Your vehicle's check engine light is the most visible part of a relatively complex diagnostic system. When the light illuminates, it means your car's computer is storing one or more trouble codes. These codes can help you locate the problem, but they aren't always crystal clear to non-gearheads. One common trouble code is P0172, but what does this cryptic series of characters mean for your car?
Deciphering P0172 and P0175 (System Too Rich)
Many people choose to take their vehicle to a local auto parts store for a code reading whenever the check engine light comes on. If you took this approach, the store associate might have helpfully told you that your P0172 code means your car has a rich condition. As appealing as being rich might sound, it isn't a great situation for your vehicle.
Modern vehicles maintain a careful ratio of air and fuel to achieve the best possible performance and fuel efficiency. Multiple sensors monitor the exhaust stream to determine if the balance is off in either direction. If the system has too much air, that's known as a "lean" condition. On the other hand, too much fuel indicates that your engine is running "rich."
When your car's sensors detect this excess fuel in the exhaust stream, your computer will trigger a P0172 trouble code. You may also receive a P0175 trouble code. Both error codes mean the same thing, with the only difference being the side of the engine that detected the problem. You'll often receive both error codes at the same time.
Diagnosing and Repairing a Rich Condition
Like many check engine codes, P0172/P0175 do not tell you the cause of the problem. Instead, these codes report on a symptom. A wide range of issues can result in a rich condition, so a mechanic will typically need to look at other clues to find the problem. For example, there may be additional error codes that help point in the correct direction.
It's also worth remembering that your computer relies on sensors (the O2 sensors, in this case) to monitor its operating conditions. Bad sensors result in a "garbage in, garbage out" situation. In other words, the computer can't provide good diagnostic information if its sensors are giving it lousy data. Your mechanic will therefore need to confirm that the O2 sensors aren't the real problem.
Because there are so many potential issues that can trigger these two error codes, you'll usually need to take your vehicle to a professional for further diagnosis. An experienced technician can find the true culprit without blindly replacing parts, ensuring that you fix the problem without spending money on unnecessary parts and repairs.
Contact a local auto service if you need check engine light repair.