Hello guys, greetings from Belgium.

After years of reading, this is my first post here. I have an issue with my second S2000. The car is refused at the anual technical control. They check the CO2 emissions in Belgium, and my car is far from being within tolerances ranges.

There are the symptoms :
- CEL P0135 (Primary Heated Oxygen Sensor (Primary HO2S) (Sensor 1) Heater Circuit Malfunction). I have tested 6 used O2 sensors and 1 new O2 sensor + ECU reset. CEL still there, same code.
- Too much CO2 (according to the technical control crew, the value at idle should be "0.30", and the car seems to reject around "2.0").
- According to the test machine, the car runs too rich aswell.
- Sames results with highflow or OEM catalytic converter.

The car runs very well, perfect revving, VTEC triggers perfectly, no hesitation at all. No CEL error code about the AFR.

My thoughts : About the CEL, I suppose that the cable between the ECU and the O2 sensor or the ECU itself are in fault. But since the CEL code indicates the heater circuit of the O2 sensor, I suppose that once O2 sensor is at the right temperature, the AFR should not be impacted by this O2 sensor. So the O2 sensor is maybe not linked to the O2 overhall issue, IDK.

Any idea?

Sorry about my english, and thanks in advance ! :-)

EDIT FIXED : Issue fixed. The ECU was faulty and switched to safe mode, wich consist of low down the AFR (conservative behavior, If you run rich you are not running lean). So, running richer = more CO2

The replacement of the ECU fixed the CO2 issue and the CEL.

 

Which brand sensor? Fuel trims? Valve adjustment done when?

 

OEM sensors.
By fuel trim, you mean AFR in the map ? The ECU is the OEM one, so the car should not be mapped. (The car is an AP1, gonna edit the thread)
Last ​​​​​​valves adjustment was 3 years and less than 6k miles ago.

 

Oe ecu adjusts fuel trims to a degree. Check wiring and connections too for cracking/poor continuity

 

Issue fixed. The ECU was faulty and switched to safe mode, wich consist of low down the AFR (conservative behavior, If you run rich you are not running lean). So, running richer = more CO2

The replacement of the ECU fixed the CO2 issue and the CEL.

Thanks.

 

I'm not from Belgium but I'm pretty sure they are measuring CO (Carbon monoxide) and not CO2, just to clear any misunderstandings in the future.
High CO is a byproduct of incomplete combustion, in this case from to much fuel added by the ecu.

 

Thanks for letting us know the end result!