Circuit Description
The ECM compares the 2 waveforms of the heated oxygen sensors located before and after the catalyst to determine whether or not the catalyst performance has deteriorated.
Air-fuel ratio feedback compensation keeps the waveform of the heated oxygen sensor in front of the catalyst alternates between back and forth, from RICH to LEAN.
If the catalyst is functioning normally, the waveform of the heated oxygen sensor behind the catalyst switches back and forth between RICH and LEAN much more slowly than the waveform of the heated oxygen sensor in front of the catalyst.
When both waveforms change at a similar rate, it indicates that the catalyst performance has deteriorated.
DTC P0420
| DTC No. | DTC Detecting Condition | Trouble Area |
|---|---|---|
| P0420 | After engine and catalyst are warmed up, and while vehicle is driven within set vehicle and engine speed range, waveforms of heated oxygen sensors have same amplitude (2 trip detection logic) |
|