Hi guys, new to the forum. I purchased an 03 Supercharged S2000 about a month and half ago and my Emissions test notification came in.

I de-tuned the car (Map sensor, Injectors, Spark Plugs, Belt off Super Charger, Stock ECU installed, CAT installed) and I got 2 CELs.

The first code i got was P0411 - Secondary Air Injection Incorrect Upstream Flow Detected but we seemed to have fixed that issue.

The second code I had is P0132 O2 Circuit High Voltage (Bank 1, Sensor 1) which later changed to P0131 O2 Circuit Low Voltage (Bank 1, Sensor 1) so my thought was that it was a bad O2 sensor so we swapped in a brand new primary sensor. We cleared the code, started the car up and it idled strangely for about 2-3 min and then as soon as the CEL came on the idle returned to Normal.

Plugged in the OBD2 reader and the code displayed P0131 O2 Circuit Low Voltage (Bank 1, Sensor 1) again...

My friend and I are at a loss here, the car drives fine, doesn't idle rough, doesn't die at high rpms, its just that stupid CEL that wont go away. Any thoughts on what it could be?

 

Why did you opt to de-tune the car?

 

I was told by the previous owner that I would have to swap these parts in order for the car to pass emissions. I was also told the Engine management system does not communicate with the OBD2 and with all of the parts on it there was no way it would pass.

 

bump

 

Ah I see. Somewhere along the de-tune something happened to throw that CEL. It could have been there prior to the initial install and tuning of the EMS but reappeared with the stock ECU back in charge. Have you carefully checked all the connections to and from the ECU? That low voltage error could indicate a bad connection or even a sensor somewhere along the line.

 

The ECU swap was plug and play so all of the plugs went to all available slots in the ECU except the far right one which doesn't have any pins in it anyway. The only plug that was left over from the standalone to stock ECU was one for the installed wide band gauge.

 

In case anyone stumbles upon this post, I got my issues resolved.

The P0411 code was due to the secondary air pump malfunctioning. Replacing this resolved that CEL (apparently this a known issue from Honda)

The P0131 / P0132 was due to the shop that tuned the car. They had apparently cut one the primary 02 sensors cables going going into the ECU and spliced it into the wide band. This was all done by the previous owner so i had no knowledge of this.

Hopefully this helps someone if they come across this, at least for the P0411 code....