CEL On Nissan 240sx OBD1 1995

[ruah_23]

I had CEL on on my OBD1 nissan. It reads code 34 and 105. I reset the code without fixing the problem which is knock sensor and egr valve. The CEL didn't turn back on. Is the sensor just reading wrong or should I replaced the parts that cause the light to came on?

Help pls before I order the parts.

[green91]

It will sometimes take 2 solid drive cycles for the codes to come back on. Maybe longer if they are intermittent codes. obd1 ecu are dumb, usually the only time they set a code is if there is an open in the circuit or the resistance wrong.. check your grounds and stuff just in case.

[ruah_23]

What do you mean by 2 solid drive cycles? Like crank the car and drive it twice?

Update: i drove it a bunch and no cel. But i replaced the o2 sensor just now and the light came on. The code wasnt for the o2 sensor but i replaced it anyway since it's over 100k miles.

Do i have to reaet the ecu everytime i replaced a sensor? Gonna pull up the codes again later to see whether it's the same on.

[green91]

yeah some ecu require the vehicle to go through 2 drive cycles to set a code.. usually a short drive.

theres no point in replacing an o2 due to mileage unless youve got a running issue.

you shouldnt have to reset the ecu over a replaced sensor unless it was causing a CEL

[ruah_23]

Awesome! Thanks man!
So if i check the sensor, and it's good, does that mean that my engine is knocking? It drives fine..

[green91]

No it means you need to check the wiring from the sensor to the ECM.

[ruah_23]

Gotcha. Will do it and give updates.