Check Engine Codes with a Scan Tool
How to Read and Understand OBD Codes
You’re cruising down the road, enjoying your drive, when all of a sudden that most mysterious of indicators turns on: “Check Engine”. What does it mean? The engine is a pretty vast and intricate machine, so “checking the engine” isn’t going to produce many answers. That’s where the OBD-II code reader comes in. This little device will allow you to pinpoint where that error is coming from.
Getting the Codes
Obtain an OBD-II scan tool.You can find OBD-II scan readers at many online and auto-parts stores. If you have a Bluetooth-enabled smartphone, you can download an app to interpret the data and purchase an OBD reader that will display the codes and explanations directly on your device.
- If your car/light truck is older than 1996 you will need to purchase an OBD-I scanner which are more vehicle specific and do not use the universal OBD-II coding system. This article concentrates on the OBD-II system.
- OBD-II constantly monitors the performance of your engine and Emissions Control System. It will turn on your Check Engine Light whenever a malfunction occurs that causes the vehicle produced emissions to be greater than or equal to 150% of the Federal EPA mandated limits.
Locate the Diagnostic Link Connector (DLC) in your vehicle.This is a somewhat triangular shaped 16-pin connector that is commonly located underneath the left hand side of the dash near the steering column. If you have trouble locating the DLC, search for the location on the internet using your car’s model and year, or refer to the owner’s manual.
Insert the scan tool connector or code reader into the DLC.Turn your ignition on, but donotstart your engine. You will see the scanner begin to communicate with the onboard computers in your vehicle. Messages like "searching for protocol" and "establishing data transmission link" may appear on the scanner's screen.
- If the screen stays blank and does not light up, jiggle the connector to achieve a better contact between the scanner and DLC connector pins. Older cars in particular may have poorer connections.
- If you still aren't having any luck, be sure that your cigar lighter works. This is because the OBD-II system uses the cigar lighter circuit to provide voltage to the DLC. If the cigar lighter does not work, locate and check the appropriate fuse.
Enter in your vehicle information.On some scanners, you will need to input your VIN as well as the make and model of the vehicle. You may also need to specify the engine type. This process will vary depending on the scanner.
Find the menu.When the scanner finishes booting up, look for a menu. Select “Codes” or “Trouble Codes” to open the main Codes menu. Depending on your scanner and year of the vehicle you may be presented with a few systems such as Engine/Powertrain, Transmission, Airbag, Brakes etc. When you pick one, you will see two or more types of codes. The most common are Active codes and Pending codes.
- Active codes are live codes or malfunctions that are keeping your Check Engine Light on. Just because your Check Engine Light is off doesn't mean the code or malfunction disappeared, it just means that the code setting conditions haven't occurred for two or more operations of the vehicle.
- Pending codes mean that the OBD-II monitoring system has failed the operation of an emission control system at least once and if it fails again the Check Engine Light will be turned on and the malfunction becomes an Active code.
Understanding the Codes
Learn what the letter means.Each code will start with a letter which designates what system the code is referring to. There are several letters that you may see, though you may have to move to different menus to see them:
- P- Powertrain. This covers the engine, transmission, fuel system, ignition, emissions, and more. This is the largest set of codes.
- B- Body. This covers airbags, seat belts, power seating, and more.
- C- Chassis. These codes cover ABS, brake fluid, axles, and more.
- U- Undefined. These codes cover other aspects of the car.
Learn what the numbers mean.P0xxx, P2xxx, and P3xxx are all generic codes that apply to all makes and models. P1xxx codes are manufacturer specific, such as Honda, Ford, Toyota, etc. The second number tells you what subsystem the code refers to. For example, P07xx codes refer to the transmission.
- The last two digits are the specific problem that the code refers to. Check a code chart online for details on each specific code.
Read an example code.P0301 indicates a misfire condition on cylinder #1. The P indicates it's a powertrain code, the 0 indicates that it is a generic or universal code. The 3 means the area or subsystem is an Ignition System code.
- The 01 indicates it's a cylinder specific problem, in that there is a misfire condition in the number 1 cylinder. It could mean that the spark plug, plug wire or dedicated ignition coil are worn out or that there is a vacuum leak near the cylinder.
- A code does not tell you what component is defective; it only points to or indicates that a component, its circuit, or its wiring/vacuum control are malfunctioning. The code may be the symptom of a malfunction caused by a completely different system.
Diagnose your vehicle.The proper diagnosis of OBD-II codes takes years of training and practice. For example, a weak battery or worn out alternator can set five or more codes in systems that are perfectly normal. Before attempting repairs, understand that the codes alone will not tell you what parts need to be replaced or what repairs need to be made.
