Other than fluids, what are some common reasons for the check engine light to go on?

The AC dash light in your 2020 Isuzu NPR indicates that there is an issue with the air conditioning system. This could be due to a number of reasons, such as a faulty compressor, low refrigerant levels, or a bad relay switch. It's important to have a professional technician inspect the system to diagnose and repair the issue as soon as possible.
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https://www.carparts.com/blog/what-does-the-transmission-warning-light-mean-common-causes/5 Common Reasons Why Your Check Engine Light Is On - Greg's ...
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There is only one reason why the engine check light will be switched on - that is when the engine management system records a fault that could affect the correct regulation of the exhaust emissions though that could have many possible causes.

Regarding older vehicles a common problem is the CAT reaching the end of it's life for a variety of reasons - often because the fuelling has become inaccurate due to bad injectors and various sensors becoming "tired".
Sometimes high oil consumption will be a significant factor or a defective head gasket dumping coolant into the cylinders...

No, the problem lies elsewhere.
Get a diagnostic check done to identify the fault

My Engine Check Light Is Illuminated

You will need to read the codes to determined the reason the check engine light is on.
Acura Service Codes

A: Replace Engine Oil
B: Replace Engine Oil and Filter. Inspect various systems and components

1: Rotate Tires and check tire pressure and condition
2: Replace air cleaner element, check drive belt and replace dust and pollen filter
3: Replace transmission fluid and transfer fluid (if equipped)
4: Replace spark plugs, replace timing belt (if equipped), inspect water pump, and inspect value clearance
5: Replace Engine Coolant
6: Replace rear differential fluid (if equipped)

Check your transmission fluid. This is a common transmission code. Torque converter clutch not locking up. You may or may not notice a difference in the driving. but defininately dont let the issue go without further investigation. the result in this light could cost you a transmission if you drive it too long without repair.

Hello,
The most common cause for what you have described is low transmission fluid.
The reason being, when the car has been sitting for a while, the fluid runs back down into the transmission pan.
So, at start up, there's enough fluid in the pan for the pump to work correctly, but, as the fluid is pumped back up into yhe transmission there's less fluid in the pan for the pump.

Be very careful not to overfil the transmission, this can trigger the, " check engine light ".

I hope this help you.
Thanks, Donnie

Emergency brake may not be all the way off .Also thelow leval brake fluid sensor might need attention....check the fluid in the master cylinder and if thats good ,unplug the sensor at the brake fluid resivor and see if light goes out

The most common reason for the check engine light to come on is the Oxygen Sensor. Take the car to a garage and have the engine fault codes checked.

Get the code, any time you get a check light on the dash,that won't tell you what is wrong or what to replace,just what system has a possible issue

There is no common cause or problems on any vehicles, and all their hundred of parts and several systems.

The dash lights have been on vehicles for 30 years.

did you drain the fluid, it may have lots of metal and be really gummed up causing it to over heat and burn off. Aside from that the most commonly overlooked "check engine" proplem is the O2 sensors, there should be 2 of them