Everything You Need to Know about Check Engine Codes

Is your car’s check engine light on?
Not sure what it means?

Several problems can trigger this warning light, making diagnosis tricky, especially when there are no other clear symptoms. Fortunately, check engine codes provide specific insights into the problem.

Curious to know more?

To help you diagnose the issue, we’ll explain the most common codes and how to extract them. We’ll also answer some common queries that you may have related to check engine codes.

This Article Contains:

Common Diagnostic Trouble Codes for Check Engine Lights
What Do Other OBD 2 Codes Mean?
How to Extract a Check Engine Light Code (Step-By-Step)
3 FAQs on Check Engine Light Codes

Common Diagnostic Trouble Codes for Check Engine Lights

Knowing every diagnostic trouble code (or OBD II code) seems impossible. But there are some you can get familiar with to help you understand your car’s issues better. Mostly, a powertrain code (P-code) will trigger the check engine light.

Here are some of the most common diagnostic trouble codes given by the OBD system (or on-board diagnostics system):

1. P0000-P0099: Fuel Metering, Air Metering, and Auxiliary Emission Controls

These OBD II codes indicate issues with fuel volume or pressure regulators, turbochargers, superchargers, and emissions-related sensors. Here are some examples:

P0001: Fuel Volume Regulator Control Circuit/Open. There’s a faulty fuel pressure regulator or wiring issue.
P0040: Upstream Oxygen Sensors Swapped from Bank to Bank. There’s a wiring mix-up or an installation error.
P0068: Throttle Body Airflow Performance Issue. The Engine Control Module (ECM) detects inconsistencies between the Mass Airflow Sensor (MAF) and throttle position.

2. P0100-P0199: Fuel and Air Metering

A powertrain code in the P0100-P0199 range alerts vehicle owners about fuel and air metering as well as their car’s oxygen levels. Here are some examples:

P0171: System too Lean (Bank 1). The fuel system of the vehicle has either too little or too much air.
P0172: System too Rich (Bank 1). The Fuel system has excessive gasoline and insufficient oxygen in the air-fuel mixture.
P0173: Fuel Trim Malfunction (Bank 2). The air-fuel ratio is either too lean or too rich.
P0174: System too Lean (Bank 2). The MAF sensor is reporting very little air in the air-fuel mixture.
P0130: Oxygen Sensor Circuit Malfunction (Bank 1, Sensor 1). There’s no oxygen sensor (O2 sensor) activity detected.
P0131: O2 Sensor Circuit Low Voltage (Bank I Sensor I). There’s improper voltage from the O2 sensor.
P0133: O2 Sensor Circuit Slow Response (Bank 1, Sensor 1). The O2 sensor isn’t changing its voltage output quickly enough to the changing air-fuel ratio.

3. P0200-P0299: Fuel and Air Metering (Fuel Injector Circuit)

An engine code in the P0200-P0299 range relates to the fuel injector circuit. Here are a few examples :

P0200: Fuel Injector Circuit Malfunction. This is a generic code that indicates a problem in the fuel injector circuit.
P0201: Fuel Injector Circuit Malfunction (Cylinder 1). This is a specific code indicating which cylinder is affected.

4. P0300-P0399: Ignition System and Misfire

OBD II codes P0300-P0399 indicate engine misfire or issues with the ignition system. Here are some examples:

P0300: Random/Multiple Cylinder Misfire Detected. Indicates misfires across multiple cylinders, possibly due to issues with spark plugs, ignition coils, and fuel injectors.
P0301: Cylinder 1 Misfire Detected. Points to a misfire detected in cylinder 1 of the engine.
P0351: Ignition Coil “A” Primary/Secondary Circuit Malfunction. There’s a faulty ignition coil, wiring issues, or a problem in the ignition module.

5. P0400-P0499: Auxiliary Emission Controls

Codes in this range relate to the exhaust gas recirculation (EGR) system, evaporative emissions control system (EVAP), and secondary air injection. Here are some examples:

P0401: Exhaust gas recirculation (EGR) flow is insufficient. It can be due to a clogged EGR valve or a faulty sensor.
P0420: Catalyst System Efficiency Below Threshold (Bank 1). The catalytic converter isn’t working optimally, or there’s a faulty oxygen sensor.
P0430: Catalyst System Efficiency Below Threshold (Bank 2). A generic code that’s triggered when there’s a problem in the catalyst system.
P0440: Evaporative Emission Control System Malfunction. Indicates a leak or failure in fuel vapor containment.

