ECU reset - RPM isn't changing during the "test"

[haveblue]

Posted in General Discussion but didn't get any responses...so here goes:

My CEL recently started showing code 42. It's the first time I've ran into a code and the first time I've tried an ECU restart:

http://itisfresh.com/how-to-reset-ecu-acura-nsx.html

I turned the car off, pulled the fuse for 15mins, put the fuse back in, and started the car. I let it idle for 10mins and the RPMs never changed. The car just idled the entire time.

The CEL still remains on after I started the car again, but I'm not sure if the ECU actually reset since it didn't change RPM during the test.

 

[pgilliam1]

Code 42 is for rear bank O2 sensor. Check the wiring to the sensor (sometimes it melts onto the exhaust).
Is the engine running oddly?

 

[EdinKali]

I believe that code is for rear 02 sensor heater. Time to change that O2 sensor if you haven't done so already. Resetting the ECU isn't going to fix that. I am guessing the idle didn't change(idle calibration procedure) due to the thrown code. I would surmise that the car isn't going into closed loop mode with a code being set.

 

[haveblue]

I'll check the wiring. Engine is running perfectly fine. Feels and sounds normal.

 

[pgilliam1]

I'm going to assume you did the ECU reset with a warm engine. When the engine is cold it runs in open-loop mode and does not use the O2 sensors. After the engine warms up it runs in closed-loop mode and uses the O2 sensors to trim fuel levels. You could pull the clock fuse with the engine cold and that should erase the O2 fail code from the ECU (just don't turn the ignition back on immediately after shut down and it won't store the cold settings). The failure code should not return until the engine warms up and the ECU recognizes the O2 sensor. It may have been just a glitch and won't return. Usually a bad O2 sensor causes running problems but I guess maybe not always. Good Luck!

 

[Daedalus]

O2 sensor heater won't change how the car runs. It just means it'll take longer for the sensor to heat up to get the ECU to closed loop. Nothing that needs to be fixed right away, but I would fix it so the CEL doesn't mask any other issues that might come up.

 

[pgilliam1]

O2 sensor heater won't change how the car runs. It just means it'll take longer for the sensor to heat up to get the ECU to closed loop. Nothing that needs to be fixed right away, but I would fix it so the CEL doesn't mask any other issues that might come up.

I guess I need a course on O2 sensors. From the above posts it seems the O2 sensors have a heating circuit built into them along with the O2 sensor. I thought the exhaust heated the O2 sensor to bring the ECU into closed-loop. As R. Perry would say, "OOPS".

 

[Daedalus]

Yup, 2 separate circuits. Some cars, mostly older, have unheated sensors. They spend more time in open loop and thus use more fuel overall (hence the emissions-required CEL for bad heaters). Not much of an difference for long open road drives, but short drives and stop-and-go it can make a measurable difference. I had a scanner on an old Bronco once and you really had to keep the throttle on it to keep it in closed loop.

 

[pgilliam1]

Yup, 2 separate circuits. Some cars, mostly older, have unheated sensors. They spend more time in open loop and thus use more fuel overall (hence the emissions-required CEL for bad heaters). Not much of an difference for long open road drives, but short drives and stop-and-go it can make a measurable difference. I had a scanner on an old Bronco once and you really had to keep the throttle on it to keep it in closed loop.

Thanks for curing a small part of my seemingly never ending lack of knowledge. So much to learn, so little time.