Diagnostic fault codes never tell you what's wrong or that a part is defective. They only indicate the circuit or system that needs further diagnosis or the unacceptable operating condition. Also, there is no fault code for a plugged catalytic converter. I suspect the code was related to "catalytic converter efficiency". That means the converter is not cleaning up the exhaust gas as it passes through. If you know the exact fault code number, you can go here:
https://www.2carpros.com/trouble_codes/obd2
to see the definitions, or I can interpret them for you.
There's another problem with driving around with the Check Engine light on. The first one is that while the engine might seem to run okay, you might be able to get away with it when you know the cause is relatively minor, but how will you know when a serious problem is detected? The warning light is already on. That second or third problem that you don't know about could also be a minor one that could turn into an expensive one when it's unwittingly ignored.
The second problem is there is always a long list of conditions that must be met for a fault code to set, and one of those conditions is certain other codes are not already set. For example, the Engine Computer determines, in part, when a temperature sensor is defective because it knows when the engine has been off for at least six hours, the coolant temperature sensor and the intake air temperature sensor had better be reading the same temperature. If the air temperature sensor has set a fault code, either because of a broken wire, or it became unplugged, the computer will set the appropriate fault code, then stop using it for reference when testing other things. In this case, it may not detect a defective coolant temperature sensor because it stopped running tests on it because there's nothing reliable to measure it against. It's not until you repair the cause of the fault code that other tests resume, and that's when the second, new problem is first detected.
When the computer sees the right conditions to open the canister purge valve to bleed off the gas fumes it has stored, it tests if that vacuum circuit is working properly by the change in mixture of the exhaust gas. It expects to see it go rich when it first opens that valve. If there's a fault code already set for an oxygen sensor, it can't use its readings to see if the purge circuit is working, so it's not going to test for that or set a fault code for it.
There's well over 2,000 defects that can be detected and set fault codes. About half of them refer to things that could potentially adversely affect emissions. Those are the codes that turn on the Check Engine light. There's two ways the engine limits harmful emissions. One is the computer carefully calculates and adjusts the fuel / air mixture for lowest emissions, then the second way is the catalytic converter cleans up those emissions that are still developed. All we know is the converter is not taking care of those emissions that still occur. The computer is likely still doing the initial calculations pretty well, but you'll never know if that changes. A slightly-rich mixture can make the engine run uncommonly smoothly, but the excessive gas can wash down the cylinder walls and wash off the coating of oil that keeps the pistons moving freely. That will show up as reduced engine life that most of us would just blame on bad luck. You might only get 300,000 miles instead of 400,000 miles. Excessive gas that washes down the cylinder walls ends up in the oil where it forms sludge. That lowers the oil's ability to isolate moving parts from each other, so there's more wear, especially to the really soft metal engine bearings.
Excessive gas will also leave the engine unburned, then it gets burned in the catalytic converter. That is a common cause of overheating and melting the catalyst. That is when you get the plugged converter that affects engine performance.
It sounds like you got lucky so far in that no other problems have developed, but driving with the Check Engine light on is a risk I wouldn't want to take. The Engine Computer is designed to tell you when something is wrong. That ability is hindered when it suspends many of the tests it normally runs while you're driving.
Be aware too you can get an idea of the severity of a problem by how the Check Engine light acts. As I mentioned, about half of the fault codes don't turn the light on because the problem detected won't affect emissions. For the next step in severity, when the problem is relatively minor, the Check Engine light may turn off while you're driving if an intermittent problem stops acting up. If it's a little more severe, the light turns on when the problem occurs, then if that problem clears up temporarily, the light "latches", or remains on until you turn the ignition switch off, then restart the engine. If the problem is still more severe but it clears up for now, the light will always be on any time the engine is running. All of these examples are for intermittent problems that stop occurring periodically. The bigger percentage of defects are permanent, or constant, meaning they never clear up until they're diagnosed and repaired.
If your Check Engine light is always on, either the problem is occurring all the time, or it is a relatively serious one. The only problems that are more serious are indicated by the Check Engine light is flashing. That means you're supposed to stop the engine as quickly as safely possible because too much unburned gas is going into the exhaust system where it is going to overheat the catalytic converter.
If the fault code you have really is for "catalytic converter efficiency", that is detected with the second oxygen sensor that is behind the converter. All cars started using them with '96 models. An oxygen sensor will not do any measuring until is reaches close to 600 degrees. That can take quite a while in some cases, so almost all of them now have small electric heaters inside them, but they still do take a little time to get hot. That would suggest the converter efficiency defect should not be tested for right away, or until you've driven a few miles to get the sensors hot enough. In this case, if the Check Engine light is on right away, it would be because the defect is considered really serious as far as emissions goes.
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Thursday, May 16th, 2019 AT 5:52 PM
