# OBD2 engine codes explained in plain English

> Plain-English meanings for 144 common OBD2 / DTC engine codes (check engine light). Generic SAE P0xxx list with simple descriptions and drive-or-stop guidance from Carspel.

Canonical page: https://www.carspel.ca/en/engine-codes/

Check engine light on? Your OBD2 scanner shows a code like **P0300** or **P0420** — but what does it mean? This page gives **plain-language meanings** for **144** common generic SAE diagnostic trouble codes (DTCs) covering engine, emissions, and transmission.

These are **generic** codes (often P0xxx) shared across OBD2 vehicles — not every manufacturer-specific code a car can store. In the Carspel phone app, an engine health check with an ELM327 adapter explains codes on this list; other codes still appear with the code shown and no reviewed description yet.

## How to read an OBD2 / DTC code

A diagnostic trouble code is usually five characters. The letter is the system: P = powertrain (engine and transmission), C = chassis, B = body, U = network. A 0 in the second place marks a generic SAE code (same meaning on most brands); a 1 often marks a manufacturer-specific code outside this list.Common examples: P0300 (misfires), P0420 (catalytic converter), P0457 (often a loose gas cap). The table below adds drive-or-stop style guidance per code — not a shop diagnosis.

## Misfires & ignition

- **P0300** — Engine misfire detected, not narrowed to one cylinder. _Book service soon — stop if the light is flashing_
- **P0301** — Cylinder 1 misfire detected. _Book service soon — stop if the light is flashing_
- **P0302** — Cylinder 2 misfire detected. _Book service soon — stop if the light is flashing_
- **P0303** — Cylinder 3 misfire detected. _Book service soon — stop if the light is flashing_
- **P0304** — Cylinder 4 misfire detected. _Book service soon — stop if the light is flashing_
- **P0305** — Cylinder 5 misfire detected. _Book service soon — stop if the light is flashing_
- **P0306** — Cylinder 6 misfire detected. _Book service soon — stop if the light is flashing_
- **P0307** — Cylinder 7 misfire detected. _Book service soon — stop if the light is flashing_
- **P0308** — Cylinder 8 misfire detected. _Book service soon — stop if the light is flashing_
- **P0316** — Misfire detected in the first moments after starting. _Book service soon — stop if the light is flashing_
- **P0325** — Knock sensor fault (bank 1). _Book service soon_
- **P0327** — Knock sensor signal is lower than expected. _Book service soon_
- **P0328** — Knock sensor signal is higher than expected. _Book service soon_
- **P0350** — Ignition coil circuit fault, coil not identified. _Book service soon_
- **P0351** — Ignition coil A circuit fault. _Book service soon_
- **P0352** — Ignition coil B circuit fault. _Book service soon_
- **P0353** — Ignition coil C circuit fault. _Book service soon_
- **P0354** — Ignition coil D circuit fault. _Book service soon_
- **P0355** — Ignition coil E circuit fault. _Book service soon_
- **P0356** — Ignition coil F circuit fault. _Book service soon_
- **P0357** — Ignition coil G circuit fault. _Book service soon_
- **P0358** — Ignition coil H circuit fault. _Book service soon_

## Engine timing

- **P0011** — Camshaft timing is further ahead than expected (bank 1). _Book service soon_
- **P0014** — Camshaft timing is further behind than expected (bank 1). _Book service soon_
- **P0016** — Crankshaft and camshaft signals do not agree (bank 1, sensor A). _Book service soon_
- **P0017** — Crankshaft and camshaft signals do not agree (bank 1, sensor B). _Book service soon_
- **P0335** — Crankshaft position sensor fault. _Book service soon_
- **P0336** — Crankshaft position sensor signal is irregular. _Book service soon_
- **P0340** — Camshaft position sensor fault. _Book service soon_
- **P0341** — Camshaft position sensor signal is irregular. _Book service soon_

## Fuel mixture & air intake

- **P0087** — Fuel pressure is lower than the engine expects. _Book service soon_
- **P0100** — Airflow sensor reading is unreliable. _Book service soon_
- **P0101** — Airflow sensor reading is out of the normal range. _Book service soon_
- **P0102** — Airflow sensor signal is lower than expected. _Book service soon_
- **P0103** — Airflow sensor signal is higher than expected. _Book service soon_
- **P0106** — Intake pressure sensor reading is out of range. _Book service soon_
- **P0107** — Intake pressure sensor signal is lower than expected. _Book service soon_
- **P0108** — Intake pressure sensor signal is higher than expected. _Book service soon_
- **P0110** — Intake air temperature sensor fault. _Safe to drive_
- **P0111** — Intake air temperature reading is out of range. _Safe to drive_
- **P0112** — Intake air temperature signal is lower than expected. _Safe to drive_
- **P0113** — Intake air temperature signal is higher than expected. _Safe to drive_
- **P0171** — Engine is running leaner than expected (bank 1). _Book service soon_
- **P0172** — Engine is running richer than expected (bank 1). _Book service soon_
- **P0174** — Engine is running leaner than expected (bank 2). _Book service soon_
- **P0175** — Engine is running richer than expected (bank 2). _Book service soon_

