I have a '97 with a 3.0 liter engine, auto. trans... The CEL doesn't light-up with the (key-on-no-start mode). But I know it's not the bulb because if I run the van with the gas cap off, it lights up, and throws a code.I know it's not the PCM, because I swapped it out with another one, from my other '97 van, that lights up the right way! (got three of these same year vans,sheesh!) Does the ign. switch light the CEL, or does anyone know how this works? It won't light up with just the key on? I have 388,000 miles on this van, and things are really used! Original engine and trans. -- I do get the trans. flushed every 30,000 miles or so. Friction modifier in the engine @ every oil change too. -- Thanks in advance for all replies!

 

When you turn the key to ON (not START), the ABS, CEL, airbag, etc. lights come on. If you don't start the engine, some (don't remember which) will go out. The others will go out after you start the engine, assuming there are no faults. The ABS light is usually the last to clear. That's how it work on my '97 3.0.

You are to be commended for getting 388k miles from your Aerostar. Mine is barely at 1/3 of that and I'm trying to use it up before parts get hard to find.