The Ultimate OBD Codes Guide and OBD Codes PDF List

Onboard diagnostics (OBD) codes are the gateway to understanding issues with your vehicle’s components and systems. Like doctors diagnose illnesses by interpreting symptoms, mechanics leverage OBD codes to pinpoint problems under your car or truck’s hood.

Important Headings

We’ve all seen the “check engine” light glaring from our dashboards. An illuminated engine indicator lamp means that the onboard computer (called the electronic control module/ECM) embedded in your vehicle has logged a diagnostic trouble code (DTC) corresponding to one or more detected system malfunctions.

But what do these codes signify? How can we decipher their cryptic alphanumeric combinations to reveal meaningful insights into our vehicle’s health? This article will explore the basics to navigate the intriguing universe of OBD codes confidently.

Here are the Key OBD Code Takeaways:

  • They offer early identification of emerging vehicle faults to prevent cascading damage
  • Freeze frame data enhances troubleshooting by capturing operating scenarios when code is triggered
  • Pending codes reveal intermittent issues that storing only permanent DTCs would miss
  • Code clearing without addressing underlying failure risks instantly re-logging unfixed faults
  • Factory-level scanners unlock advanced capabilities like releasing permanent code memory locks
  • Even without a MIL light, routinely scanning for pending codes helps prevent surprises

So embrace the incredible early warning communications system onboard that OBD represents. Build knowledge, analyze supportive test parameters, troubleshoot proactively, drive strategically, scan regularly, and maintain preventatively.

The Evolution of OBD Codes: A Historical Perspective

Onboard diagnostics have come a long way since the first OBD framework rolled off the assembly line in the 1980s.

Before 1996, each automaker had its proprietary pre-OBD-II systems with non-standard codes and connectors. For example, GM utilized the ALDL (Assembly Line Diagnostic Link) interface to pull codes on their vehicles pre-1996.

It was a discordant mess for technicians who had to stock Multiple diagnostic kits to service different vehicle makes. Fast-forward to 1996 – The dawn of the standardized OBD-II protocols promised a new era with one universal DLC (Data Link Connector) port and code readers compatible across all makes!

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As automotive technology has progressed over the last 25 years, so have the capabilities of the OBD systems onboard our vehicles. While early systems produced basic standard codes with limited diagnostic data, modern OBD frameworks provide comprehensive health insights like freeze frame data and mode 06 test results.

The Crucial Role of OBD Codes in Vehicle Diagnostics

Like mapping our way around a new city using signposts and landmarks, OBD codes serve as the references we need to navigate the diagnostics of our vehicles.

By helping technicians pinpoint problematic components throwing specific faults, OBD codes lead us straight to the root cause of our vehicles’ suffering!

With these pivotal numeric clues generated by algorithms processing inputs from an array of onboard sensors, it would be easier to troubleshoot electrical bugs or decipher cryptic mechanical issues in our rides.

So embrace the interconnected complexity of your vehicle’s many intertwined systems with OBD codes as your guide! When dealt the next puzzling “check engine” warning, let diagnostic insights generated by your car lead the way to targeted troubleshooting and simplified repairs.

Debunking Common Myths Surrounding OBD Codes

Given the technical complexity surrounding OBD systems, misconceptions abound! We’ll tackle some common myths:

Myth: A stored code means a current issue that necessitates immediate repairs.

Truth: Codes can persist long after the problem is fixed. They alert of a “past,” not a “present” problem.

Myth – Erasing codes eliminates existing problems

Truth – The ECM will recreate codes for current faults

Myth – Upstream O2 sensor codes always indicate a failed O2 unit

Truth – They often reflect issues like vacuum leaks/exhaust leaks/wrong fuel pressure

We’ll unravel more misconceptions surrounding repairs, emissions tests, and scopes of influence through the article!

Understanding OBD Codes

Let’s build a solid base by getting to know these diagnostic messengers better!

Definition and Purpose of OBD Codes

OBD codes are alphanumeric identifiers assigned to specific vehicle fault conditions that trigger the check engine light (CEL). The numbered “signposts” are generated by algorithms processing sensor data and flagging detected malfunctions.

