All Powertrain Emissions DTC Codes — Complete OBD-II Diagnostic Guide (2026)

This comprehensive reference covers every Powertrain Emissions diagnostic trouble code (DTC) — 28 codes total. Each code includes what triggers it, common symptoms, step-by-step diagnostic procedures, and repair guidance.

28DTC Codes

20Medium

8Low

Quick Reference — Powertrain Emissions Codes

DTC Code	Meaning	Severity	Common Makes
P0400	The engine control module detects that the EGR system is not moving the correct amount of exhaust gases back into the intake. The valve, passages, or sensor are not delivering the flow the computer expects.	medium	Toyota, Honda, Ford
P0401	The engine control module (ECM) has detected that the Exhaust Gas Recirculation (EGR) system is not delivering enough exhaust gases back into the intake. The restriction can be caused by a stuck valve, clogged passages, a vacuum/boost‑control problem, or a wiring fault.	medium	Toyota, Honda, Ford
P0402	The engine control module (ECM) has detected that more exhaust gas is being recirculated than the system expects. This usually means the EGR valve is stuck open, a vacuum leak, or a faulty flow sensor, causing too much exhaust to re‑enter the intake.	medium	Toyota, Honda, Ford
P0410	The engine control module has detected that the secondary‑air injection (SAI) system is not delivering the extra air needed during cold‑start enrichment. This leads to a richer mixture, higher emissions, and a illuminated check‑engine light.	medium	Toyota, Honda, Ford
P0411	The engine control module (ECM) has detected that the secondary‑air injection (SAI) system is delivering too little or too much air compared with the PCM’s command. The pump, valve, wiring, or sensor data are usually at fault.	medium	Toyota, Honda, Ford
P0420	The P0420 code means your catalytic converter is not cleaning exhaust gases as efficiently as it should. The downstream oxygen sensor detects that the catalyst is underperforming compared to the upstream sensor readings.	medium	Toyota, Honda, Ford
P0421	The P0421 code indicates that the warm-up catalyst efficiency is below the threshold for Bank 1, which means the catalytic converter is not functioning properly during the warm-up phase. This can lead to increased emissions and decreased fuel efficiency. The code is triggered when the engine control module (ECM) detects that the catalytic converter is not reaching the required temperature during the warm-up phase, which is typically between 400°C to 600°C.	medium	Toyota, Honda, Ford
P0430	The engine control module has determined that the catalytic converter on bank 2 is not cleaning the exhaust as efficiently as it should. The downstream oxygen sensor reports a higher‑than‑expected oxygen level, indicating the converter isn’t doing its job.	medium	Toyota, Honda, Ford
P0440	The engine control module has detected a problem with the evaporative emission (EVAP) system – the network that captures fuel vapors from the fuel tank and routes them to the engine for combustion. A fault means the system isn’t sealing or venting correctly, so vapors can escape or the system can’t be purged on command.	low	Toyota, Honda, Ford
P0441	The engine control module has detected that the EVAP purge valve is allowing too much fuel vapor into the intake, or not closing properly. This abnormal purge flow trips the P0441 code and may affect emissions compliance.	low	Toyota, Honda, Ford
P0442	The engine control module has found a small leak in the evaporative emissions (EVAP) system. This system captures fuel vapors from the tank and stores them in a charcoal canister. A tiny leak lets vapors escape, triggering the P0442 code.	low	Toyota, Honda, Ford
P0443	The engine control module has detected a problem with the electrical circuit that operates the EVAP purge control valve. The valve may be stuck open, stuck closed, or the wiring/connector may be shorted or open, preventing the system from properly purging fuel vapors.	medium	Toyota, Honda, Ford
P0446	The engine control module has detected a problem with the vent control circuit of the evaporative emissions (EVAP) system. The vent valve or its wiring isn’t opening or closing when the computer commands it, so fuel vapors cannot be vented properly.	low	Toyota, Honda, Ford
P0449	The engine control module has detected a problem with the vent valve or its control circuit in the evaporative‑emission (EVAP) system. The valve may not open/close when commanded, or the wiring may be shorted, open, or have abnormal resistance.	medium	Toyota, Honda, Ford
P0451	The engine control module has detected that the EVAP‑system pressure sensor is reporting values outside its calibrated range. The cause is usually a faulty sensor, damaged wiring, or an over‑pressurized EVAP system.	medium	Toyota, Honda, Ford
