OMG its Jason

While sitting at a light today, my engine light came on. After reading the code, this is what came up "P0420 TWC System Low Efficiency Bank 1"
Anyone have any reason for this?
Car has heads/cam/headers with no cats but I believe it was tuned.
As always, thanks in advance.

ArKay99

That's for the Catalyst system. It's a DTC just as you described, but I don't know about the TWC. The PCM is trying to tell you that your driver's side cat isn't working too well. Since you don't have cats that would be the explaination but if it's been tuned the DTC should be set to not report. Usually the text right after the DTC code is 'H', 'C', or both 'HC'. Not sure what TWC means. You might need to have it re-tuned.

luch90

twc stands for three way converter. the tuner should have changed p0420 and p0430 to no error reported to avoid this. how long did it take after the headers/no cat setup was installed before the light came on? newer model years seem to be more stringent on how well the converter works. some older cars will only sporadically detect low efficiency when there are no cats present. ive seen c6's with headers/high flow cats set these codes commonly

OMG its Jason

I just bought this car a couple weeks ago and have put about 500 miles on it. "from 11,800 to about 12,300" It just came on this morning.
The only DTC's that showed up "H and C" were P0420 and then the 4 TPS "I have aftermarket wheels with no TPS installed". There were other codes listed but they were all listed under "H"

npm

the only reason you are getting this is the tuner didn't tune it out.

trussme

Your "Tuner" needs to either tune these codes out OR install "02 simulators". Headers (& no cats) will cause these codes.