Block of codes
P04xx codes: auxiliary emission controls
This block brings together the codes from P0400 to P04AA in the glossary. Open yours to see what it means, its causes and whether you can keep driving.
Reviewed by Daniel Morales, founder of Reprorace SL, on
What this block covers
Emission control
The catalytic converter, oxygen sensors, EGR, fuel vapor system (EVAP), particulate filter and NOx reduction clean the exhaust. A fault here raises pollution and may make the car fail its inspection; left alone, some end in a bigger fault or in limp-home mode.
Engine (mechanical, cooling and lubrication)
The engine's mechanics, timing (camshaft and crankshaft), cooling and lubrication. Many of these codes check that the engine is in time and at the right temperature.
Fuel and air metering
The engine measures the incoming air and meters the fuel so the mixture is right; the throttle, the accelerator pedal and the turbo are here too. A fault usually shows as higher fuel use, jerking, lack of power or hard starting.
The 163 codes of the block
- P0400EGR A flow: malfunction
- P0401EGR A flow: insufficient flow detected
- P0402EGR A flow: excessive flow detected
- P0403EGR A, control circuit open
- P0404EGR A, control circuit: range/performance
- P0405EGR sensor A, circuit: signal low
- P0406EGR sensor A, circuit: signal high
- P0407EGR sensor B, circuit: signal low
- P0408EGR sensor B, circuit: signal high
- P0409EGR sensor A, circuit: malfunction
- P040AEGR temperature sensor A, circuit: malfunction
- P040BEGR temperature sensor A, circuit: range/performance
- P040CEGR temperature sensor A, circuit: signal low
- P040DEGR temperature sensor A, circuit: signal high
- P040FEGR temperature sensor A/B: correlation fault
- P0410AIR system A: malfunction
- P0411AIR system A: incorrect flow detected
- P0412AIR system switching valve A, circuit: malfunction
- P0413AIR system switching valve A, circuit open
- P0414AIR system switching valve A, circuit: short circuit
- P0415AIR system switching valve B, circuit: malfunction
- P0416AIR system switching valve B, circuit open
- P0417AIR system switching valve B, circuit: short circuit
- P0419AIR system control B, circuit: malfunction
- P041AEGR temperature sensor B, circuit: malfunction
- P041BEGR temperature sensor B, circuit: range/performance
- P041CEGR temperature sensor B, circuit: signal low
- P041DEGR temperature sensor B, circuit: signal high
- P041EEGR temperature sensor B, circuit: intermittent/erratic
- P041FAIR system switching valve A, circuit: signal low
- P0420Catalyst system (bank 1): efficiency below threshold
- P0421Catalyst 1 (bank 1): efficiency below threshold
- P0422Catalyst 2 (bank 1): efficiency below threshold
- P0423Heated catalyst (bank 1): efficiency below threshold
- P0424Heated catalyst temperature (bank 1): below threshold
- P0425Catalyst temperature sensor (bank 1, sensor 1), circuit: malfunction
- P0426Catalyst temperature sensor (bank 1, sensor 1), circuit: range/performance
- P0427Catalyst temperature sensor (bank 1, sensor 1), circuit: signal low
- P0428Catalyst temperature sensor (bank 1, sensor 1), circuit: signal high
- P0429Catalyst heater (bank 1), control circuit open
- P042ACatalyst temperature sensor (bank 1, sensor 2), circuit: malfunction
- P042BCatalyst temperature sensor (bank 1, sensor 2), circuit: range/performance
- P042CCatalyst temperature sensor (bank 1, sensor 2), circuit: signal low
- P042DCatalyst temperature sensor (bank 1, sensor 2), circuit: signal high
- P042EEGR A control: stuck open
- P042FEGR A control: stuck closed
- P0430Catalyst system (bank 2): efficiency below threshold
- P0431Catalyst 1 (bank 2): efficiency below threshold
- P0432Catalyst 2 (bank 2): efficiency below threshold
- P0433Heated catalyst (bank 2): efficiency below threshold
- P0434Heated catalyst temperature (bank 2): below threshold
- P0435Catalyst temperature sensor (bank 2, sensor 1), circuit: malfunction
- P0436Catalyst temperature sensor (bank 2, sensor 1), circuit: range/performance
- P0437Catalyst temperature sensor (bank 2, sensor 1), circuit: signal low
- P0438Catalyst temperature sensor (bank 2, sensor 1), circuit: signal high
- P0439Catalyst heater (bank 2), control circuit open
- P043ACatalyst temperature sensor (bank 2, sensor 2), circuit: malfunction
- P043BCatalyst temperature sensor (bank 2, sensor 2), circuit: range/performance
- P043CCatalyst temperature sensor (bank 2, sensor 2), circuit: signal low
- P043DCatalyst temperature sensor (bank 2, sensor 2), circuit: signal high
- P043EEVAP system leak detection reference orifice low flow: malfunction
- P043FEVAP system leak detection reference orifice high flow: malfunction
- P0440EVAP system: malfunction
- P0441EVAP system incorrect purge flow: malfunction
- P0442EVAP system: small leak detected
- P0443EVAP system purge control valve A, circuit: malfunction
- P0444EVAP system purge control valve A, circuit open
- P0445EVAP system purge control valve A, circuit: short circuit
- P0446EVAP system vent, control circuit: malfunction
- P0447EVAP system vent, control circuit open
- P0448EVAP system vent, control circuit: short circuit
- P0449EVAP system vent valve, control circuit open
- P044FAIR system switching valve A, circuit: signal high
- P0450EVAP system pressure sensor/switch A, circuit: malfunction
- P0451EVAP system pressure sensor/switch A, circuit: range/performance