P0452	The engine control module has detected that the pressure sensor in the evaporative emission (EVAP) system is reporting a voltage lower than the expected range. In plain English, the sensor that tells the computer how much pressure is in the fuel‑vapour tank isn’t sending a strong enough signal.	medium	Toyota, Honda, Ford
P0455	The engine control module has sensed a large leak in the evaporative emissions (EVAP) system. The leak is big enough that the system can’t hold pressure during the self‑test, so the PCM sets the P0455 code.	medium	Toyota, Honda, Ford
P0456	The engine control module has sensed a tiny leak in the evaporative emissions (EVAP) system, usually less than 0.05 psi. The leak lets fuel vapors escape, triggers the check‑engine light, and can prevent the EVAP monitor from completing.	low	Toyota, Honda, Ford
P0457	The P0457 code signals an evaporative‑emission (EVAP) system leak that the power‑train control module (PCM) detects during its self‑check. The most common source is a loose, damaged, or missing fuel‑cap, but the leak can also originate from hoses, the canister, purge or vent valves, or the fuel‑tank itself.	low	Toyota, Honda, Ford
P0496	The PCM has detected that the EVAP purge valve is allowing more vapor flow than expected during the purge cycle, indicating a possible stuck-open valve or wiring issue.	medium	Toyota, Honda, Ford
P0498	The PCM has detected that the vent valve in the evaporative emissions (EVAP) system is not receiving enough voltage or signal. This usually means a low‑voltage condition, an open circuit, or a faulty valve, preventing fuel vapors from venting properly.	low	Toyota, Honda, Ford
P1456	The P1456 code indicates a gross leak in the Evaporative Emission Control System (EVAP) related to the fuel tank. This system prevents fuel vapors from escaping into the atmosphere. A gross leak means a significant amount of fuel vapor is escaping, which can cause performance issues and increased emissions.	medium	Honda, Toyota, Ford
P1457	The engine control module has sensed that the evaporative emissions (EVAP) control canister is leaking. Fuel vapors are escaping from the canister or its plumbing instead of being stored for later purge.	low	Toyota, Honda, Ford
P2002	The P2002 code indicates that your vehicle's diesel particulate filter (DPF) is not functioning efficiently. The DPF is designed to capture soot and other pollutants from the exhaust gas. When the filter becomes clogged or fails, it can cause this code to appear. This issue can lead to decreased engine performance, reduced fuel efficiency, and increased emissions.	medium	Toyota, Honda, Ford
P2096	The P2096 code indicates that the engine control module (ECM) has detected a lean fuel mixture in the exhaust gases after the catalytic converter (Bank 1). This suggests that there's too much air and not enough fuel in the exhaust gases, which can be caused by various factors, including faulty oxygen sensors, clogged fuel injectors, or vacuum leaks.	medium	Toyota, Honda, Ford
P2097	P2097 tells the engine computer that the fuel trim after the catalytic converter on bank 1 is running too rich. In plain language, the engine is adding more fuel than needed downstream of the catalyst, which can foul the catalyst and hurt fuel economy.	medium	Toyota, Honda, Ford
P2440	The P2440 code indicates that the engine control module (ECM) has detected that the secondary air injection switching valve is stuck open on bank 1. This valve helps reduce emissions by injecting air into the exhaust system. A stuck open valve can cause the engine to run rich, leading to decreased performance and fuel efficiency.	medium	Toyota, Honda, Ford
SYMPTOM-FAILED-EMISSIONS	The powertrain control module has determined that the vehicle did not meet the required emissions standards during a recent test. It usually means a sensor, leak, or catalyst isn’t working within spec.	medium	Toyota, Honda, Ford

Detailed DTC Code Guides

P0400: The engine control module detects that the EGR system is not moving the correct amount of exhaust gases back into the intake. The valve, passages, or sensor are not delivering the flow the computer expects.

medium ⏱️ 30‑60 minutes ⚠️ You can keep driving, but expect reduced low‑end power, higher fuel use, and a likely emissions‑test failure.

Fix OBD‑II code P0400: Exhaust Gas Recirculation (EGR) Flow Malfunction. Step‑by‑step diagnosis, repair tips, cost guide, and safety advice.

Diagnostic steps:

Quick visual check
Inspect EGR valve and passages
Test EGR valve operation
...see all 4 steps →

Detailed DTC Code Guides

Understanding Powertrain Emissions Codes

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