Types and Significance of OBD Codes

There are 3 kinds of codes:

  1. Generic/universal codes cover issues arising from engine, transmission, and emissions systems.
  2. Manufacturer-specific codes track other vehicle components like airbags and ABS.
  3. Pending/historical codes record intermittent faults.

Each code points to a unique malfunction documented within a DTC database. Techs reference this vast catalog mapping code to causes as their diagnostic cheat sheet!

OBD Codes vs. Check Engine Light

The MIL (Malfunction Indicator Lamp) is like the gateway red flag warning drivers of issues detected. OBD codes are the specific numbered clues revealing what’s behind the CEL!

Common Misconceptions about OBD Codes

Wrong assumption – All codes mandate urgent repairs.

Truth – Some don’t reflect current faults, and certain codes may not need immediate solutions!

Preventative Measures for Reducing OBD Codes

Proper maintenance is key to check engine light prevention! Follow factory service schedules, perform fluid changes regularly, and address minor issues promptly to maintain your ride’s health.

How to Read OBD Codes

Let’s learn to extract these digital messengers to derive vehicular insights!

Tools Needed for Reading OBD Codes

Code readers, Bluetooth adapters, or OBD scanners plugged into the DLC port under the dash read codes. Multifunction scanners offering broader capabilities identify codes and also analyze sensor data.

Step-by-Step Guide to Reading OBD Codes

Locate DLC Port:

Locate your vehicle’s DLC (Data Link Connector) socket. This is usually found under the dashboard on the driver’s side, often below the steering column. It may have a cover labeled “DIAG” or a standardized OBD-II logo.

Obtain OBD2 Scanner

Obtain an OBD2 code reader or scanner. Many affordable basic code readers connecting to the DLC port can read and clear generic OBD codes. More advanced professional-grade OBD2 scanners are also available and provide enhanced capabilities.

Turn Ignition to “ON” Position

Turn the ignition to the “ON” position, but do not start the engine. The engine must be off to retrieve some emission-related vehicle diagnostic information, as the ECM enters different operating modes when running.

Connect Scanner to DLC Port

Connect your Onboard Diagnostics code scanner or code reader device to the vehicle’s DLC socket using the cable provided. Make sure it clicks securely into the port. Most standard OBD-II code scanner plugs are designed only to fit one way.

Select “Read Codes” Function

Navigate to the “Read Codes” function on your diagnostic scan tool and hit enter or press the designated button to initiate the code request sequence.

Scanner Retrieves Codes

The scanner sends requests over the vehicle data bus through the port to pull any Diagnostic Trouble Codes (DTCs) logged and stored in the Engine Control Module’s (ECM) memory. The ECM responds with any set codes.

View Codes on Scanner

Available codes stored in the ECM will be displayed on your scanner’s screen. Take note of any Codes prefixed with Pxxxx, Bxxxx, Cxxxx, or Uxxxx on the scan tool readout. “P” codes relate to Powertrain issues, “B” is for Body, “C” is for Chassis, and “U” refers to Network communication codes.

Document Codes

Using pen and paper, document the specific codes retrieved from the vehicle computer for further diagnosis reference. Include the prefix and 4-digit code shown on the scanner.

Refer to Code Reference

Refer to a vehicle diagnostic code reference to identify the meaning of each code observed to gain insight into vehicle issues.

Troubleshoot and Repair

Follow troubleshooting and repair procedures before clearing codes to prevent them from being set again after deletion.

Interpreting and Understanding Code Formats

Codes follow a common XYZ structure – X signifies the system where the fault arose, while Y and Z provide specifics.

For Example – P0101 – Breaking this down

P – Indicates a Powertrain issue

01 – Points to the Mass Air Flow sensor

01- A factory-designated code for that specific component

Troubleshooting Using OBD Codes

Armed with the ID details within each code, we can strategize appropriate solutions – confirming the flagged fault and probing the relevant sensors. Code insights coupled with freeze frame data hugely assist troubleshooting!

