Operation CHARM: Car repair manuals for everyone.
Home >> Honda >> 1996 >> Prelude L4-2.2L DOHC (VTEC) >> Repair and Diagnosis >> Powertrain Management >> Emission Control Systems >> Catalytic Converter >> Testing and Inspection
Manuals through 2025 now available!

Our trusted friends have launched a new website named LEMON, which has newer manuals. It also contains all the CHARM manuals.

LEMON is the spiritual successor to CHARM, I recommend you try it!

Link: lemon-manuals.la or lemon-manuals.org.ua

(Some people have issue connecting. LEMON is investigating. For now, use Firefox or change your DNS server)

Or, hide this message: temporarily or permanently

Catalytic Converter: Testing and Inspection




P0420:
The scan tool indicates Diagnostic Trouble Code (DTC) P0420: Catalyst system efficiency below threshold.

DESCRIPTION
This system evaluates the catalyst's capacity by means of the HO2S (Primary and Secondary) output during stable driving conditions. If deterioration has been detected during three consecutive driving cycles, the MIL comes on and DTC PO42O will be stored.

NOTE: If some of the DTCs listed below are stored at the same time as DTC P0420, troubleshoot those DTCs first, then troubleshoot DTC P0420.

P0137, 8: Secondary HO2S
P0141: Secondary HO2S Heater


Possible Cause
- TWC Deterioration
- Exhaust system leakage
pro multis · About Operation CHARM