Service engine light on, disconnect ground, start & light is out, turn off engine, restart & light come back on

Computrs a weird..new cars r sensitive once something has occured..u often need to disconnect batt to clear. Just taken off negative or ground wire may b enuff. Taken off red or positive then it takes ten min for engine to relearn..what evr works. Next time put coolant boost anticorrosion for bettr heat management n highr gas mile

Check grounds. 3 main grounds are battery to engine, battery to body and engine to body. Sounds like yours is battery to body.

Hello Tom:

You can reset the check engine light by clearing the DTC code(s) at the ECM port using a code reader; or by disconnecting the ground (negative) battery cable from the terminal post of the battery- wait 5 minutes, then, press on the brake pedal or turn on the headlights to draw any remaining (residual) voltage current out of the electrical system.

Replace the ground cable to the battery...restart the car.

Should the check engine light come back on, the problem was not just with the gas cap, you will have to use the code reader to pull the trouble codes...and based on the code(s), you will then have to perform diagnostic troubleshooting to trace and locate the component part(s) that are triggering the events. If you suspect a particular part or several parts, you will have to test them at the component level to see if it or they are operating properly or are malfunctioning.

CAUTION: NEVER DISCONNECT THE BATTERY TERMINALS WITH THE ENGINE RUNNING. This will instantly destroy the 6-way rectifier/voltage regulator.

Check that the Generator Failure light comes on and stays on with key on and engine off. N.G., verify your connections on the back of the generator. This circuit must function or the generator will never charge the battery. If this indicator circuit is miswired (the small spade connector is disconnected, plugged into the wrong connection or otherwise nerfed) the voltage regulator open-circuits the field (rotor) windings and in turn, the generator will never charge and freewheel. Check the circuit from the connector on the back of the generator all the way to the dash, verifying the light bulb in the dash is good. My trick is to wire in a small 3 watt bulb (or a continuity light) in series with the circuit under the hood. Turn the key on to KP II and verify it lights up.

Others: Check ground from generator to engine. This is usually a large blue cable that ties off onto a bracket near the air valve. Check ground from engine to body. Check ground from battery to body to engine. Must read less than 1 ohm on your megger.

You probably have a ground issue , looking at a wiring diagram or ground distribution diagram to see if these share a commom ground point or share power from same fuse,https://www.youtube.com/watch?v=WoN1nou5t1Q&t=224s circuit with a high resistance problem . Do you know how to test automotive electrical circuits with a DMM - digital multi-meter , how to read an use a wiring diagram to pin point test spots in a circuit . Free wiring diagrams at http://www.bbbind.com/free_tsb.html . Check out these videos on voltage drop testing an basic electrical testing . This is the way to find electrical problems .
Mastering Voltage Drop Testing with Pete Meier and Jerry Truglia YouTube
Electric Testing Techniques You Need to Know

Basic Electricity for Service Techs Ohm law Current Flow Opens Shorts

good luck !

Ey sounds like you have a bad alternator so you should test to see if the alternator is still good or bad by let the engine running then pop the hood opened and disconnected the ground cable off from the battery terminal so when you do that and if the engine dies then you have bad alternator but if the engine still running after disconnect then your alternator is still good

Code 12 is normal when engine is not running and adl is to ground ... I would have a look around for broken or disconnected vacuum lines ... Another possible is a stuck idle air control motor.

Check to make sure that the grounds are good on the engine...the scanner error could be that...and does the service engine light come on when you turn the key to run position? If not, I would take a close look at the PCM.

With the key in the ignition (but not turned), press and hold the Odometer Reset Button on the right hand side of the panel. While still holding that button, turn the key (although not far enough to start the engine) and then press and hold the Minute button on the left side of the instrument pane(if pressing doesnt work try turning the knob clockwise until service light has gone off and skip the pressing)l. Release both buttons at the same time.

Disconnect the battery and reconnect.
This should clear the computer memory.
This may cure the problem.
Suspect extreme cold primary cause in transmission?
Good Luck !