6. P0500-P0599: Vehicle Speed Control and Idle Control System

These codes indicate issues with idle control systems, vehicle speed sensors, throttle actuator control, and cruise control. Some examples include:

P0500: Vehicle Speed Sensor Malfunction. The ECM isn’t receiving a proper signal from the speed sensor.
P0505: Idle Control System Malfunction. The engine idle speed is fluctuating due to idle air control valve or throttle body issues.
P0562: Low System Voltage. The battery or alternator may be underperforming.

7. P0600-P0699: Computer Output Circuit

Codes in this range indicate problems with the ECM, miscommunication between control modules, or software-related faults. Let’s look at a few examples:

P0601: Internal Control Module Memory Check Sum Error. Indicated a possible ECM fault.
P0606: ECM/PCM Processor Fault. Hints at internal failure in the powertrain control module (PCM).
P0610: Control Module Vehicle Options Error. Indicated software mismatch or corrupted data.

8. P0700-P0799: Transmission Controls

Codes P0700-P0799 relate to automatic transmission operation and gear-shifting. Here are some examples:

P0700: Transmission Control System Malfunction. A generic code indicating an issue stored in the transmission control module.
P0715: Input/Turbine Speed Sensor “A” Circuit Malfunction. Triggers when the signal from the transmission input sensor is erratic or missing.
P0740: Torque Converter Clutch (TCC) Circuit/Open. Triggers when TCC is not engaging or slipping.

9. P0800-P0899: Transmission Controls (Auxiliary)

Typically, a code within this range is a manufacturer-specific code related to the supplementary transmission system. Here are a few:

P0826: Up and Down Shift Switch Circuit. Indicated problem with the shift switch input circuit used in manual-mode automatics or paddle-shift systems.
P0841: Transmission fluid Pressure Sensor/Switch A Circuit Range/Performance. Triggered when the signal is outside the expected range.
P0882: Transmission Control Module Power Input Signal Low. Triggers when the power supply to the transmission control module is interrupted.

10. P0900-P0999: Transmission and Gear Shift Control

These codes focus on gear shift actuator circuits and other transmission control components. Let’s look at some common examples:

P0901: Clutch Actuator Circuit Range/Performance. Indicates an issue with the actuator control for clutch engagement.
P0960: Pressure Control Solenoid “A” Control Circuit/Open. It hints at an electrical problem in the pressure control solenoid “A” circuit.
P0980: Shift Solenoid “C” Control Circuit High. Triggers due to an electrical fault in the shift solenoid.

11. P1000-P1999: Manufacturer-Specific Codes

These codes vary by make and model, specific to the manufacturers and vehicle systems. Here are some common ones:

P1131 (Ford): Lack of HO2S-11. Indicated that the upstream oxygen sensor located on Bank 1 is not showing expected activity.
P1155 (Toyota): Air/fuel Sensor Heater Circuit Malfunction (Bank 2, Sensor 1). Triggers when the malfunctioning A/F sensor heater circuit is affecting the feedback fuel control.
P1259 (Honda): Variable Valve Timing and Lift Electronic Control (VTEC) System Malfunction. Triggers when the Variable Valve Timing system (VVT) is not engaging properly.

12. P2000-P2199: Air/Fuel and Emissions (Generic)

P2000-P2199 codes include nitrogen oxide (NOx) sensors, air-fuel ratio sensors, and exhaust after-treatment systems. Let’s take a look:

P2002: Diesel Particulate Filter Efficiency Below Threshold. Indicates the filter may be clogged or sensor error.
P2096: Post-Catalyst Fuel Trim System Too Lean (Bank 1). Hints at an exhaust leak or a faulty O2 sensor.
P2195: O2 Sensor Signal Biased/Stuck Lean (Bank 1, Sensor 1). Triggers when the sensor consistently reports low voltage.

13. P2200-P2299: Emission Controls (Diesel and Gasoline)

This range of codes deals with Selective Catalytic Reduction (SCR) systems, Nitrogen Oxide (NOx) sensors, and Diesel Particulate Filter (DPF) systems. Common examples include:

P2201: NOx Sensor Circuit Range/Performance (Bank 1, Sensor 1). Indicates that the sensor is out of the expected range.
P2263: Turbo/Super Charger Boost System Performance. Triggers when low or no boost is detected during load.
P2293: Fuel Pressure Regulator 2 Performance. Triggers when the fuel pressure is too high or too low.

