Identify
OBD-II P0 code lookup
Generic SAE J2012-style P0 meanings for the codes workshops search most. Manufacturer-enhanced codes and confirmed-fix trees belong to Identifix, AllData, and ProDemand — we do not rebuild them.
P0420
- Family
- Powertrain (engine / transmission)
- Kind
- Generic SAE (second character 0)
- Subsystem
- Auxiliary emission controls
Common SAE meaning: Catalyst system efficiency below threshold (bank 1)
- Exhaust leak before rear O2
- ageing cat
- upstream misfire history
Generic SAE code — meaning is public. Manufacturer-enhanced (P1/P2/P3) and confirmed-fix databases are paid products (Identifix, AllData, ProDemand).
Common P0 shortcuts
Theory
P0 is public. P1 is not.
A five-character DTC starts with the family (P powertrain, B body, C chassis, U network). The second character 0 means a generic SAE J2012 meaning; 1–3 are manufacturer-enhanced. Australian diesel shops see the same P0 lean/misfire/cat codes plus aftertreatment codes (NOx, DPF, AdBlue). A code is a test plan, not a parts list.
How to use it
- Role
- Technician (P03) during DVI / diagnosis
- Shop-day step
- DVI → ESTIMATE
- Do
- Write the code on the RO, read freeze-frame, then pick the next test (fuel trim, smoke, contribution).
- Do not
- Do not sell a catalyst from P0420 alone, or a gearbox from P0700 alone.
Official sources
Related tools
Not a diagnosis. A code is a symptom pointer. Confirmed fixes are a paid information product.