Check engine light goes on and off

[kwbboyer]

Hi my name is Kevin and I have a problem with my 1994 pathfinder that stumps everyone. The check engine light goes on and off at will. When it is on it seems to run a little ruff but will quickly go ff when I hit the highway. When i slow down on thee off ramp it goes back on. few blocks further goes away. The whole problem was seemingly gone for two months back back again??? any suggestions?

[MinisterofDOOM]

If you can give us the code that's showing, it'll help narrow it down. It could be something like knock or oxygen sensors, but without a code we'd be sending you on a wild parts chase.

Even if the light goes off, it should still store the code as "pending" for a few dozen miles, so it can be read even after the light goes back off.

[kwbboyer]

cant find anyone with ob1 reader. so im not sure of code. changing o2 sensor when it comes in tomorrow. Thanks

[MinisterofDOOM]

Let us know if that fixes it. If not, my second guess would be knock sensor. It's a pretty common cause of check engine lights with the VG. It happens to my '97 occasionally, but only under very specific circumstances (and, like yours, it's usually under NON-stressful conditions like coasting). It always clears itself, but the time it takes to clear seems pretty random. Knock sensor probably is actually going bad, but until it becomes a more frequent issue I'm happily ignoring it.

As for the OBD reader, any auto parts chain stores should have one they'll let you use in the parking lot. Cheap ones are pretty decent these days, too. I keep one of these in each of my OBDII-equipped cars because they're so cheap. It even includes some of the more common code definitions, but it doesn't play nice with ALL cars (some 90s Chryslers have really slow computers that take too long to respond, for instance).
https://www.amazon.com/gp/product/B007X ... =UTF8&th=1
(I've got the $35 version, not the $110 version)

[Rogue One]

I've moved this to the Pathfinder forum to get responses from the members that are most familiar with your vehicle.

There are some codes that issue an error, but the error may not repeat. One common one is the fuel filler cap. The engine goes through a periodic procedure where it is sensing the pressure in the fuel system to determine if it needs to purge the emission canister. If the pressure isn’t correct, an error is thrown. This process doesn’t happen every time you drive the car; it happens when the computer determines it’s necessary. Well, if the gas cap isn’t set and sealed properly when the test takes place, an error is thrown. If the cap is removed and put back on correctly, the next time the test runs, the pressure is correct and the engine light goes out.

Even if the gas cap is seated correctly, it may be damaged/defective, so replacing it might solve the problem.

[Frank01pathfinder]

My engine light went off and on a few times on my 01 pathfinder. Never thought it would be this easy but a new gas cap has fixed it for now. Its been off for a few months hoping it stays this way.