[captainmorgan11]

99 jeep tj 4.0 with auto trans. check engine came on at an idle (sitting at drive thru). hooked up my actron scanner "no codes". The key thing does not work on mine either.

Does anyone know why this light is one?

It runs good, I did just replace the cam and lifters about 500 miles ago. and this is the first time the check engine light came on.

thanks

 

[Moses2564]

Pull the negative terminal off of the battery for 15 minutes to reset the computer. If the light comes back, then you have a problem, and run your scanner again, or go to an AutoZone and they can check the codes for you for free.

 

[Jerry Bransford]

A loose gas cap is a common culprit of such check engine lights. But why your scanner isn't picking up the code indicates either the scanner isn't working, wasn't plugged into the port securely, or perhaps a misunderstanding of how to get it to work. The "key thing" doesn't work in models made '98 to 2000.

And a big welcome to JF!

 

[captainmorgan11]

A loose gas cap is a common culprit of such check engine lights. But why your scanner isn't picking up the code indicates either the scanner isn't working, wasn't plugged into the port securely, or perhaps a misunderstanding of how to get it to work. The "key thing" doesn't work in models made '98 to 2000.

And a big welcome to JF!

Thanks for the welcome.

I have used this scanner on this jeep prior to this with no problems. It goes through all the correct sequences and comes back with "no code" I can read other measurments with the scnner but no codes???

 

[KKiowaTJ]

If taking off the neg battery cable dont work, Find somebody with a DRB-III Chrysler scan too or a snap-on mentor. It will show you your entire loop, Volts, Fuel, Air/fuel, etc. You can hook it up and take it for a drive and it will tell you the current readouts along with stored ones for when you get back where to look.