1998 Chevy Silverado 5.7L Engine Fault Codes P0155 & P0306: Rough Idle and Cylinder 6 Misfire

Both codes occur simultaneously. Note that P0306 refers to cylinder 6 in Bank 2, which is the same bank as P0155 (Bank 2, Sensor 1 O2 heater circuit). A faulty oxygen sensor heater circuit can contribute to misfires and poor engine performance. I recommend clearing the codes and monitoring for any return of faults. If you have access to a scan tool capable of reading O2 sensor voltage, that would provide more insight. Check power and ground connections for the O2 heater circuit (D pin for power, C pin for ground). Test the resistance across the heater coil (pins C and D) — it should be within specifications. I can share a wiring diagram if needed. Also inspect cylinder 6 spark plug; use a spark tester to verify spark presence. A clogged or faulty injector or carbon buildup in the combustion chamber could also be contributing factors.

For the O2 sensor heater circuit: connect a test light to battery ground and touch it to terminal D (heater power) — the test light should illuminate. Then, connect the test light to battery positive and touch it to terminal C (heater ground) — the test light should also light. If either connection fails, there's an issue with power or ground. Additionally, measure resistance across heater terminals C and D; if it’s outside the expected range (typically 0.5–1 ohm), the heater coil is likely faulty.