We all know that routine oil changes are important for keeping our engines running smoothly. It’s one of the most frustrating things that can happen after you’ve just changed your oil – the check engine light comes on. There are a few possible reasons why this happens but don’t worry, it’s usually not a sign of a serious problem. In this guide, I’ll discuss what causes the check engine light to come on after an oil change and how to fix it.
The most common cause of a check engine light after oil change is that the oil cap was not put back on correctly or the engine oil dipstick is not seated properly. Another possibility is that the engine oil level was low to begin with and the oil change didn’t add enough. A low oil level causes low oil pressure in the engine which may trigger the check engine light. Also, if the oil filter isn’t seated properly after an oil change, it can cause the check engine light to come on. Check engine light does not go off immediately after you fix the issue. You have to complete certain drive cycles to reset the check engine light.
If your car won’t start after oil change, you can read my guide on the causes of car not starting after oil change.
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Is It Normal For Check Engine Light To Come On After Oil Change?
It is not normal for the check engine light to come on after oil change. If the check engine light comes on after oil change, the chances are that the oil filler cap is fitted backways or too loose. This is because the oil filler cap is not able to seal the oil properly, and air will leak into the engine. It is also possible that the engine oil itself is the problem when the check engine light comes on after the oil change. If engine oil is the wrong weight or viscosity, it can cause the check engine light to come on.
What To Do When Check Engine Light Comes On?
If the check engine light is illuminated on your vehicle’s dashboard, it means that the vehicle’s onboard diagnostic system has detected a problem. When the check engine light comes on, you should stop your vehicle and scan warning codes stored in the engine’s memory using an OBD2 scan tool. It will help you identify the root cause of check engine light on the dashboard.
If you’re getting a check engine light code, it might mean that there’s something wrong with one of your vehicle’s sensors or parts. The sensors (MAF/MAP, O2, Throttle Position) monitor your car’s intake air, fuel injection, and emissions systems. If a sensor doesn’t work properly, it might show a check engine light on your dashboard.
Moreover, if the check engine light is on after the oil change, it could be due to a low level of engine oil. If your oil level is low, add oil and see if the light goes off.
Why Is Check Engine Light On After An Oil Change?
Check engine light is on after an oil change due to the following reasons:
1. MAF or MAP Sensor Is Unplugged
If you have got your engine oil refilled by the mechanic, the chances are that the mechanic has unplugged the MAF sensor to check the engine air filter or to reach the oil filler cap while changing the oil. The mechanics and car dealers have a habit of checking engine air filters while changing engine oil to make sure that the engine runs properly.
If the MAF sensor is unplugged or the engine air filter is not properly fitted, the air will leak into the engine and the MAF sensor will not be able to record it. It will disturb the ideal air-fuel ratio for efficient combustion. This will cause the check engine light to turn on.
So, you should pop the hood and make sure all wires/hoses/clamps are proper and connectors are correctly plugged.
2. Oil Filter Is Not Properly Seated
Your check engine light also comes on after changing oil if you have installed the wrong oil filter and is not seated properly.
It is a good practice to also replace the oil filter while changing the oil. The oil filter is there to remove impurities from the oil as it circulates through the engine. If the filter is clogged, it can’t do its job properly. This is why the oil filter is also replaced while changing oil.
You can’t just install any oil filter into your engine. Each engine oil filter has a certain rating based on the filter’s material design.
If the wrong oil filter is fitted after an oil change:
- It will cause oil leakage through the engine
- It will either allow too much oil to flow without filtration or restrict the oil flow which can overheat the engine. This will cause the check engine light to turn on.
So, make sure you use the oil filter recommended by the manufacturer. Furthermore, the oil filter should be properly tightened. Also, make sure to remove the old gasket/o-ring from the oil filter. The O-ring of the old oil filter is stuck to the engine block. So, make sure to remove it. If you accidentally have a double-gasket oil filter, it will blow out and excessive oil will start leaking through it. I have explained the fitting of the oil filter in my guide on 5.3L engine common oil leaks.
3. Loose Oil Dipstick
If the oil dipstick is not properly seated after an oil change, it can cause the check engine light to come on.
The oil level is usually checked through the dipstick after filling the engine with oil. The chances are that you have not fit the oil dipstick properly after checking the oil level which may cause the air to enter the engine and affect the air-fuel mixture. This air will be termed ‘unmetered air’ as the MAF sensor couldn’t record its flow and send signals to the ECU to adjust the fuel injection accordingly.
As a result, a loose oil dipstick will cause the check engine light to come on after the oil change.
Here are some tips to fit the oil dipstick while checking the engine oil level:
- Make sure the opening of the dipstick tube, where the dipstick is inserted, should be free from all debris or burrs.
- Clean the dipstick passage of all oil residue with brake cleaner on a rag to about a depth of one and a half inches.
- Evenly coat the insert end of the dipstick with RTV silicone sealant. Allow the silicone to set up for about two to three hours before starting the engine.
- Avoid bending the dipstick while inserting it. You can put a dipstick in the freezer overnight and slip it right in.
- If the oil dipstick does not move all the way down, take an open-end wrench that fits the dipstick tube. Tap the wrench close to the tube on the lip to move it farther down the passage.
