== == Evaporative Emission Control System Leak Detected (small leak) Many places will tell you to tighten the fuel cap as a first step. Have code cleared and see if that solves the problem. O-ring on Gas cap could also be dry rotted.
Most likely one of the hoses of the EVAP system has cracked or developed a leak. Trace the lines of the evap system using the under hood diagram looking for loose, cracked hoses and broken fittings. In my case the large hose coming from the canister ( by the fuel tank ) had split at the end and the system could not build up enough vacuum pressure.
An error code P1684 from an OBDII code reader indicates that the battery had recently been disconnected. This is normal if a new battery was installed but can indicate a connection issue or grounding problem.
Mass or Volume Air Flow Circuit Range/Performance Problem
This code is for a bank 1 sensor 1 problem, which means your oxygen sensor is either damaged or unplugged. If you car has two oxygen sensors, this code is usually for the front one.
I got this code on my corolla 99 the person who verify my car said it's a problem with the gaz valve sensor
You have a small "EVAP" leak. Start with replacing the fuel cap.
First you must determine what the fault code is. Obtain an OBDII code reader. These can be purchased from most auto parts stores, some will even run this for free. Correct the problem then using the OBDII reader erase the fault code.
Check engine is telling you something theres problem on your engine, I hope you did not mess with your timing if not then start checking with your spark plugs, distributor cap and rotor I hope these helps you. In most cases fixing the problem makes the light go out. If you have an OBDII code reader, you can use that to clear the code(s) but the light will soon come on again if the problem is still there. It doesn't have a cap and rotor and you can't adjust the ignition timing. That same OBDII reader or a shop with one will tell you what's wrong.
Trouble code P0780 means: Shift malfunction
I'm guessing you mean the check engine light. This will come on after a certain mileage to indicate there is some scheduled maintanence due. It may also come on if there is a problem somewhere. Attach an OBDII reader to the diagnostic port on the car and then look up the code at a obdII code site ( google search) to see what the problem is. Many auto parts will read your code at no charge in the hopes that they can sell you a part. Get the code and go home to look it up.
Found the problem. OBDII gave me a fault code. P1694. It was the Crankshaft Position Sensor. The sensor was shorting out which caused the gauges to not function.
Check the O2 sensor after the catalytic converter.
Have the OBDII connector scanned. The trouble code(s) will tell where the problem lies.