O2 Oxygen Sensor Upstream Downstream for Chevrolet Blazer (1996-2001) 4.3L

Direct-Fit Upstream & Downstream O2 Oxygen Sensor Kit for 1996-2001 Chevrolet Blazer (GMT330)

What it Does: This matched 3-piece upstream and downstream oxygen sensor kit restores closed-loop air-fuel ratio monitoring and catalytic converter efficiency checks on the 1996-2001 Chevrolet Blazer GMT330 powered by the L35 4.3L Vortec V6.

The Stock Chevrolet Blazer Sensor Degradation

Factory oxygen sensors on the GMT330 Blazer with the L35 4.3L Vortec V6 endure constant thermal cycling and exhaust soot contamination. Over time, silica poisoning, trace coolant exposure, or oil ash foul the zirconia sensing element, slowing voltage switching between rich and lean states. Simultaneously, the internal heating element degrades, delaying closed-loop operation and forcing the PCM to run an overly rich base fuel map. This sensor sluggishness commonly triggers P0133, P0134, P0140, or P0171/P0174 fuel trim fault codes.

Common Symptoms of a Failing OEM Oxygen Sensor

• Check Engine Light / DTCs: Slow response or heater circuit faults like P0133, P0135, and P0141 illuminate the MIL when voltage transitions fall out of spec.
• Rich Exhaust & Rough Idle: Biased lean readings cause the PCM to command excess fuel, resulting in raw fuel odor, fouled spark plugs, and unstable idle.
• Dropped MPG & Failed Emissions: Prolonged open-loop fueling cuts highway fuel economy and increases hydrocarbon and CO tailpipe output.

The Direct-Fit 4-Wire Heated Zirconia Solution

This matched kit replaces both pre-cat bank sensors and the post-cat monitor simultaneously using OEM-spec 4-wire heated zirconia elements. Each sensor features a laser-welded stainless steel body and porous PTFE protection shield to resist thermal shock, moisture intrusion, and exhaust contamination. Factory-matched pigtail lengths and keyed weatherproof connectors eliminate wire splicing or circuit resistance mismatches. By restoring rapid 0.1V-to-0.9V switching across all three bungs, the L35 4.3L Vortec V6 PCM maintains crisp stoichiometric fuel control.

What's Included

• 2 Upstream Oxygen Sensors
• 1 Downstream Oxygen Sensor

Technical Specifications

Compatibility

• 1996-2001 Chevrolet Blazer 4.3L

Frequently Asked Questions & Fitment Warnings

Does this fit the GMT330 Blazer?

Yes. This is a direct fit for the 1996-2001 Chevrolet Blazer equipped with the L35 4.3L Vortec V6 engine. Verify your engine displacement and 3-sensor exhaust configuration before ordering, as alternate 4-sensor layouts differ.

Will this clear P0133, P0135, or P0141 codes?

Yes. Replacing both upstream sensors and the downstream monitor resolves heater circuit faults and sluggish voltage switching that trigger P0133, P0135, P0140, and P0141. Clear stored DTCs and inspect exhaust manifolds for leaks prior to road testing.

Are splicing tools required for installation?

No splicing is required. All three sensors use factory-terminated OEM connectors for plug-and-play installation into the GMT330 harness. Use an oxygen sensor socket and ensure threads are clean before torquing to factory specification.

The Chevrolet Heavy-Duty Standard

Built for the thermal demands of daily driving, towing, and off-road duty in the GMT330 platform, this matched sensor set restores factory fuel trim accuracy. Expect dependable closed-loop operation, cleaner combustion, and consistent CEL-free performance.