LS1 · 2002 · P0158
2002 LS1 P0158 HO2S High-Signal Diagnosis
2002 LS1 P0158 diagnosis that separates a rich-running engine, signal-circuit fault and sensor/connector problem before replacing the oxygen sensor.
APPLICATION: 2002 Firebird / Formula / Trans Am 5.7L LS1. This page is specific to the P0158 strategy.
WHAT THE CODE MEANS
High sensor signal is not automatically a bad sensor.
The PCM supplies an HO2S bias near 450 mV and monitors sensor voltage. For P0158 it is looking for a signal that remains abnormally high under the applicable test conditions.
DO NOT REPLACE YET
Before replacing the HO2S, separate a signal circuit held high from an engine that is actually rich.
CHECK THESE BRANCHES
- Connector water intrusion that can allow heater B+ to bleed into the signal circuit.
- Fuel pressure too high.
- Rich or leaking injectors.
- Fuel-saturated EVAP canister/purge fault.
- MAF installation and direction. A backwards MAF can drive the system rich.
- HO2S wiring contamination/damage.
- Intermittent throttle-position information that falsely indicates acceleration.
LONG-TUBE / MODIFIED EXHAUST
Document sensor location, extension harnesses, exhaust leaks, catalyst configuration and calibration before treating a modified exhaust exactly like the stock system.
AFTER THE FAILURE IS PROVEN
Use the proven failed branch—not the original symptom—to choose the replacement. Go from diagnosis to the Parts Verdict →