2002 Chevy Blazer LS P0135 O2 Sensor Fault - Aftermarket Sensor & Wiring Issue
I'm experiencing a recurring P0135 trouble code on my 2002 Chevrolet Blazer LS 4x4. I previously replaced both pre-catalyst oxygen sensors (B1S1 and B2S1), but the issue returned after driving a few miles. A mechanic inspected the vehicle and found a bent prong in one of the sensor plugs, which he repaired—afterward, readings appeared normal. However, today when I tried to start the car after it had been sitting all night, the 'Service Engine Soon' light illuminated before even turning the key. Upon connecting a OBD2 scanner, the P0135 code reappeared. I'm now concerned whether the replacement sensors were properly installed or if there's an underlying wiring issue. Could someone confirm: did you replace only the pre-cat oxygen sensors (B1S1/B2S1), not the post-catalyst sensor? Are there any other diagnostic codes present? Did you verify the wiring connections at both sensor locations? And were the sensors OEM or aftermarket (I used AutoZone, unsure if they are original equipment)?
Some key questions: - Did you replace only the pre-catalyst oxygen sensors (B1S1 and B2S1), not the post-cat sensor? - Are there any other diagnostic trouble codes present? - Did you confirm proper wiring connections at both sensor locations? - Were the replacement sensors OEM or aftermarket? I used an AutoZone sensor and am unsure if it's original equipment—any advice on this would be appreciated.