P0151 O2 Sensor Fault in 2002 Chevy Astro Van AWD: Diagnosis and Repair Guide

P0151 stands for 'O2 Sensor Circuit Low Voltage (Bank 2 Sensor 1)', which refers to the first oxygen sensor located downstream of the exhaust manifold on Bank 2. Bank 2 is the side opposite cylinder #1 — typically the passenger (right) side in most vehicles. For more clarity on Bank 1 vs. Bank 2, see: https://www.obd-codes.com/faq/what-is-bank-1-vs-bank-2.php Since you have a 4.3L Vortec engine, this applies directly to your setup. First, inspect the wiring harness leading to the sensor. If it appears intact and properly connected, replace the O2 sensor. It's recommended to replace all three exhaust oxygen sensors at once for optimal performance — though not strictly necessary. Note: P0151 is very similar to P0131 (which affects Bank 1). For reference, see: https://www.obd-codes.com/p0131 Please update us on your progress!

I have a Chevy 4.3L Vortec engine. Thanks for the clarification — that helps confirm which side of the engine we're dealing with. With two manifold-mounted O2 sensors, how can I determine which one is malfunctioning? Will auto parts stores list different part numbers based on position and side (e.g., upper vs. lower, passenger vs. driver)?

I'm not sure what you mean by 'two manifold sensors'. Are you referring to oxygen sensors? I don't have experience with this engine configuration, so I may be missing something.

There are three O2 sensors in the exhaust system. The upper sensor and the one after the catalytic converter share the same part number. However, the manifold-mounted sensor (the first one downstream of the exhaust manifold) has a different part number. I now know which sensor is triggering the P0151 code — but I'm still unsure about its exact part number.

I don't have a clear understanding of what 'manifold' sensor means, though it may relate to the EGR system. The sensors with identical part numbers are typically the upstream and downstream O2 sensors (one before and one after the catalytic converter). As previously mentioned, inspect the wiring leading to the Bank 2 O2 sensor located just before the catalytic converter. If the wiring is intact, replace that sensor. You can find the correct part number at any dealership or auto parts store — simply look up the part by vehicle model and engine type.

I checked with GM Parts Direct and learned they differentiate between right (passenger) and left (driver) sides, as well as upper and lower positions. Is the passenger side of the vehicle considered the right side? Thanks for confirming!

Yes, Bank 2 corresponds to the passenger (right) side of the engine in this configuration.

I replaced the O2 sensor on the Bank 2 side, but now I'm receiving a P1345 code — which points to a crankshaft position sensor issue. I cleaned the sensor, but the engine still runs roughly and misfires intermittently. Since it doesn't happen every time, I don’t believe it's a timing chain problem. Any suggestions on how to troubleshoot this further or whether there could be an electrical or sensor-related cause behind the intermittent misfire?