- P0452EVAP system pressure sensor/switch A, circuit: signal low
- P0453EVAP system pressure sensor/switch A, circuit: signal high
- P0454EVAP system pressure sensor/switch A, circuit: intermittent
- P0455EVAP system: large leak detected
- P0456EVAP system: very small leak detected
- P0457EVAP system: leak detected (fuel cap loose or missing)
- P0458EVAP system purge control valve A, circuit: signal low
- P0459EVAP system purge control valve A, circuit: signal high
- P045AEGR B, control circuit: malfunction
- P045BEGR B, control circuit: range/performance
- P045CEGR B, control circuit: signal low
- P045DEGR B, control circuit: signal high
- P045EEGR B control: stuck open
- P045FEGR B control: stuck closed
- P0460Fuel level sensor A, circuit: malfunction
- P0461Fuel level sensor A, circuit: range/performance
- P0462Fuel level sensor A, circuit: signal low
- P0463Fuel level sensor A, circuit: signal high
- P0464Fuel level sensor A, circuit: intermittent
- P0465EVAP purge flow sensor, circuit: malfunction
- P0466EVAP purge flow sensor, circuit: range/performance
- P0467EVAP purge flow sensor, circuit: signal low
- P0468EVAP purge flow sensor, circuit: signal high
- P0469EVAP purge flow sensor, circuit: intermittent
- P046ACatalyst temperature sensor 1/2 (bank 1): correlation fault
- P046BCatalyst temperature sensor 1/2 (bank 2): correlation fault
- P046CEGR sensor A, circuit: range/performance
- P046DEGR sensor A, circuit: intermittent/erratic
- P046EEGR sensor B, circuit: range/performance
- P046FEGR sensor B, circuit: intermittent/erratic
- P0470Exhaust pressure sensor A, circuit: malfunction
- P0471Exhaust pressure sensor A, circuit: range/performance
- P0472Exhaust pressure sensor A, circuit: signal low
- P0473Exhaust pressure sensor A, circuit: signal high
- P0474Exhaust pressure sensor A, circuit: intermittent/erratic
- P0475Exhaust pressure control valve A: malfunction
- P0476Exhaust pressure control valve A: range/performance
- P0477Exhaust pressure control valve A: signal low
- P0478Exhaust pressure control valve A: signal high
- P0479Exhaust pressure control valve A: intermittent
- P047AExhaust pressure sensor B, circuit: malfunction
- P047BExhaust pressure sensor B, circuit: range/performance
- P047CExhaust pressure sensor B, circuit: signal low
- P047DExhaust pressure sensor B, circuit: signal high
- P047EExhaust pressure sensor B, circuit: intermittent/erratic
- P047FExhaust pressure control valve A: stuck open
- P0480Fan 1, control circuit: malfunction
- P0481Fan 2, control circuit: malfunction
- P0482Fan 3, control circuit: malfunction
- P0483Fan rationality check: malfunction
- P0484Fan circuit current: too high
- P0485Fan power/ground, circuit: malfunction
- P0486EGR sensor B, circuit: malfunction
- P0487EGR throttle, control circuit A open
- P0488EGR throttle, control circuit A: range/performance
- P0489EGR A, control circuit: signal low
- P048AExhaust pressure control valve A: stuck closed
- P048BExhaust pressure control valve A position sensor/switch, circuit: malfunction
- P048CExhaust pressure control valve A position sensor/switch, circuit: range/performance
- P048DExhaust pressure control valve A position sensor/switch, circuit: signal low
- P048EExhaust pressure control valve A position sensor/switch, circuit: signal high
- P048FExhaust pressure control valve A position sensor/switch, circuit: intermittent/erratic
- P0490EGR A, control circuit: signal high
- P0491AIR system (bank 1): insufficient flow
- P0492AIR system (bank 2): insufficient flow
- P0493Fan: overspeed
- P0494Fan 1: underspeed
- P0495Fan 1: overspeed
- P0496EVAP system high purge flow: malfunction
- P0497EVAP system low purge flow: malfunction
- P0498EVAP system vent valve, control circuit: signal low
- P0499EVAP system vent valve, control circuit: signal high
- P049BEGR B flow: insufficient flow detected
- P049CEGR B flow: excessive flow detected
- P049DEGR A control position: learning limit exceeded
- P049EEGR B control position: learning limit exceeded
- P049FExhaust pressure control valve B: malfunction
- P04A0Exhaust pressure control valve B: range/performance
- P04A1Exhaust pressure control valve B: signal low
- P04A2Exhaust pressure control valve B: signal high
- P04A3Exhaust pressure control valve B: intermittent
- P04A4Exhaust pressure control valve B: stuck open
- P04A5Exhaust pressure control valve B: stuck closed
- P04A6Exhaust pressure control valve B position sensor/switch, circuit: malfunction
- P04A7Exhaust pressure control valve B position sensor/switch, circuit: range/performance
- P04A8Exhaust pressure control valve B position sensor/switch, circuit: signal low
- P04A9Exhaust pressure control valve B position sensor/switch, circuit: signal high
- P04AAExhaust pressure control valve B position sensor/switch, circuit: intermittent/erratic
Other blocks
Read your car's fault codes on your phone
With an ECO-LITE in the OBD socket you see the codes in your account, with the data captured when the fault happened, and your workshop can check them remotely, always with your permission.
Keep reading
- OBD fault codes: what each one means
- Check engine light on: what to do
- How to read and clear your car's fault codes
- Will your car pass its MOT or inspection with the engine light on?
- Wi-Fi OBD2 reader: which one to choose
- Reading fault codes by car make
- Remote OBD diagnostics: what it is, how it works and what it can't do
- Vehicle diagnostics glossary