14. P2300-P2399: Ignition System (Secondary)

These codes cover issues related to ignition coil control, secondary ignition circuits, and ignition signal errors. Here are a few examples:

P2301: Ignition Coil A Primary Control Circuit High. Triggers when the voltage is too high for coil A.
P2310: Ignition Coil F Secondary Circuit. Indicates an issue with the coil or associated circuit.
P2335: Ignition Coil K Secondary Circuit. Triggers when the signal to ignition coil K is out of range.

15. P2400-P2499: Evaporative Emission System

Codes within the P2400 range relate to fuel vapor leak detection, fuel tank pressure sensors, and EVAP pump performance. Here are some common ones:

P2401: EVAP Leak Detection Pump Control Circuit Low. Indicates that the leak detection pump is not receiving enough voltage.
P2413: Exhaust Gas Recirculation System Performance Issue. Hints that the EGR system isn’t responding as expected.
P2459: Diesel Particulate Filter Regeneration Frequency Issue. Triggers when the regeneration is occurring too often.

16. P2500-P2599: Engine and Transmission Electrical

This range includes charging systems, alternator control, and powertrain sensors. Here are some common codes:

P2502: Low Charging System Voltage. Triggers when the alternator is not supplying enough voltage.
P2562: Turbocharger Boost Control Position Sensor Circuit. Indicates the sensor reading is out of range.
P2585: Fuel Additive Control Module Warning Lamp Circuit. Indicates a fault in the warning lamp circuit for the Fuel Additive Control Module.

17. P2600-P2699: Additional Engine Controls

An engine code within this range covers engine coolant pumps, glow plug modules, and other auxiliary functions. These examples are quite common:

P2600: Coolant Pump Control Circuit/Open. Triggers when the coolant pump isn’t receiving power.
P2610: ECM/PCM Internal Engine Off Timer Performance. Triggers when there’s a malfunction in its internal engine-off timer.
P2681: Engine Coolant Bypass Valve Control Circuit High. Indicates an electrical issue in bypass valve operation.

18. P2700-P2899: Transmission Hydraulic Control

Codes in this range cover issues with transmission fluid pressure sensors, shift solenoids, and the hydraulic pump. Here are some examples:

P2701: Transmission Friction Element A Apply Time Range/Performance. Triggers when shifting is delayed or harsh.
P2757: Torque Converter Clutch Pressure Control Solenoid Performance/Stuck Off. Triggers when the converter clutch is not engaging properly.
P2810: Pressure Control Solenoid “H” Performance or Stuck Off. Hints at issues with pressure regulation.

19. P2900-P2999: Intake Air and Fuel Delivery

These codes cover intake air heater performance and air-fuel mixture delivery faults. Let’s take a look:

P2900: Intake Airflow Performance Issue. Hints at sensor disagreement or airflow obstruction.
P2999: Turbocharger/Supercharger Low Boost Condition. Triggers when the turbo is underperforming or leaks are present.

20. P3000-P3400+: Advanced Engine Management or Manufacturer Specific Code

High-numbered codes often relate to advanced engine technologies or manufacturer-specific use. These examples are quite common:

P3011 (Toyota): Battery Block 1 Becomes Weak. Triggers when one of the battery blocks in the hybrid system has a lower voltage than expected, which is often an aging cell.
P3400 (Honda, GM): Cylinder Deactivation System Bank. Indicates a problem in the variable cylinder management system, such as low oil pressure or a failed rocker arm actuator.

While P codes typically trigger the check engine light, there are some other important codes you should know about.

Let’s take a look.

What Do Other OBD 2 Codes Mean?

Here are some other types of codes you may encounter:

1. BXXXX-Codes

Any B error code relates to body control modules, which manage functions like lighting, airbags, seat control, and other interior features. Here are some examples:

B0001-B0099: Airbag and restraint systems
B0100-B0199: Body control module and passenger comfort
B0200-B0299: Climate control systems
B0300-B0399: Lighting and accessory circuits
B0400-B0499: Power accessories
B0500-B0599: Instrument panel and display issues
B1000-B1999: Manufacturer-specific body system issues

2. CXXXX-Codes

Any C error code is associated with the chassis system, including components like ABS (Anti-lock Brake System), traction control, and stability control. Let’s take a look:

