Q&A for How to Read and Understand OBD Codes

Search the code on the internet. This can help you figure out the meaning of the code, along with possible causes and solutions.

Check under the dash on the driver's side! This is where most OBDII ports are located.

An OBD device is better known as OBDII scan tool, which helps pull codes using the OBDII port on a vehicle.

OBDII is the newest communication protocol for vehicles. The older version was OBD, which was replaced between 1994 and 1996.

Inline 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.

In 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.

A code P0446 could mean a faulty vent valve.

Ignition/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).

Usually, 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.

Fault are DTC, diagnostic trouble codes. They have their own description so that the user can understand what is the problem in the car.

This 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.

It means there is a short to voltage or ground on COP driver circuit.

No. It will read the same code once until you clear it after checking the said fault.

CAN is short for CAN bus. CAN is the low level, transport, protocol used to send messages. It's a signaling specification.

This means "Exhaust Gas Recirculation Sensor A Circuit High." Check your EGR valve. If it's old or doesn't rattle when you shake it, replace it and reset the code. If it's OK, replace the EGR Sensor.

Wheel speed tone performance. A possible causes are wheel bearing malfunction, deformation of the wheel speed detection encoder, adhesion of foreign materials on the wheel speed detection encoder, ABS-ECU malfunction, or the number of poles on the magnetic encoder for wheel speed detection (N-pole and S-pole) is changed.

The code reader can read zero codes if it was reset. Find a shop that you would trust to do the work if needed. I found one that will give me a free diagnostic reading. That is rare these days.

Older (pre-1996) cars do not support OBDII - there's nothing for your scanner to read.

P0420 indicates a problem with your catalytic converter or O2 sensor. The hesitation at 4000 RPM means you need to get your vehicle checked by a competent mechanic. The two may or may not be related.

Google is your friend. The codes are all out there on the internet - just search for your vehicle make and code, e.g. "Ford P0420".

Haynes Repair Manual for your specific vehicle should have the OBD-2 trouble codes in the Emissions and engine control system chapter.

P0171 means air fuel mixture is too lean on bank 1. Too lean either means too much air or not enough fuel. The air issue could be a vacuum leak, where air is entering the combustion chamber that is not going through the normal intake system. Check for vacuum leaks at all vacuum connections such as heater/AC duct motors, water valves, power brake booster vacuum lines, intake manifold gaskets, etc. You also need to check the vacuum lines themselves for breaks, cracks, pin holes, or swollen line at the connection point. It could also signal a bad O2 sensor (oxygen) either before or after the catalytic converter.

It's possible that the warning light won't come back on after you clear the code. Then again, if the light does come on again soon, you must conclude that you do have an issue that needs to be addressed. And if you can't handle the repair yourself, then you should take it to a shop and have it attended to.

The P0300 engine code indicates a misfiring cylinder problem in your vehicle. The misfiring happens when insufficient fuel is burned or when the spark plug gets damaged. In addition, it can damage your car's catalytic converter in extreme conditions.