I need help,, I have a 2001 jeep grand cherokee 4.0, the engine lite just came on. here is a list of things i did . Checked for codes , but where not readable. Checked all fusses , but all seem good. In the last three weeks there has been a heating issue, i changed the thermostat twice but the cab heat is still minamal and the dash gage reads only 110 or so, not the 195 that it should read. Could it be the temp sending unit. Could it be a bad clutch fan , But why wont the codes read ? Please give me your input , Thank you...............