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2003 Chevrolet Express 6.0 Engine Fault Codes P0154, P0174, P0300: Causes, Diagnosis & Fixes

Model: 2003 Chevrolet Express Fault Code: P0154 Posted: 2010-02-22 10:01

I own a 2003 Chevrolet Express 6.0 with 92,000 miles. The engine malfunction light flashes only when driving over 60 mph and stops when I slow down. My OBD-II scanner shows three fault codes: P0154, P0174, and P0300. I have not yet performed any repairs or diagnostics. Are these codes related? What does 'Bank 2 Sensor 1' mean? I'm looking for clear guidance on what to check first—such as cleaning, replacing components, or addressing underlying issues—and what steps to take if those don't resolve the problem. Any advice would be greatly appreciated.

Related fault codes

P0154P0174P0300

Comments (5)

Anonymous 2010-02-22 11:47

It's likely that the catalytic converter on Bank 2 (passenger side) is clogged. This can cause performance issues and trigger multiple engine codes.

Anonymous 2010-03-16 21:34

Yes, these codes are interconnected. 'Bank 2 Sensor 1' refers to the upstream oxygen sensor located between the exhaust manifold and the catalytic converter on the passenger side of the engine. Bank 2 means the side without cylinder #1 (like a Ford V8 configuration). The P0174 code indicates the system is running lean on that bank—likely due to low fuel pressure or a vacuum leak. The presence of P0300 suggests a misfire, which may stem from an intake gasket leak on the passenger side. I've seen this issue frequently and recommend checking for vacuum leaks first. No strong smell or power loss typically indicates a clogged converter is less likely.

Anonymous 2010-03-17 06:49

Apologies, but Sensor 1 is actually the upstream oxygen sensor—located between the exhaust manifold and the catalytic converter. Bank 2 refers to the side of the engine that does not contain cylinder #1 (as in a V8 configuration). While I agree with checking for vacuum leaks and fuel pressure, it's important to clarify that the O2 sensor location is upstream, not downstream.

Anonymous 2010-03-22 16:29

Thanks for the clarification. The van still has normal acceleration and no smell from the catalytic converter—so a plugged converter seems unlikely. How should I go about testing for vacuum leaks? Is there an easy method (like spraying brake or carb cleaner) to detect them without removing intake components? Should I consider replacing the upstream O2 sensor on the passenger side? And if so, what are the chances that this is actually the root cause? Thanks again—your insights are very helpful.

Anonymous 2010-03-22 19:45

A smell is not a reliable indicator of a clogged catalytic converter—I've seen many converters with no odor and others with strong smells despite being fine. To check for vacuum leaks, spray brake or carb cleaner around intake gaskets and hoses—any momentary improvement in the engine light behavior indicates a leak. Replacing an O2 sensor can be tried, but on GM trucks, especially older models, many new sensors come with faulty converters or are not the actual root cause. Misfires from low fuel pressure, vacuum leaks, or poor fuel delivery can also generate P0154, P0174, and P0300 simultaneously. A clogged converter may contribute to misfires but is not always the primary issue.