My girlfriend's 2000 Nissan Sentra has been getting a CEL, so I had her go up to Autozone to have them check it. They told us it was a code P0420 and P1140. I found in my Honda Civic manual that an OBDII P0420 code is a catalyst system efficiency below threshold. It didn't have the P1140 code though. Does anyone know what this is or what might be wrong with the car?

Thanks

 

what are the symptoms doc? I'm not familiar with those OBDII codes.

Just found it :
P1140 Intake Valve Timing Control Position Sensor (Left Bank) (Nis/Infiniti)

 

hehe, my WRX throws P0420 sometimes. Catalytic convertor inefficiency. Mine is because I removed one of the 3 cats in the car. If the car is unmodified, I doubt the cat would be burned up. Might just be a bad rear O2, or the car running very rich.

Intake valve sensor? Sounds like a trip to Nissan for a new one. Does that car have some sort of variable cam thing?

I'd get the valve sensor diagnosed first. It may be that its causing the P0420.

 

Anyone know where the valve sensor is located at? I don't want to have her bring the car into a dealership if it's something as easy as replacing the o2 sensor. Dealerships are always a friggin rip off.

 

Discount auto parts carry haynes manual which will tell you what those codes represent on a sentra. I had a CEL on my dad's 2000 corolla. i have replaced main 02 sensor and a full engine/fuel flush. Still problems, my next step is to get some new spark plugs and call it the day. My code was P0171 "System Too Lean (bank one)"

once you find out what those code represent, call a dealership and be nice and ask them what could be wrong. They will make you come in and pay most likely. But if you find one of the tech's in good mood he may just tell yah what it could be on the phone...

my .02

Rink

 

This is one of the few problems the QG18DE continues to show--the other is a failing MAFS.

Some info about the NVTCS (Nissan Valve Timing Control System)[for the tech guru's]:

A hydraulic mechanism in the hub of each intake cam (driven by a single-row chain) changes intake timing relative to exhaust timing. At low and moderate speeds, earlier intake valve closing improves air pumping efficiency and idle quality. At higher speeds and RPMs, later closing enhances torque output. To achieve this phase change, oil pressure moves the shaft backward along a helical gear, twisting it slightly. A solenoid operates the hydraulic control valve according to a signal from the computer, which takes airflow, rpm, coolant temperature, and throttle position into account before issuing commands. When the solenoid is energized, the cam is advanced to give 28 deg. of intake/exhaust overlap. De-energized, there's only 8 deg. The NVTCS is actually simple, and, except for the possibility of computer input problems, shouldn't cause much trouble.

But if it is diagnosed to be bad, the part is only like $52.00, so don't pay more than $100 for it to be fixed (unless you plan on doing the wrenching yourself)
Hope that helped explain where it is and what it does.
-Jordan

 

Thank you Rubberburner, that was very informative. Any idea why that might cause the secondary o2 to act up though? Or do you think they might be unrelated problems?