Pro Tips for Efficient OBD Code Reading

  • Carefully document the code sequences logged, including Pending and Permanent status.
  • Note conditions when issues occur to aid diagnostics
  • Verify scanner battery charge and connections to retrieve error-free data

Clearing Non-Permanent OBD Codes

Let’s reset those resolvable DTCs now that we’ve finished troubleshooting and repairs!

Reasons and Importance of Clearing OBD Codes

Codes stay logged even after issues are addressed. Clearing them indicates to the PCM that faults tied to those codes no longer exist. Think of it as closing resolved “service tickets.”

Tools Required for Clearing OBD Codes

Code readers, scanners, or tuners can be utilized to clear non-permanent DTCs

Risks Associated with Clearing OBD Codes

Erasing codes before correcting accompanying problems will only result in the computer instantly re-logging them.

Steps for Clearing OBD Codes

Connect the scanner to the DLC port with ignition and turn the engine off. Navigate to the Clear Codes menu. Select the option to erase codes and confirm when prompted.

Unplug the tool and start the engine to verify codes do not return right away, indicating an unfixed issue.

Alternatives to Clearing Non-Permanent OBD Codes

Disconnect battery cables for 30 minutes to clear ECU memory, including stored codes. Check for persisting codes that return upon reconnecting, which indicate unresolved problems.

Clearing Permanent OBD Codes

Now, let’s cautiously erase those stubborn permanent codes.

Understanding the Concept of Permanent OBD Codes

Permanent DTCs indicate significant faults that the ECM will forever memorialize in its long-term memory storage until manually erased. They survive battery disconnects and demand special tools like a pro-level scanner to clear them.

Risks Involved in Erasing Permanent OBD Codes

Erasing permanent codes without fixing the accompanying engine issues can cause the computer to re-log them immediately. This masking tactic will only worsen existing problems by hiding the true extent of damaged components!

Tools of Erasure: What You Need to Erase Permanent OBD Codes

An advanced OEM-level scanner with special functions to delete permanent codes is required. Such professional factory tools send specific signals to unlock erased permanent codes from the computer’s memory vaults.

Step-by-Step Purge: A Guide on How to Erase Permanent OBD Codes

Connect Scanner:

    • Plug the scanner into the vehicle’s OBD II port (usually under the dashboard).
    • Turn the vehicle’s ignition to the “ON” position (without starting the engine).

Access Menu:

    • Navigate to the “Reset Functions” or “Clear Codes” menu on the scanner.

Select Custom Routine:

    • Choose the option designed explicitly for erasing permanent codes. It might be labeled as “Enhanced Erase,” “PDTC Erase,” or similar.

Initiate Sequence:

    • The scanner will communicate with the vehicle’s computer, sending a specialized command sequence to unlock secured memory sectors.
    • This process typically involves multiple steps and might require confirmation from the user.

Confirm Erasure:

    • Once the process is complete, the scanner will display a confirmation message indicating the successful erasure of permanent codes.

Options Beyond Erasing Permanent OBD Codes

Rather than just erasing permanent DTCs, prioritize properly diagnosing and fixing the severe underlying problems throwing these codes in the first place.

Permanent codes like P0301 (cylinder 1 misfire) can reflect extensive issues like mechanical timing chain abnormalities or cam/crank sensor malfunctions needing urgent repair.

Masking such critical flags with a code clear can enable further internal damage. Instead, leverage the vital clues that permanent codes highlight to eliminate major problems early!

Common OBD Codes and Their Meanings

Let’s examine some familiar frequent flyer codes vehicle owners often encounter.

Understanding OBD Code Definitions

Mapping the thousands of Onboard Diagnostics codes feels intimidating initially! However, the alphanumeric sequences reveal useful contextual clues on origin once we decode them.

For example, P0301 on General Motors vehicles indicates a misfiring cylinder 1 in the engine. Based on this revealed code definition, we can strategize logical troubleshooting steps around spark plugs, fuel injectors, etc.

