KARVYRAMULTI-CODE CORRELATION
P0300 + P0420 together
When P0300 + P0420 appear together, diagnose the relationship between them before treating each code as a separate parts purchase. This combination points attention toward misfire plus catalyst-efficiency evidence on gasoline engines.
Why multiple codes change the diagnosis
Two or more codes can share a power feed, ground, connector, harness path, operating condition or upstream mechanical cause. KARVYRA’s hypothesis engine groups correlated evidence and asks whether one root cause can explain several codes at once.
Shared electrical pathPower, ground, reference voltage, network or harness.
Shared operating conditionLow voltage, oil pressure/flow, vacuum leak, temperature or load.
Cause and consequenceOne fault may create another monitored failure.
Independent faultsSometimes codes are unrelated; evidence must prove the link.
Next Best Test
The best next test is the one that can separate the leading explanations with the least cost, time and risk. That is more useful than replacing the component named in the first code.