About a month ago the service engine light soon light came on. It stayed on for days , then went off for a few days. This has continued for 6 weeks now, I checked the gas cap and that was fine. Was at the dealer for yet another recall(#9) and they checked it. At that time the light had gone off and they found no codes stored in the computer. The cycle of on and off continues.. Any ideas.. I'm sure other Altima owners must have the same problem

It can be very frustrating when the car won't cooperate. The tech may need to see the car while the light still on. I would suggest that next time the light comes on, drive straight to the dealer without turning the car off, and ask if someone can check the code.
Are you having any drivability symtom's? Rough running or anything else?
If it's just the light coming on, your problem may be the Exhaust Gas Recirculation Valve (EGR). It may be sticking slightly, either open or closed. Or stuck completely.
Find out that code and let us help you.

If it is a "Service Engine Soon" Light and not the "Check Engine" light then it is just to let you know that you are due for regular service. This is typical around 75,000 to 100,000 miles but will vary. The "Check Engine" light is mostly lit due to smog issues. EGR, fuel cap, o2 sensor etc. This is the one that will provide a code explaining why the light came on.

Since the introduction of OBD-II, the terms are synonymous.
The malfunction indicator lamp (MIL) is the same as the Check Engine lamp is the same as the Service Engine Soon (SES) lamp.
The OEM does not provide a Maintenance Required Indicator for this model.

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Originally Posted by noluckwithcars

service engine light
Did like you said. Drove to an Autozone when the light was on and
the code was U1000 and U1001. Found it on a Nissan Help site.
Said it is the "can comm circuit". The computer module is not communicating with a component. Would this be easy to check?
Still no drivability issues. They cleared the code and it stayed off for a day, then came back on.

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Those codes indicate a problem with communication (CAN = Controller Area Network) between the Engine Control Module (ECM) and the Transmission Control Module (TCM). Possible causes: an open or short within that harness or poor connection at the connector(s).

Attachment 6835

Is the vehicle shifting properly?
You may be well served to take this concern to Nissan or other qualified repair facility.
Testing continuity is very specialized with circuits like this and requires some finesse.

The light can continue to come on even after a complete servicing. This is because of some other issue which in some cases will store a code, and in some cases will not.

Quote:

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Originally Posted by CaptainRich

Those codes indicate a problem with communication (CAN = Controller Area Network) between the Engine Control Module (ECM) and the Transmission Control Module (TCM). Possible causes: an open or short within that harness or poor connection at the connector(s).

Attachment 6835

Is the vehicle shifting properly?
You may be well served to take this concern to Nissan or other qualified repair facility.
Testing continuity is very specialized with circuits like this and requires some finesse.

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Captain Richs' answer makes sense. I have noticed that my transmission indicator lights have
Gotten weird. They blink and sometimes they go out. I also just noticed that when I shift from
DRIVE to 3 , sometimes nothing happens. Other times it works like it should so I think his
Answer is dead on. It took a while to notice since I hardly ever use "3".