## Oxygen sensors

- **P0130** — Oxygen sensor signal fault (bank 1, sensor 1). _Book service soon_
- **P0131** — Oxygen sensor signal is lower than expected (bank 1, sensor 1). _Book service soon_
- **P0132** — Oxygen sensor signal is higher than expected (bank 1, sensor 1). _Book service soon_
- **P0133** — Oxygen sensor is responding slower than expected (bank 1, sensor 1). _Book service soon_
- **P0134** — Oxygen sensor shows no activity (bank 1, sensor 1). _Book service soon_
- **P0135** — Oxygen sensor heater fault (bank 1, sensor 1). _Book service soon_
- **P0136** — Oxygen sensor signal fault (bank 1, sensor 2). _Book service soon_
- **P0137** — Oxygen sensor signal is lower than expected (bank 1, sensor 2). _Book service soon_
- **P0138** — Oxygen sensor signal is higher than expected (bank 1, sensor 2). _Book service soon_
- **P0140** — Oxygen sensor shows no activity (bank 1, sensor 2). _Book service soon_
- **P0141** — Oxygen sensor heater fault (bank 1, sensor 2). _Book service soon_
- **P0150** — Oxygen sensor signal fault (bank 2, sensor 1). _Book service soon_
- **P0151** — Oxygen sensor signal is lower than expected (bank 2, sensor 1). _Book service soon_
- **P0152** — Oxygen sensor signal is higher than expected (bank 2, sensor 1). _Book service soon_
- **P0153** — Oxygen sensor is responding slower than expected (bank 2, sensor 1). _Book service soon_
- **P0154** — Oxygen sensor shows no activity (bank 2, sensor 1). _Book service soon_
- **P0155** — Oxygen sensor heater fault (bank 2, sensor 1). _Book service soon_
- **P0156** — Oxygen sensor signal fault (bank 2, sensor 2). _Book service soon_
- **P0157** — Oxygen sensor signal is lower than expected (bank 2, sensor 2). _Book service soon_
- **P0158** — Oxygen sensor signal is higher than expected (bank 2, sensor 2). _Book service soon_
- **P0160** — Oxygen sensor shows no activity (bank 2, sensor 2). _Book service soon_
- **P0161** — Oxygen sensor heater fault (bank 2, sensor 2). _Book service soon_

## Catalytic converter

- **P0420** — Catalytic converter isn't cleaning exhaust as well as expected (bank 1). _Book service soon_
- **P0421** — Catalytic converter warm-up efficiency below expected (bank 1). _Book service soon_
- **P0430** — Catalytic converter isn't cleaning exhaust as well as expected (bank 2). _Book service soon_
- **P0431** — Catalytic converter warm-up efficiency below expected (bank 2). _Book service soon_

## Fuel tank & gas cap

- **P0440** — Fuel vapor system fault detected. _Safe to drive_
- **P0441** — Fuel vapor system isn't purging correctly. _Safe to drive_
- **P0442** — Small fuel vapor leak detected. _Safe to drive_
- **P0443** — Fuel vapor purge valve circuit fault. _Safe to drive_
- **P0446** — Fuel vapor vent control circuit fault. _Safe to drive_
- **P0449** — Fuel vapor vent valve or solenoid circuit fault. _Safe to drive_
- **P0451** — Fuel vapor pressure sensor reading is out of range. _Safe to drive_
- **P0455** — Larger fuel vapor leak detected. _Safe to drive_
- **P0456** — Very small fuel vapor leak detected. _Safe to drive_
- **P0457** — Gas cap may be loose, damaged, or missing. _Safe to drive_
- **P0460** — Fuel gauge sensor fault. _Safe to drive_
- **P0461** — Fuel gauge sensor reading is out of range. _Safe to drive_
- **P0462** — Fuel gauge sensor signal is lower than expected. _Safe to drive_
- **P0463** — Fuel gauge sensor signal is higher than expected. _Safe to drive_
- **P0464** — Fuel gauge sensor signal is inconsistent. _Safe to drive_

## Cooling & temperature

- **P0115** — Coolant temperature sensor fault. _Book service soon_
- **P0116** — Coolant temperature reading is out of range. _Book service soon_
- **P0117** — Coolant temperature signal is lower than expected. _Book service soon_
- **P0118** — Coolant temperature signal is higher than expected. _Book service soon_
- **P0125** — Engine is taking too long to reach normal operating temperature. _Safe to drive_
- **P0128** — Thermostat is stuck open. _Safe to drive_
- **P0217** — Engine coolant temperature is too high. _Stop driving_

