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 diagnose the catalyst from P0156 alone; the downstream sensor circuit must be proven first.
Useful checks before replacing parts
- Inspect downstream bank 2 sensor wiring, connector condition, exhaust leaks near the sensor, and harness heat damage.
- Compare downstream bank 2 sensor activity with upstream sensor behavior and catalyst-monitor conditions.
- Check for related heater, catalyst efficiency, fuel-trim, or exhaust-leak faults 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.