On-board Diagnostic Trouble Codes Meanings

OBD 2 codes are categorized into four main groups, each represented by the first character in the code.


Powertrain codes primarily relate to engine and transmission issues. Common examples include:

  • P0300: Random/Multiple Cylinder Misfire Detected
  • P0420: Catalyst System Efficiency Below Threshold


Chassis codes relate to non-powertrain mechanical issues such as steering, braking, and suspension.

  • C0035: Left Rear Wheel Speed Sensor Circuit
  • C1214: Brake Control Relay Contact Circuit Open


Body codes involve problems with various interior and exterior components. Some examples include:

  • B0020: Front Passenger Side Deployment Loop Resistance High
  • B1000: Electronic Frontal Sensor Data


Network codes indicate communication issues between different vehicle systems. Most of these are manufacturer-specific. Common examples include:

  • U0073: Control Module Communication Bus A Off
  • U0140: Lost Communication with Body Control Module


Understanding common OBD 2 codes can be valuable for car owners and mechanics. With the right knowledge, diagnosing and fixing many issues with your vehicle without needing expensive trips to the repair shop is possible.

That being said, the list of OBD 2 codes can be quite extensive, so it is important to have a reliable resource that provides comprehensive information on each code. This list includes common OBD 2 codes and their descriptions so you can quickly identify the problem and take appropriate action.

Whether you’re a seasoned mechanic or a car owner looking to understand your vehicle better, this list of OBD 2 codes and their descriptions can help you make informed decisions about maintaining and repairing your car.

For the Complete OBD CODES List In PDF, Click Here: OBD CODES PDF LIST

POWERTRAIN On-board Diagnostic Trouble Codes

P0300 – Random/Multiple Cylinder Misfire Detected

P0420 – Catalyst System Efficiency Below Threshold

P0171 – System Too Lean (Bank 1)

P0128 – Coolant Temperature Below Thermostat Regulating Temperature

P0442 – Evaporative Emission Control System Leak Detected (Small Leak)

CHASSIS On-board Diagnostic Trouble Codes

C0035 – Left Rear Wheel Speed Sensor Circuit

C1214 – Brake Control Relay Contact Circuit Open

C0036 – Right Front Wheel Speed Sensor Circuit

C0561 – ABS Brake Control Module System

C1210 – Brake Fluid Pressure Sensor Circuit

BODY On-board Diagnostic Trouble Codes

B0020 – Front Passenger Side Deployment Loop Resistance High

B1000 – Electronic Frontal Sensor Data

B1200 – Climate Control Push Button Circuit Open

B1325 – Oil Pressure Sensor Circuit

B1422 – Seat Belt Pretensioner Deployment Control Circuit

NETWORK On-board Diagnostic Trouble Codes

U0100 – Lost Communication with ECM/PCM A

U0121 – Lost Communication with Anti-lock Brake System (ABS) Control Module

U0073 – Control Module Communication Bus A Off

U0140 – Lost Communication with Body Control Module

U0401 – Invalid Data Received from Engine Control Module (ECM)

Causes, Diagnosis, and Fixes for Common OBD Codes

P0420 (Catalyst Efficiency Below Threshold) has varied roots – a failing cat converter is just one possibility! We must gather supportive data by analyzing fuel trims, spark plugs, exhaust backpressure, and oxygen sensor outputs to pinpoint the true culprit.

Are you experiencing engine problems or poor fuel economy? It might be time to check your O2 sensors! How to detect bad O2 sensors and provide you with useful tips and tricks to diagnose and fix them.

Preventative Measures to Avoid Common OBD Codes

Catching minor issues early is key to averting many common codes. Listen for exhaust noises indicating leaks, monitor hard starts pointing to weak fuel pressure or failing sensors, and watch for misfires signaling worn plugs/wire issues to improve your vehicle’s health majorly!

Advanced Onboard Diagnostics Code Diagnostic Techniques

Leveraging Live Data for OBD Code Diagnosis

We can amplify the value of codes by pairing them with parameters like fuel trims, sensor outputs, and timing data to nail down emerging issues early through code analysis instead of waiting for a MIL light!