- If you are unsure of what you are doing, take your car to an ASE Certified Master Technician with the L1 Advanced Engine Performance Diagnostic certification, or you could end up wasting a lot of time and money.
Reset your Check Engine Light.If you’ve made your repairs, or simply don’t want to see your Check Engine Light for a while, you can reset it using most OBD scanners. The light will turn off until the car has been driven a certain amount of time (this varies from manufacturer to manufacturer).
- You can reset the Check Engine Light from the main menu of most scanners. It is also referred to as a CEL.
QuestionWhat is bank 1 and bank 2?Norm GlitzCommunity AnswerInline engines like most four cylinders only have bank one, no bank two. An inline 6 (rare these days) may have two banks: bank one in front, bank two in the rear. On a V6, typically bank one is the side of a V-6 engine whose connecting rod is first in line on the crankshaft. That's hard to see on most engines. The banks really refer to the primary catalytic converters and their oxygen sensors. There is an O2 sensor before the cat. That one tunes or trims the engine's fuel/air ratio to minimize polluting emissions. There is also one after the cat. This one monitors the cat's efficiency.Thanks!
QuestionWhat does OBD code PO128 mean?wikiHow ContributorCommunity AnswerIn determining the engine did not reach a "normal" temperature, it takes into account the length of time the vehicle has been running, the intake air temperature (IAT) sensor reading, the engine coolant temperature (ECT) sensor reading, and the speed of the vehicle.Thanks!
QuestionWhat does PO446 mean?wikiHow ContributorCommunity AnswerA code P0446 could mean a faulty vent valve.Thanks!
QuestionWhat do these codes mean: p0420, p0456, p0137?wikiHow ContributorCommunity AnswerUsually, p0420 is for a bad catalytic converter or front or rear O2 sensor; p0456 usually means you have an EVAP leak; and p0137 is for an O2 sensor as well.Thanks!
QuestionI get the code P0353. What does it indicate?wikiHow ContributorCommunity AnswerIt means there is a short to voltage or ground on COP driver circuit.Thanks!
QuestionWhat does Fault mean on my OBII scanner?wikiHow ContributorCommunity AnswerFault are DTC, diagnostic trouble codes. They have their own description so that the user can understand what is the problem in the car.Thanks!
QuestionI received a code off scanner P0320. What does this mean?Jessie BrooxCommunity AnswerIgnition/Distributor Engine Speed Input Circuit Malfunction. Possible causes are faulty Ignition/Distributor engine speed sensor, faulty Crankshaft Position sensor Ignition/Distributor, engine speed sensor harness is open or shorted, Ignition/Distributor engine speed sensor circuit, poor electrical connection, low battery charge, faulty Engine Control Module (ECM).Thanks!
QuestionWhat does CAN scan mean?wikiHow ContributorCommunity AnswerCAN is short for CAN bus. CAN is the low level, transport, protocol used to send messages. It's a signaling specification.Thanks!
QuestionIf the event that triggered the check engine light continues to happen, will the code appear more than once when scanned?wikiHow ContributorCommunity AnswerNo. It will read the same code once until you clear it after checking the said fault.Thanks!
QuestionWhat does code p1610 mean?wikiHow ContributorCommunity AnswerThis code is usually triggered when a not registered or damaged key is used to start the engine. When the starting operation is carried out five or more times consecutively with the same unregistered key, the system will lock.Thanks!
How do I tell what different OBD codes mean?
What does the dash message 9A5 CAP mean on my 2013 Dodge Caravan?
Under the I.M. readiness section, what does it mean when you have N/A (not applicable?) next to something like CAT or E-V-A-P? I had INC for incomplete before going through a whole driving cycle.
Is it possible to get DTC codes while vehicle is running?
What does it mean when there is a number adjacnet to the DTC code? The number may range from 1st trip up to as many as 20?
To read OBD codes for cars made after 1996, you’ll first need to purchase an OBD-II scanner and connect it to your car’s Diagnostic Link Connector, which you can find by consulting either the internet or your owner’s manual. Turn on the ignition without starting the engine to start the link, and navigate to the scanner’s code menu. If you see any “active” or “pending” codes, refer to a code chart to learn more about exactly what and where the malfunction is.
- A code reader is limited in its function to reading codes and clearing codes. They do not provide live data or tell you which diagnostic monitors have failed or completed successfully. Scan tools, which are more expensive and a bit harder to use, can read codes, provide detail about code specifics, read and display live data, and help confirm diagnoses.
- Do not think that the code tells you which part to replace. The friendly but usually untrained auto parts clerk will be happy to suggest many parts to try, but this can get very expensive and even confuse the issue.
- After repairs are performed, a proper drive cycle must be performed to clear all the readiness monitors. So, if needed, an emission test can be performed and passed.
Sources and Citations
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