FAQ : The OBDII Trouble Code and You

OBD is the On-Board Diagnostics of your vehicle’s ECU or PCM, capable of testing many different facets of your vehicle and engine to ensure maximum performance and efficiency. These set of self diagnostic tests can test everything from your powertrain to your chassis or sensor issues.

The Engine Control Module (ECM) or Powertrain Control Module (PCM) monitors the engine for  conditions that can cause an issue with your engine or vehicle. If the ECM or PCM detects a potential problem, a warning light called a “malfunction indicator light” (MIL) on the dashboard is illuminated to alert the driver of a problem. This light is usually identified by the words “Check Engine,” “Service Engine Soon,” or the word “Check” along with an engine symbol.

If you haven’t already, check out our DTC Doctor to see our listings on the many different DTC codes that can exist and how to fix your OBDII Trouble Code.

For many people driving their car and seeing the ever dreaded “check engine soon” light can bring a sense of fear or confusion. What is wrong with my car? What does this OBDII code mean? What can I do to fix my car? My car runs rough after my check engine light or OBDII Trouble Code? How do I get out of limp mode and how can I turn off the OBDII Trouble Code light?

Q: How do I check my OBDI trouble code?

A : You must obtain a OBDII scanner or reader, and use it to retrieve the trouble codes stored in your PCM. This tool can be rented at many places and some shops will even scan and pull your codes for free.

Q: What does this 5 digit code mean?

A: The standard OBDII trouble code is usually comprised of a alphanumeric 5 digit code that reveals just what the issue with your car is. 

Here are a few sample DTC writeups on how to resolve your OBDI trouble code

• DTC P0420 – Catalyst below threshold
• DTC P0107 – MAP Sensor Overrun
• DTC P0123 – How to Service your TPS
• DTC P0127 – How to Replace your IAT
• DTC P0335 – How to Service your Crank Position Sensor

Let’s take a look at the nomenclature of the OBDII DTC Trouble Code, and how you can decipher just what these numbers and letters mean exactly.

The first letter designates what system the trouble code is referring to, such as

P = Powertrain B = Body C = Chassis U = Undefined

The second digit of the OBDII code identifies whether or not the code is a generic code or if it’s manufacturer specific depending on application .

0 = Generic 1 = Enhanced (manufacturer specific depending on application)

The third digit of the OBDII trouble code tells you what type of subsystem is being affected by the problem in your car.

• 1 = Emission Management (Fuel or Air)
• 2 = Injector Circuit (Fuel or Air)
• 3 = Ignition or Misfire
• 4 = Emission Control
• 5 = Vehicle Speed & Idle Control
• 6 = Computer & Output Circuit
• 7 = Transmission
• 8 = Transmission
• 9 = SAE Reserved
• 0 = SAE Reserved

The fourth and fifth digits inform you of what exactly the problem is in your vehicle, whether it’s a damaged sensor or the wrong sensor range for your ECU.

Q: How can I tell if my OBDII Trouble Code check engine light is on?

A : When you turn the key to the “ON” position, your check engine light should briefly light up meaning it’s ready to conduct it’s tests. After a few seconds this light should turn off, if it remains on, it’s found an issue in the car and wants to bring it to your attention. Take your vehicle to get scanned or take it to a professional mechanic who is experienced with your vehicle.

Q: My car runs bad and I think it’s in limp mode, how do I get rid of limp mode?

A: You will have to resolve the issue that is causing your ECU to force your vehicle into limp mode. While you are not doing any damage by driving the car, it’s meant as a means to ‘limp’ your car to a local mechanic.

When scanning for codes, remember that OBD II codes are stored according to priority and thus higher priority codes will be stored first. Trouble codes that are not a high priority may only set after two or three faults have been detected. Depending on your scanner, these may or may not appear to be pending DTC trouble codes.

Need the best price on a OBDII scan tool? Have any more questions about your DTC OBDII Trouble Code? Have a trouble code you would like us to tackle? Leave us a comment and let us know!