Freeze Frame Data and Its Diagnostic Significance

This special snapshot of sensor measurements when a DTC is triggered gives tremendous perspective into the operating scenario. Analysis of parameters like fuel status, RPM, temperatures, etc., captured in the freeze frame delivers insightful clues to trace code culprits.

Utilizing OBD Code Databases and Resources

Online repositories like that reveal the DNA behind codes are invaluable diagnostic sidekicks for both pro techs and savvy owners when interfacing with cryptic codes.

Troubleshooting Specific Systems with OBD Codes

We can strategize targeted diagnostic routines when codes indicate broad system faults – such as testing multiple components in the EVAP network when P0440 (Evaporative Emissions issue) appears.

Want to know more about EVAP leaks and how to diagnose them? Understanding this common car issue can help you save money on repairs and keep your vehicle running smoothly.

Tips for Efficient and Effective OBD Code Diagnosis

  • Note test drive observations when issues manifest
  • Record freeze frame details
  • Compare pending vs permanent code timestamps
  • Learn the technical context behind each code to support troubleshooting efforts.

OBD Codes for Specific Vehicles

Let’s highlight unique OBD elements across popular models.

OBD Codes for Ford, GM, Toyota, European, and Hybrid Vehicles

While GM utilizes expanded P and C chassis codes, BMW codes often start with DTCs like 5DF23 identifying faults within sub-controllers.

Toyota/Lexus models append specific number codes to pinpoint faults as granularly as an injector issue on a particular cylinder!

Variations in OBD Codes for Different Vehicle Types

Diesel truck DTCs focus heavily on emissions equipment-related codes. Hybrid cars incorporate motor control and high-voltage battery pack codes into their specialized vocabulary of OBD definitions.

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Tailoring OBD Code Solutions to Specific Vehicles

Troubleshooting tactics must align with an automaker’s unique OBD framework nuances – for example, scanner battery voltage verifications needed on Jeeps to confirm data reliability before code-clearing routines.

OBD Codes and Emissions Testing

Let’s explore the correlation between DTCs and smog tests.

The Impact of OBD Codes on Emissions Testing

Since OBD II monitors readiness and detects emission equipment faults, unresolved engine codes can lead to instant test failures.

Strategies to Pass Emissions Testing with OBD Codes

Erasing codes right before inspection often backfires with monitors not set to ready status. Instead, properly fix flagged issues so previously stored codes clear automatically along with restored monitor drive cycles.

Correlation between OBD Codes, Fuel Economy, and Vehicle Performance

The same O2 efficiency issues throwing P0420 cats codes also create excessive fuel trims that hamper MPG. And cylinder misfires indicated by P0300 DTCs degrade acceleration. Diagnosing codes pays dividends beyond just a passed smog score!

OBD Codes and Their Relationship to Routine Vehicle Maintenance

Codes can indicate maintenance needs before worse damage occurs. For example, crank/cam sensor codes indicate impending timing belt issues. Upstream O2 sensor heater circuit DTCs reflect degradation signaling replacement needs soon.

Insights into OBD Codes and Their Role in Environmental Preservation

By triggering alerts to deteriorating emission equipment, OBD systems help significantly reduce air pollutants emitted through early detection coupled with timely repairs.

FAQs Related To Onboard Diagnostics Code

What Is an Onboard Diagnostics Code (OBD Code)?

An Onboard Diagnostics Code, or OBD code, is part of a standardized system that indicates issues within the vehicle’s systems.

How Is an Onboard Diagnostics Code Generated?

OBD or Onboard Diagnostics codes, also known as Diagnostic Trouble Codes (DTC), are generated by the vehicle’s onboard computer (ECU) when it detects a malfunction or abnormality in one of the monitored systems.

What Do Onboard Diagnostics Codes Indicate?

OBD codes, synonymous with Automotive Fault Codes or Error Codes in Vehicles, indicate specific issues or faults within a vehicle’s engine, transmission, emissions, or other systems.

