DO NOT REPLACE YET
A heater code is not an O2-sensor verdict
The heater exists to bring the sensor active quickly. A heater-performance fault can involve the sensor heater, its feed/control path, connectors or wiring.
LS1 · 2000 · HO2S HEATER
2000 LS1 P0135 / P0155 Front O2 Heater Diagnosis
Front oxygen-sensor heater faults need heater-system diagnosis, not automatic oxygen-sensor replacement.
APPLICATION: 1998–2002 Firebird / Formula / Trans Am 5.7L LS1 only where the page states the exact year. Exact-year service strategy controls.
Application
This page is for the 2000 5.7L LS1 front sensors: Bank 1 Sensor 1 / P0135 and Bank 2 Sensor 1 / P0155. Do not borrow V6 or later-year circuit details.
OBSERVE → MEASURE → ISOLATE → PROVE → REPAIR → VERIFY
- Save all codes and cold-start failure data.
- Check whether one bank or both front heaters are affected; multiple simultaneous heater faults raise the priority of shared power/protection/harness checks.
- Inspect header/exhaust-area wiring for heat damage, stretching and connector problems.
- Use the exact 2000 LS1 schematic/procedure to prove heater feed and control before condemning the sensor.
- Repair the failed circuit/component.
- Verify from an appropriate cold start because the heater monitor is temperature/state dependent.
Long-tube checkpoint
If the fault appeared after header installation, inspect routing, extensions and heat exposure first. Do not convert installation timing into proof that both sensors failed.
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 →