Will the check engine light go on if I have low fluid in my front or rear differentials?

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Probably not. You have check engine light on?

 

negative, it's a base truck not a space ship. No instrumentation on the differential unless you add it.

 

The only way to assess front & rear differential, manual transmission, and transfer case oil level on a 1st gen is manually via the fill plugs.
Automatic has a dip stick in the engine bay.
Power steering has a reservoir with a cap stick in the engine bay.
Engine oil, dip stick in the engine bay.
Coolant, metered overflow tank in the engine bay.

Brake fluid, metered reservoir in the engine bay, and actually, the only fluid level which will give you a light on the dash is the brake fluid. The Brake light (parking brake light) will remain on after the parking brake is released if the brake fluid level is low.

 

Check engine light is pretty much just emissions related stuff. You can run out oil and it won’t turn on.

 

On a completely Stock Vehicle.

I have seen all sorts of weird things I have installed temperature gauges in all manor of places.

People spend money on what they think is important

 

No.

 

Check engine light? No

If the oil is too low the diff may light up right before the point of catastrophic failure but it's not guaranteed

 

And the windshield washer fluid, lol

 

If you plan on draining the diff, make sure the fill plug comes out first.

 

ah.. Darn, that was pretty comprehensive except for the washer fluid...