Generic OBD DTC
Ford P0420: Catalyst System Efficiency Below Threshold (Bank 1)
The PCM has determined catalyst efficiency is below the OBD threshold for bank 1 — a different finding from P1000 readiness status.
What the code tells you
- Catalyst monitoring detected efficiency below the calibrated threshold on bank 1.
What it does not tell you
- That P1000 “means” a bad converter.
- The root cause without diagnosis (exhaust leaks, sensors, converter, fuel control, etc.).
Diagnostic direction
- 1
Do not treat P1000 and P0420 as the same code.
- 2
If both are present, P0420 is the efficiency finding; P1000 may still reflect incomplete monitors after a reset or alongside another incomplete test.
- 3
Follow Ford-guided catalyst diagnosis rather than replacing parts from P1000 alone.
Related codes
P1000, P0430
Possible causes are listed only when they are this code’s actual meaning — not a generic template pasted onto every DTC.
This site provides general diagnostic information. Vehicle procedures vary by model, year, engine, and calibration. Follow Ford service information and local regulations, and use a qualified technician when diagnosis or repair exceeds your experience.