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2003 Chevy Silverado P0157 O2 Sensor Low Voltage (Bank 2 Sensor 2) & Evaporative System Not Ready - Diagnosis and Next Steps

Model: 03 Silverado Fault Code: P0157 Posted: 2015-06-08 13:23

I own a 2003 Chevrolet Silverado LT 1500 V6 Extended Cab with 178,000 miles. I'm currently experiencing two diagnostic trouble codes: P0157 (Oxygen Sensor Circuit Low Voltage - Bank 2 Sensor 2) and Evaporative Emission System Not Ready. I've already replaced the gas cap and the passenger-side oxygen sensor located behind the catalytic converter. After performing the manufacturer-recommended test drive, I successfully achieved catalytic converter readiness during a trip to a destination, but experienced a cylinder 6 misfire on the return journey. I reset the codes and replaced the plug wires (which were only one year old), eliminating the misfire. Despite these efforts, the P0157 code has returned and remains persistent. The Evaporative System has never reached 'Ready' status. While I haven't yet performed a thorough inspection for vacuum or exhaust leaks at engine or header connections, I suspect they may be contributing to the issue. I understand from technical sources that P0157 is typically not related to catalytic converter performance—but with this code persisting and evaporation system readiness failing, I'm concerned about passing emissions inspections. The truck currently shows no dashboard warning lights. What should my next diagnostic step be? Should I consider replacing the exhaust manifold or headers? Or is there a more targeted approach using fuel pressure testing, oxygen sensor signal voltage checks, or leak detection? Thanks for any guidance! Brad

Related fault codes
P0157
Comments (5)
Anonymous 2015-06-09 09:11

What are the current diagnostic codes? Is your vehicle stock configuration? Do you have access to an OBD-II scanner with live data readings (such as real-time sensor voltages and operating temperatures)? Note: Erasing a code clears stored history and resets all monitors, including the evaporative system and catalytic converter readiness — this may explain why the evap system remains not ready after reset.

Anonymous 2015-06-09 12:41

Current codes: I've erased them (no active codes currently). Vehicle is stock with no modifications. I use an Actron CP9550 OBD-II scanner, which reads stored codes and monitors like catalytic converter readiness, evaporation system status, oxygen sensor readiness — but it does not provide live data such as real-time voltage or temperature readings. I learned that resetting the misfire code caused the catalytic converter to go back to 'not ready' — a key point about monitor resets. I'm now trying to determine what steps are next to resolve both P0157 and Evap System Not Ready. Any advice would be appreciated! Brad

Anonymous 2015-06-09 14:22

You're currently showing no active issues — but the presence of a persistent code indicates an underlying problem. Monitor operation is key: drive under normal conditions and observe if any codes reappear. A basic OBD-II scanner would be ideal to check live data, such as oxygen sensor voltage signals. If available, using a digital multimeter (DVOM) to probe the actual signal wire from Bank 2 Sensor 2 could help verify whether the sensor is producing a valid signal or if it's stuck low. Note: You currently have a code reader — not a full diagnostic scanner with live data capabilities.

Anonymous 2015-06-10 13:00

What I've already replaced: - Passenger-side O2 sensor behind catalytic converter - Gas cap - Plug wires (only one year old) I need to pass an emissions inspection, and with both the P0157 code and Evaporative System Not Ready, the truck will fail. Last night I drove around the city in stop-and-go traffic. Upon returning home, here are the readings: - P0157: O2 Sensor Circuit Low Voltage (Bank 2 Sensor 2) - Emissions Monitors: - HTD O2 Sensor Ready - Oxygen Sensor Ready - Evaporative System: Not Ready - Catalytic Converter: Ready - Comprehensive Component: Ready - Fuel System: Ready - Misfire: Ready No dashboard warning lights are present. Will this truck pass an emissions inspection with the P0157 code active? Any insight would be greatly appreciated! Brad

Anonymous 2015-06-11 15:16

The Powertrain Control Module (PCM) detects a problem — you need to identify exactly what that issue is. According to technical specifications, P0157 triggers when the oxygen sensor signal voltage remains below a threshold for an extended period: Option 1: The HO2S signal stays below 90 mV for 80 seconds. Option 2: During Power Enrichment mode, the signal remains below 420 mV (or ~5.0 V) for 5 seconds. Without a scanner to monitor live sensor voltage, diagnosing this is difficult. Consider checking fuel pressure — low pressure can cause lean conditions. Possible root causes: - Lean injector(s): Perform an injector balance test. - Fuel contamination: Water near the in-tank fuel pump may cause a lean exhaust condition. - Exhaust leaks: A leak near Bank 2 Sensor 2 (typically downstream of cylinder 6) could interfere with sensor readings. - Vacuum or crankcase leaks: These can also create a lean condition. If all these factors are ruled out, the issue may lie with the O2 sensor itself — especially given its age and location. OEM-quality sensors are recommended for reliable performance in older vehicles like this Silverado.