## Throttle & idle

- **P0120** — Throttle position sensor fault. _Book service soon_
- **P0121** — Throttle position reading is out of range. _Book service soon_
- **P0122** — Throttle position signal is lower than expected. _Book service soon_
- **P0123** — Throttle position signal is higher than expected. _Book service soon_
- **P0505** — Idle speed control system fault. _Book service soon_
- **P0506** — Idle speed is lower than expected. _Book service soon_
- **P0507** — Idle speed is higher than expected. _Book service soon_

## Battery & charging

- **P0562** — Charging system voltage is low. _Book service soon_
- **P0563** — Charging system voltage is high. _Book service soon_

## Diesel soot filter

- **P2002** — Soot filter is trapping less than it should (bank 1). _Book service soon_
- **P2003** — Soot filter is trapping less than it should (bank 2). _Book service soon_
- **P242F** — Ash has built up in the soot filter. _Book service soon_
- **P244A** — Pressure across the soot filter is lower than expected (bank 1). _Book service soon_
- **P244B** — Pressure across the soot filter is lower than expected (bank 2). _Book service soon_
- **P2458** — A filter cleaning cycle ran longer than expected. _Book service soon_
- **P2459** — The soot filter is cleaning itself more often than it should. _Book service soon_
- **P2463** — Soot has built up in the filter. _Book service soon_

## Transmission & speed

- **P0500** — Vehicle speed sensor fault. _Book service soon_
- **P0501** — Vehicle speed sensor reading is out of range. _Book service soon_
- **P0700** — Transmission computer has detected a fault. _Book service soon_
- **P0705** — Gear selector position sensor fault. _Book service soon_
- **P0710** — Transmission fluid temperature sensor fault. _Book service soon_
- **P0715** — Transmission input speed sensor fault. _Book service soon_
- **P0720** — Transmission output speed sensor fault. _Book service soon_
- **P0725** — Engine speed signal to transmission is faulty. _Book service soon_
- **P0730** — Transmission isn't shifting into the correct gear ratio. _Book service soon_
- **P0740** — Torque converter lock-up fault. _Book service soon_
- **P0741** — Torque converter clutch isn't locking up as expected. _Book service soon_
- **P0742** — Torque converter clutch is stuck locked. _Book service soon_
- **P0743** — Torque converter clutch circuit electrical fault. _Book service soon_
- **P0750** — Shift solenoid A fault. _Book service soon_
- **P0755** — Shift solenoid B fault. _Book service soon_
- **P0760** — Shift solenoid C fault. _Book service soon_
- **P0765** — Shift solenoid D fault. _Book service soon_
- **P0770** — Shift solenoid E fault. _Book service soon_

## Engine computer

- **P0600** — Internal computer communication fault. _Book service soon_
- **P0601** — Engine computer memory error. _Book service soon_
- **P0602** — Engine computer programming error. _Book service soon_
- **P0603** — Engine computer memory retention fault. _Book service soon_
- **P0604** — Engine computer working memory (RAM) fault. _Book service soon_
- **P0605** — Engine computer program memory (ROM) fault. _Book service soon_
- **P0606** — Engine computer processor fault. _Book service soon_

## Other emission controls

- **P0401** — Exhaust gas recirculation system isn't flowing enough. _Book service soon_
- **P0402** — Exhaust gas recirculation system is flowing too much. _Book service soon_
- **P0403** — EGR valve circuit fault. _Book service soon_
- **P0404** — EGR valve position reading is out of range. _Book service soon_
- **P0405** — EGR position sensor signal is lower than expected. _Book service soon_
- **P0406** — EGR position sensor signal is higher than expected. _Book service soon_
- **P0410** — Secondary air injection system fault. _Safe to drive_
- **P0411** — Secondary air injection flow is incorrect. _Safe to drive_

## Frequently asked questions

### What is an OBD2 engine code (DTC)?

A diagnostic trouble code is a five-character code your vehicle's computer stores when it detects a fault. OBD2 scanners and phone apps with an ELM327 adapter read these codes so you can see why the check engine light came on.

### Does Carspel explain every engine code?

No. This page covers 144 reviewed generic SAE powertrain codes (engine, emissions, transmission). Manufacturer-specific and other DTCs may still appear in a reading with the code shown and no reviewed description yet.

### Can I keep driving with the check engine light on?

It depends on the code. The table below gives a default: safe to drive, book service soon, or stop driving. A flashing light with a misfire means stop. Several codes together can be more urgent than one alone.

### How do I read these codes with Carspel?

With a Bluetooth ELM327 OBD2 adapter, Carspel's phone engine health check (Ultimate plan) reads codes and explains ones on this list. You can also share a more detailed PDF with a mechanic: the same plain-language reading, plus technical detail such as stored, pending and permanent codes, battery voltage, coolant, fuel mixture, the VIN the car reports, emissions self-check status, and recent service on the vehicle. The PDF is not a repair record. See the User Guide, Ultimate Section 9, for connect steps.

Also available in French: https://www.carspel.ca/fr/engine-codes/