is it normal for an engine light that’s been reset after service to come back on?

after replacing an oxygen sensor-upstream- by your company mechanic on my car and he reset my engine light code. it stayed off when i drove home, but when i started the car up this morning, the engine light came back on and has stayed on. is this normal?

My car has 169000 miles.
My car has an automatic transmission.

Experienced mechanics share their insights in answering this question :
Any given diagnostic trouble code will typically have multiple faults listed as potential causes of "the" code setting. It is possible for one fault (in your case an oxygen sensor that might not be putting out the expected waveform) to be addressed in a repair and yet additional faults exist where, again, the "additional" faults are related to the original code that was downloaded. However, it is also possible that the check engine light (CEL) has come on for a new reason (a new fault) that is completely unrelated to the code that involved the oxygen sensor. There are literally thousands of diagnostic trouble codes on modern vehicles, representing countless vehicle functions, that could cause the check engine light to come on. The only way to determine whether the CEL is presently illuminated because of a new or the "old" code is to have the codes read again. To do that, please request a check engine light diagnostic and, in the context of that you could request that the original mechanic come back as he will of course be most familiar with all of the circumstances. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

How to Identify and Fix Common car Problems ?

Our sources include academic articles, blog posts, and personal essays from experienced mechanics :

In most cases, successfully repairing the issue that caused your light to come on will cause the check engine light to turn off automatically—but only after 10 to 20 “cycles”.
When you reset your computer`s memory, the warning light will turn off. However, if there`s a problem, the light will come back on as soon as the computer runs the test that caused the light in the first place.
The Light Stays On

You may think that there is still a problem with the car after the repair, but it`s because the light needs time to reset. The car`s internal computer only resets after a set period where it checks all of its sensors once more. The reset can happen automatically after around 10 to 20 cycles.

Disconnect both O2 sensors (front and rear). Start the engine and allow the vehicle to idle. After faults have stored: Cycle the ignition OFF/ON 2 times with a 10 second pause in between key cycles.
If the mechanic completed the O2 sensor replacement, reset the codes and the error code was triggered again, it is possible that the catalytic converter is damaged and needs to be replaced.
Yes. While the damage may seem small initially, the longer you drive with a bad oxygen sensor, the worse the damage will become. Eventually, you may experience rough idling, poor acceleration, engine misfires, an illuminated check engine light, and failed emission tests.
The emissions/exhaust system is the most likely culprit for many check engine lights being illuminated. There could be an exhaust leak or a problem with the catalytic converter. The mass airflow sensor (MAF) is another sensor that is easily tripped or can fail.
We rarely tell our customers what to do here at Stringer Auto Repair, but when it comes to resetting your check engine light yourself, you can really damage your automobile if you do so. It`s important to have a diagnostic check performed on your automobile if the check engine warning comes on.
A properly functioning oxygen sensor will show a rapidly fluctuating output voltage between approximately 0.1 and 1.0 volts. The time taken for the voltage to change from 0.1 V to 1.0 V (referred to as the lean to rich response time) should be about 300 milliseconds.
Do I need to replace all of the sensors at once? It is best to replace O2 sensors in pairs. For example, if you replace the downstream left sensor, you should also replace the downstream right.
Yes, a bad spark plug can confuse your car`s internal computer and trigger the O2 sensor code.
If you`re ever riding on the highway and smell something harsh from your car, that could be a quick sign that your O2 sensor is failing. If you ever begin to pick up on some changes like bad powertrain performance, engine misfires, or loud noises, that could be a symptom of your O2 sensor probably having issues.
A check engine light on your dashboard can actually come on when there is nothing mechanically wrong with your car and can simply be a false alarm. Most cars made after 2000 have an array of sensors that monitor certain systems and they simply send out a signal that everything is fine.
These problems can range from faults within the electrical system, the engine, fluid levels or to problems within the car`s emissions system. The problem can even be as simple as forgetting to tighten your gas cap – in fact, this is the most common reason why check engine lights appear in the first place.
A steady check engine light indicates a non-emergency issue, such as a loose gas cap. Flashing check engine lights warn of severe situations requiring immediate attention. Standardized diagnostic codes help identify the trouble.
Can you drive a car with the engine light on? It`s okay to drive for a few miles, but be sure to schedule an inspection of the engine as soon as possible. If the check engine light comes on while you`re driving, don`t panic! Pay attention and see if the car is driving any differently than normal.
The check engine light may stay on steadily or it may flash when the vehicle is accelerated. This is very serious. There is a severe failure of the emission control system that is causing the engine to misfire to the point that the catalytic converter is damaged each time the check engine light flashes.
One method to do so involves disconnecting your car battery and then reconnecting it after waiting a couple of minutes. You may need to drive a few miles after this until the light disappears.
Generally, oxygen (O2) sensors last about 30,000-to-50,000 miles if you have an older car. Newer sensors can go 100,000 miles before they need to be replaced. University Auto Repair lists six signs below that your vehicle`s oxygen sensor is dying.
While O2 sensors will have a natural lifespan, there are a few things that can cause them to fail more quickly. Contaminated or dirty fuel injectors, engines that burn oil, and even a very dirty air filter can cause O2 sensors to become faulty.
In most vehicles, replacing an oxygen sensor is a simple procedure that requires only a few tools. However, if this is not a task you are comfortable doing on your own, this is something that any professional technician, such as one from YourMechanic, can take care of quickly and easily.
If you remove the oxygen sensors from your vehicle, you will ruin the efficiency of the engine, thus consuming around 10 to 20 percent more gas than otherwise required, and also cause early failure of many components such as the spark plugs.
DIY sensor cleaning is completely safe. As long as you do it the right way, you shouldn`t have any problems. Many photographers regularly do their own sensor cleaning without any issues.
A dirty oxygen sensor can cause your “check engine” light to come on, and can also result in your car burning through extra gasoline. If you suspect that your oxygen sensor may be dirty, you can clean it by first removing the sensor from its housing in the vehicle, and then soaking the sensor in gasoline overnight.