4. Low Oil Level Or Pressure
If you do not refill the engine with an adequate amount of engine oil, it will also turn on the check engine light along with the oil pressure or oil level light on the dashboard. You can read my guide on low oil pressure to learn more about its causes.
You should keep in mind that the oil dipstick does not touch the bottom of the oil pan. When your dipstick is bone dry, your engine still might have 1 to 2 quarts of oil left. Usually, the high/low marks on the dipstick are a quart or less apart.
You should always consult the owner’s manual while refilling the engine with oil. The engine oil should be between high and low marks on the oil dipstick.
5. Too Much Oil
If the engine is overfilled with oil, the check engine light may come on. Overfilling your engine with oil can cause a number of problems. First, it can cause the oil to foam and aerate, which reduces its ability to lubricate and cool your engine. Additionally, overfilling can cause oil to seep into your spark plug chambers, leading to misfires and decreased engine performance.
The engine is overfilled with oil if the oil level is above the high mark on the dipstick.
6. Oil Filler Cap Is Installed Incorrectly
If you have not put on the oil filler cap correctly after you change the oil, the check engine light will come on.
If the oil filler cap is not seated correctly, the unmetered air will suck into the engine which the MAF sensor will not be able to detect. As a result, the ECU (Engine Control Unit) will not be able to determine the appropriate amount of fuel to be injected into the engine cylinder. It will cause the engine to run lean (more air and less fuel), which will turn on the check engine light.
My car had the issue of a loose oil filler cap which was the cause of a check engine light. When I pulled the trouble code using the OBD2 scan tool, it displayed the P0171 code. The engine can also run lean and can have a check engine light if you start the engine without putting the oil filler cap in place.
You can ensure correct oil filler cap installation by tightening the cap to a hard stop. If the filler cap is not tightening properly, you can make it secure by wrapping the threads of the filler cap in duct tape. Also, make sure to install a new O-ring to the oil filler cap and grease it with the oil before tightening it.
7. Using the Wrong Engine Oil
Using the wrong viscosity of oil when changing the oil will also turn on the check engine light. When you use the wrong oil in your engine, it doesn’t lubricate the parts as well as it should. This can cause increased wear and tear on the engine, which can eventually lead to engine damage. Moreover, using the wrong oil can also affect the optimum oil pressure in your engine which can trigger the check engine light.
The check engine light is designed to warn you of potential engine problems, so it will come on if it detects an issue with the oil.
Engine oils have different viscosity grades, such as 5w30, 10w30, 5w20, etc. If the manufacturer recommends engine oil of 5w20 viscosity grade, and you use 5w30 instead, it could harm the engine.
You can read my guide on 10w30 vs SAE 30 engine oil to learn more.
8. PCV Hose Disconnected
In an engine, there is a Positive Crankcase Ventilation (PCV) system responsible for collecting the extra oil vapors from the crankcase and delivering them through the air intake system of the engine.
If the PCV hose is disconnected by mistake while checking an oil filter during a routine oil change, extra air will suck into the engine through PCV valve, due to which ECU will think engine is running lean and will turn on the check engine light.
Check Engine Light After Oil Change Jeep
If the check engine light is on after changing oil of your Jeep, you should pull diagnostic trouble codes that result in the illumination of the check engine light.
Here is how to read trouble codes in a Jeep Wrangler without the OBD2 scan tool:
- Insert your key into the ignition and turn it to the ‘ON’ position but do not start the engine.
- Push the key into the ignition cylinder and while holding it in, turn it to the ‘OFF’ position and then back to the ‘ON’ position (3) times straight making sure to end with it in the ‘ON’ position. It is important to keep pushing in on the key to prevent it from catching at the different positions along the way.
- If you do step #1 correctly, all your dash lights will illuminate and your odometer will show up as a series of (6) dashes. If your Jeep JK Wrangler has any logged in any DTC’s, they will be displayed soon after the dashes appear. Write down the DTC’s and check it/them against the list to find out what they mean.
- If your Jeep JK Wrangler has not logged in any DTC’s, the dashes on your odometer will be followed by the message ‘-done-’.
- Turn your key to the ‘OFF’ position and you will in fact be done.
Check Engine Light After Oil Change Toyota
Check engine light after oil change of Toyota can be caused when a knock sensor loosens. Usually, mechanics also look at the condition of an engine air filter while changing oil. During this procedure, the knock sensor gets loose quite easily as it is located right next to the filter, a little bit above it and towards the firewall a little more. So, you have to check the knock sensor and make sure it is properly tightened.
How To Reset Check Engine Light After Oil Change?
To reset the check engine light after oil change:
- Determine the cause of a check engine light and fix it
- Find OBD2 port of your engine.
- Connect OBD2 scan tool to the OBD2 port.
- Erase the trouble codes using the OBD2 reader by pressing the “scroll” button to find the erase option.
You can also reset the check engine light by disconnecting the negative terminal of the battery and reconnecting it.
When the check engine light turns off after clearing the codes, you should drive your vehicle for 20 to 30 drive cycles and see if the check engine light again comes or not. You can read my guide on how long can you drive with check engine light on.