 12v comes from the
ignition switch and goes to the injectors. Disconnect
injector 3. With key on engine off see if 12v is read
to ground.If read then ohm the ground 104 back to the ecm.By all means, go ahead and perform your tests to be sure but i have had several Nissans with failed injector drivers in the PCM.
You can send it for repair and might already be programed when returned if you supply the rebuilder with the correct info.
Ok so if it is the PCM what are my options there? Just replacement? Should I go ahead and pick up another one? A quick google search just brings up “nissan altima ECM ECU PCM computer” So I’m assuming it’s all the same unit that I’m talking about.
I don’t really have the $$$ to buy a new one, would one from a salvage yard be fine for a while? IF I did get one from a yard can I just plug it in or does it need to be reprogrammed?
Thanks for your help!
As mentioned previously, complete your tests before condemning the computer. If needed a used one should be fine but it might need to be programmed. You would have to try it. Be prepared to have it delivered to a Nissan dealer for that, if needed.
Eric uses a rebuilder for some of his electronics and is another option. He says he’s had good luck with them. The link to their website is here. If you contact them i’m sure they would have all of the info you need.
Today I checked for power at the connector and it was there. Ground was not, I then back probed my ecu to make sure it was pulsing when I tried to start the car. It was. Then I moved on to continuity test, the injector ground at the ECU did not have continuity with the ground pin on the connector so the hunt began.
I checked all around the ECU and those were fine. Then I took off the harness that holds the injector and probed the wire about midway and hazaa continuity! I probed until I didn’t have any and there was a mysterious bundle of tape that looked like the other tape on the other connectors… it was not lol
I patched it really good with some tough wire that I had that was the exact same gauge. Only 1 1/2″ or so. Put it all back together and it runs fantastic!!
Thanks for all the tips!
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