Relevant Questions and Answers :

the most relevant questions and answers related to your specific issue

Battery light goes on when I start car then turns off, if I rev engine light comes back until rpms go down. Abs goes comes on/off
ANSWER : Batteries can die due to faults in the charging system so ideally a suspected "faulty" battery should be load tested before a decision is made to condemn it. The only exception to this rule is if the battery is already clearly "old" (greater than 5 years) but even then once you put a new battery in, as a replacement for a "dead" battery, you have to comprehensively check out the charging system. Diagnostic Trouble Code P0460 will result in disruption of the dashboard fuel gauge’s ability to accurately report your tank’s fuel levels. The fuel gauge readings may be erratic, or read somewhere off scale. Vehicles equipped with a low fuel warning light feature may also suffer from erratic low fuel warnings in the event of a code P0460. Unless the P0460 code has been reported alongside other trouble code, all of the vehicle’s essential systems should otherwise function normally. I would recommend that you request a check engine light diagnostic to first resolve the fault causing the P0460 code to set. The check gas cap light warning light could be due a faulty gas cap and/or small leaks in the EVAP system.

While driving on freeway truck goes into a limp mode, and the check engine light, abs light, parking break light, service brake
ANSWER : It is possible that you could be having an issue with your powertrain control module. This is somewhat of a common problem on many GM vehicles. I would recommend having your vehicle inspected by the dealership to determine if the powertrain control module is functioning properly. If not, a reflash of the powertrain control module may resolve the issue but often times it must be replaced.

is it normal for an engine light that’s been reset after service to come back on?
ANSWER : Any given diagnostic trouble code will typically have multiple faults listed as potential causes of "the" code setting. It is possible for one fault (in your case an oxygen sensor that might not be putting out the expected waveform) to be addressed in a repair and yet additional faults exist where, again, the "additional" faults are related to the original code that was downloaded. However, it is also possible that the check engine light (CEL) has come on for a new reason (a new fault) that is completely unrelated to the code that involved the oxygen sensor. There are literally thousands of diagnostic trouble codes on modern vehicles, representing countless vehicle functions, that could cause the check engine light to come on. The only way to determine whether the CEL is presently illuminated because of a new or the "old" code is to have the codes read again. To do that, please request a check engine light diagnostic and, in the context of that you could request that the original mechanic come back as he will of course be most familiar with all of the circumstances. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

Traction light/reduced engine power and check engine light coming on
ANSWER : Hello. From what you describe, it would appear that your vehicle may be experiencing some sort of intermittent wiring or sensor issue. If the problem occurred again after driving over a bump, then it may be possible that a damaged or loose wire is shorting or having contact issues. A common issue that can cause stalling is a faulty crank position sensor or wiring. I would carefully examine the engine for any loose or damaged wires. If the Check Engine Light comes back on, I would recommend having the trouble codes scanned before resetting the computer.

No dash lights, back right tail light is out, no parking lights. Brake lights work though as does head lights.
ANSWER : Hi there. In many cases, when you have electrical problems like you’re describing, it’s caused by multiple electrical component failure. It’s likely that a few electrical relays are not working; especially if you have systems that utilize the same components (such as your brake light and tail lights). I would recommend having a professional mobile mechanic come to your location to complete an electrical problems inspection first, so they can pinpoint what is damaged and recommend the right repairs.

Check Engine Light comes on after starting pickup
ANSWER : Hello there, thank you for asking about your 1992 Isuzu Pickup. A professional will have the correct equipment to read OBD1 codes. Retrieving the diagnostic trouble code(s) is the first place to start when diagnosing your vehicle. Increasing RPMs changes engine load, which can in turn affect many different sensors and components, causing the Check Engine Light to illuminate. The only way to narrow down the options and find the culprit is through in person diagnosis with an OEM compatible scan tool. A certified technician from YourMechanic can retrieve the OBD codes at your home or office.

Check engine light refuses to go off after engine replaced
ANSWER : Hello there, you have a long series of issues going on with your 2013 Hyundai Sonata. If you keep getting a repeating oil light on than there is likely a fault in that system.

Since this fault has lasted after the engine was replaced it could be a oil pressure sensor, wiring harness fault, ECU fault, oil pump, oil strainer clogged, or low oil pressure.

To diagnose this issue properly you need a complete vehicle inspection to start from square one and identify the root cause of all this.

Why can’t my check engine light come on after starting the car?
ANSWER : Hi there:

It’s nearly impossible to tamper with the ECU to disable error codes without having multiple mechanical issues exist. However, it is possible that there is a communications issue from the ECU to the dashboard or other electrical monitoring systems. The best way to know for sure is to have a professional mobile mechanic complete an electrical problems inspection first.