P0135 O2 Sensor Heater Circuit Malfunction Bank 1 Sensor 1

P0135 points to a heater-circuit malfunction for bank 1 sensor 1. The heater helps the upstream oxygen or air-fuel sensor reach operating temperature quickly.

Code status

Needs verification

Not yet verified against SAE J2012_202509 / J2012DA. Treat unverified rows as a lookup aid, not repair authority.

System
Fuel / Air
Scope
iso-sae-controlled-p0
Standard
SAE J2012 / ISO 15031-6
Source
legacy-import

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not confuse a heater-circuit code with a mixture-reading code. The fault path starts with heater power, control, and wiring.

Useful checks before replacing parts

Related OBD-II codes

These nearby fuel / air entries can help compare wording and fault area. They may share the same verification status as the source database.