Emissions / AuxiliaryLow ImpactPetrol

P0421 — Diagnostic Trouble Code P0421

OBD-II diagnostic code P0421 relates to the emissions / auxiliary system. This code is logged when the ECU detects a parameter outside its expected operating range.

4+

Affected Brands

11+

ECU Platforms

2

Related Services

2

Related DTCs

Symptoms

What the driver typically experiences when P0421 is stored

!Check Engine Light
iFailed emissions test
iNo major drivability impact

Why does P0421 appear after tuning?

This code may appear after ECU modifications when the affected system monitoring has not been fully recalibrated for the new operating parameters.

How proper calibration can address P0421

WEREMAP professional calibrations include comprehensive diagnostic management for all affected systems, preventing unnecessary fault codes while maintaining safe operation.

Related Tuning Services

Relevant services for the system behind P0421

Catalyst OffDTC Off

Related Diagnostic Codes

Codes from the same diagnostic system as P0421

P0431Low Impact

Diagnostic Trouble Code P0431

P0420Moderate Impact

Catalyst System Efficiency Below Threshold (Bank 1)

Affected ECU Platforms

Denso P51J-188K6Siemens/Continental SDI3Campi LIE 2018MPC5567 CAMPI_LIEMitsubishi E6T795373 H1Mitsubishi unknownBosch MED9.1Siemens/Continental sdi3Siemens/Continental SDI4Mitsubishi MH7XXX/MH8XXXBosch me7

Commonly Affected Vehicles

MazdaMX5Denso P51J-188K6
LamborghiniAventadorCampi LIE 2018
Lamborghini6.5L_ V12MPC5567 CAMPI_LIE
MitsubishiOutlanderMitsubishi E6T795373 H1
MazdaMazda 6Mitsubishi unknown
PorscheCayenneBosch MED9.1
PorscheCaymanSiemens/Continental sdi3

Based on data from 4+ vehicle brands. P0421 is not limited to these models.

Frequently Asked Questions

What does P0421 mean?â–¼
OBD-II diagnostic code P0421 relates to the emissions / auxiliary system. This code is logged when the ECU detects a parameter outside its expected operating range.
Why does P0421 appear after ECU tuning?â–¼
This code may appear after ECU modifications when the affected system monitoring has not been fully recalibrated for the new operating parameters.
How do you prevent P0421 during remapping?â–¼
WEREMAP professional calibrations include comprehensive diagnostic management for all affected systems, preventing unnecessary fault codes while maintaining safe operation.
Which vehicles are affected by P0421?â–¼
P0421 is commonly found on Mazda, Lamborghini, Mitsubishi, Porsche vehicles equipped with Denso P51J-188K6, Siemens/Continental SDI3, Campi LIE 2018, MPC5567 CAMPI_LIE ECU platforms.
What other codes appear alongside P0421?â–¼
P0421 frequently appears together with P0431, P0420. These related codes typically originate from the same system modification and should be addressed together in the calibration.

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