1999 Chevrolet Corvette P0137 and P0157 - Emissions Test Failure Diagnosis
My girlfriend recently had her 1999 Chevrolet Corvette tested for emissions, and it failed due to O2 sensor fault codes P0137 and P0157 — indicating low voltage in the downstream oxygen sensors for Bank 1 and Bank 2. The vehicle has approximately 80,000 miles on it and is otherwise bone-stock, with only a Borla cat-back exhaust installed when new. There are no drivability issues — the car runs smoothly and performs as expected. Based on common forum discussions, it appears likely that the downstream oxygen sensors have degraded or failed. Is this a reasonable assumption? I'm concerned about spending over $200 if this is not actually the root cause. I can clear the codes manually, but I don't own a specialized scan tool and am wary of being misled by dealership technicians. What are the most cost-effective troubleshooting steps to take before replacing sensors? Any guidance on verifying sensor health or checking for underlying electrical issues would be greatly appreciated. Thanks, Ed
If you're looking to clear the codes, visit Auto Zone — staff won't do it for you, but they'll provide a free scanner so you can clear them yourself. They also offer free code reading and diagnostics. Start by checking the wiring harness and connections for any visible issues such as loose fittings, corrosion, or dirt buildup that could interfere with signal transmission. If all physical connections appear intact, then the downstream O2 sensors are likely the culprit. Just remember — these sensors can be expensive to replace!