Is the Onboard Diagnostics Code Universal for All Vehicles?

Yes, the format of OBD codes, including OBD-II Codes, is standardized, but the codes’ interpretation may vary among manufacturers.

How Can I Retrieve the Onboard Diagnostics Code From My Vehicle?

OBD-II codes can be retrieved using an OBD-II Code Reader or OBD-II Code Scanner, which plugs into the OBD port near the driver’s seat.

What Is the Difference Between OBD-I and OBD-II Codes?

OBD-I codes were manufacturer-specific, while OBD-II codes have been standardized across all vehicles sold in the United States since 1996.

Do All OBD Codes Trigger the Check Engine Light?

Not necessarily. Some codes may trigger the Check Engine Light, as indicated by Check Engine Light Codes, while others may only be stored in the system without immediate visual indication.

Can OBD Codes Be Cleared, and Should They Be Cleared Regularly?

The Onboard Diagnostics Codes can be cleared, but addressing the underlying issue is essential. Clearing codes without fixing the problem may lead to recurring issues. It is important to be careful when applying techniques to clear OBD codes.

How Many Types of Onboard Diagnostics Codes Are There?

OBD codes are categorized into generic (P0, P2, P3, U0, and U3) and manufacturer-specific (P1, P3, and U1) codes, with further breakdowns such as the PXXXX Series.

What Does the “P” in OBD Codes Stand For?

The “P” in OBD codes stands for Powertrain, and P-codes relate to issues within the engine and transmission.

Can OBD Codes Help Diagnose Any Vehicle Problem?

OBD codes provide a starting point for diagnosis, and tools like OBD Code Scanner Tools aid in Advanced OBD Code Analysis. However, troubleshooting OBD codes may require additional testing and inspection.

Are OBD Codes Always Accurate?

OBD-II codes accurately indicate a system fault, but Real-time OBD Code Readings should be considered alongside other diagnostics for a comprehensive understanding.

Do OBD Codes Provide Information About the Severity of an Issue?

OBD-II codes generally do not indicate the severity of a problem. Some issues may be minor, while others could lead to significant damage if not addressed promptly. Severity Levels in OBD Code Diagnosis can vary.

How Often Should I Check for Onboard Diagnostics Codes?

Regular checks, especially when the Check Engine Light is illuminated or if the vehicle shows signs of performance issues, are recommended for proactive Vehicle Maintenance and early detection of OBD System Malfunctions.

Can I Ignore the Onboard Diagnostics Code if My Vehicle Seems to Be Running Fine?

Ignoring the Onboard Diagnostics Codes is not advisable, as underlying issues may worsen. OBD Code Historical Data and Trends in the PXXXX Series can provide insights into potential issues even if the vehicle appears to be running fine.


As we have explored, Onboard Diagnostics Codes are the gateway to vital insights into our vehicle’s health and pinpointing emerging faults early. From decoding check engine lights to extracting freeze frame data to clearing stored codes and proactively scanning for pending flags, multiple tools and techniques exist to leverage OBD to the fullest.

Build comprehensive knowledge on interpreting code meanings, correlating test drive symptoms to flagged failures, and tracing origins using technical troubleshooting trees. Know when DIY repairs reach their limits, requiring professional scanner software and equipment. Strategize around emissions tests by addressing root issues so monitors reset organically pre-inspection.

And remember, while codes accurately identify failed components, they cannot fix the problems themselves. We must carefully confirm faults through multimeter verification before making part replacements. Codes combined with common-sense testing steer us swiftly to solutions.

Equipped with the diagnostic power behind those cryptic alphas-numeric messengers, we can keep our vehicles running smoothly for the long haul.

I am Nicolas, an automobile engineer with over 5 years of experience in exhaust systems and catalytic converters. I am passionate about learning and understanding how things work, and I am always looking for new ways to improve the performance and efficiency of automotive exhaust systems. Know more about me. As an Amazon Associate, we earn commission from qualifying purchases.

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