I have 1997 Chevrolet pickup 1/2 ton, V6, 4.3 L with 130,000 mile. It running rough, engine lit on, with scan code:
P0300 Random/multiple cylinder misfire detected
P0340 Camshaft position sensor circuit Malfunction
P0135 O2 Sensor heater circuit malfunction (bank 1 sensor 1)
I replaced: Spark Plug & Plug wires, cap & rotor, electronic module (near the coil), Camshaft position sensor and Crankshaft position sensor. It still have the same problem. Please help.

 

You could try tapping on your catalytic converter and see if you here a rattle if you doo it could be plugged and that would through the O2 sensor off. Im not sure about the Camshaft position snesor. Try clearing your codes then reading them again to see if they were cleared.

 

i agree, you need to make sure the codes that come back (if any) are the same ones

 

at 130k its a sure thing the injectors and poppets need to be replaced, the fuel pressure should be checked also, and the o2 sensors are probably pretty worn as well

 

Hi Suzuki-guy,
The catalytic converter did rattle and I did have it replace, actually the code: “P0135” only come up after I replace the converter. That makes me more confuse?<O</O

 

Did you replace your O2 sensors too? You may have a malfunctioning O2 sensor.

 

95% of the time 02 heater circuit code are bad O2 sensors.However I had a 1998 grand am Wednesday that failed OBDII emission for a O2 heater code and a evap code and the actual problem was in the under hood fuse box. The ERLS fuse ( or something like that) was not getting full power though the box which was the power source for the O2 heaters and evap system

 

I just clear the scan code and re-scan it, now I stil have code: P0135 and P0302 (cyl # 2 missfire) but at least I clear P0300 and P0340. Not sure how P0135 and P0302 related?

 

Today I change O2 sensor, clear the code, now the engine light is off and only code I have is P0302, still running rough?

 

Did you replace all the 02 sensors or just one?