Hi, I had my 1997 Chevrolet 5 speed S-10 truck (138,000 miles) tuned 4 months ago. I kept getting P0135 code. I tuned it myself, wires, cap, rotor, plugs etc. Also installed 4 new O2 sensors. Yesterday I got the idiot light again. This time the code is P042. I checked manual and it says " Catalyst System Efficiency Below Threshold". Any suggestions on fixing this one would be appreciated. My wild guess is catalytic converter is bad??
Stop guessing and have it analyzed with an OBDII tester. There are many conditions that can cause the converter to look bad. Also if you were running it a long time with misfires the converter could have been destroyed. Check all the connectors on the O2 sensors. Check for other codes...
If P0420 is the only active code, then most likely the converter is bad. If the car was misfiring for a long time the converter may have been damaged.
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