C0001-C0099: Brake hydraulic system
C0100-C0199: Suspension system (e.g., ride height sensors, control arms)
C0200-C0299: Steering systems (e.g., electronic steering assist)
C0300-C0399: Driveline and axle-related issues
C0500-C0599: Tire pressure monitoring system (TPMS)
C1000-C1999: Manufacturer-specific chassis faults

3. UXXXX-Codes

U-codes typically indicate communication faults between modules within the vehicle’s network. Here are some common ones:

U0001-U0099: Communication bus faults such as CAN (Controller Area Network)
U0100-U0199: Lost communication with specific control modules
U0200-U0299: Communication errors with body control modules
U0300-U0399: Software incompatibility issues between modules
U0400-U0499: Invalid data received from modules
U1000-U1999: Manufacturer-specific communication faults

Now that you understand OBD II codes, we’ll explain how you can access them when your check engine light appears.

How to Extract a Check Engine Light Code (Step-By-Step)

The check engine light turns on when your OBD system detects an issue or malfunction.

In such cases, you need to extract and read the generated diagnostic trouble code (DTC code) to determine what triggered your check engine light. However, doing so requires an OBD 2 scan tool or fault code reader, which most drivers don’t have. So, you’ll likely need to contact a mechanic.

Depending on your OBD scanner type, the tool will either:

Provide one-liner definitions of the check engine codes (OBD 2 scanner) or
Display a diagnostic trouble code that’s five characters long (code reader)

Now let’s understand how a mechanic would extract check engine codes with an OBD II scanner:

Find your car’s OBD port (or OBD-II diagnostic connector). It’s usually under the dashboard on the driver’s side, near the pedals. To connect the OBD II scanner or code reader to the port, they’ll use a 16-pin connector.

Plug one end of the connector into the OBD port or diagnostic connector and the other into the diagnostic tool. The scan tool will switch on when it’s plugged in. If it doesn’t, they’ll turn on the ignition to power it.

With the OBD scanner on, they’ll read the check engine codes on the computer. They’ll follow the scan tool’s user instructions on how to operate it. It’ll mostly ask them to navigate to “Read Codes.”

They’ll note each DTC code the OBD2 scanner displays. If there are many check engine codes, the scan tool will cycle through them, or the mechanic can press a button to view one fault code after another.

Still have some unanswered questions about check engine codes?
Keep reading.

3 FAQs on Check Engine Light Codes

Here are the answers to some commonly asked check engine light questions:

1. Can You Drive with the Check Engine Light On?

If your check engine light comes on while you’re on the move, don’t panic. It doesn’t always mean you need an auto repair. Sometimes, it may even come temporarily due to a loose gas cap.

To understand the gravity, check if your vehicle is behaving any differently from usual. For example, a drop in fuel economy, even after filling up your fuel tank, may indicate a faulty oxygen sensor. If your engine is rough idling, it may be because of a spark plug issue or problems with fuel injectors.

If you’re unsure of the root cause, it’s best to get your vehicle checked by a mechanic as soon as possible.

However, if the check engine light isn’t just illuminated but flashing, you should immediately pull over and contact a mechanic. This indicates a severe issue, like a misfire, which can harm your engine or catalytic converter.

2. How Do You Clear an OBD II Trouble Code?

Clearing an OBD code requires resolving the issue triggering the warning light. This may be simple in some cases (like a loose gas cap) or more complex in others (like an engine misfiring). It is best to take your vehicle to a mechanic for a thorough diagnosis and repair.

On the off-chance your warning light doesn’t clear after resolving the issue, you can use an OBD-II scanner to clear the code. However, you should only do this if you’re certain you’ve fixed the problem.

3. Does the OBD 2 Scanner Work with All Cars?

The United States requires all cars manufactured from 1996 onwards to be OBD2 compliant. Older vehicles (pre-1996) typically use OBD1, which requires a different diagnostic tool.

Additionally, newer vehicles, especially hybrid and electric cars, may have different systems requiring specialized scanners.

Get Expert Help to Clear Your Check Engine Codes Fast

Check engine codes are essential for pinpointing a problem when something goes wrong with your vehicle.

However, without a scanner, you won’t be able to access the OBD II trouble code. In addition, you’ll need a professional to properly understand what the code means and repair the issue.

That’s where AutoNation Mobile Service steps in.

Our expert mobile mechanics can extract your problem code, diagnose the issue, and repair it from your driveway. We also offer transparent pricing, easy online bookings, and a 12-month, 12,000-mile warranty on all repairs.