Slide 1. Introduction.

            The class develops how to clear the engine fault without a diagnostic machine after a repair.

Slide 2. How to clear the engine fault light.

• Engine fault light.

            You may have repaired a fault in your car, but the dreaded yellow check engine light is still on the dashboard. Don't worry, this is common: the car's ECU- Electronic Control Unit stores the error in its memory.

            Although it is best to use an OBD2 scanner to clear the code digitally, there are manual methods for clearing the engine fault without using a machine. However, there is one important warning: never do this to hide a real fault. If the car has a mechanical problem and you turn off the engine fault indicator, the fault will reappear or, worse still, you will damage the engine.

• Why does the engine warning light stay on?.

            Modern cars operate with an on-board diagnostic system called OBD. When a sensor detects an abnormal reading related to emissions, injection, or electronics, for example, it generates an error code and turns on the engine fault warning light.

            Sometimes, even after replacing the faulty part, the ECU keeps the code in its “history” until it verifies, over several miles, that the problem has disappeared for good. This is where manual reset methods come into play.

• Methods for manually clearing the engine fault.

            Below are the three most effective ways to reset the control unit without a diagnostic machine.

1. The battery method-Hard reset.

            This is the most common method for clearing the ECU's volatile memory. By cutting the power, the computer “forgets” the temporary codes.

Ø      Using a suitable wrench, disconnect only the negative terminal.

            Safety tip: Disconnecting the negative terminal prevents accidental short circuits with the bodywork.

Ø      Wait between 15 and 30 minutes. This will allow the control unit's capacitors to discharge completely.

Ø      Reconnect the terminal and tighten it securely. When you start the engine, the light will probably have gone out.    

2. The ignition cycle method-Soft reset.

            Some manufacturers program the ECU to restart after a specific sequence of ignition key turns. It does not work on all models, but there is no harm in trying:

Ø      Insert the key into the ignition and turn it until the dashboard lights come on, without starting the engine.

Ø      Hold the key in that position for two seconds and then turn it off.

Ø      Repeat this process 3 or 4 times in a row.

Ø      Start the engine as normal and check the warning light.

3. Driving the car: Driving cycles.

            This is the most natural method. The ECU is programmed to perform “self-diagnostics” while you drive. If, after repairing the fault, you drive the car in a variety of conditions, in the city and on the highway, for between 50 and 100 kilometers, the system will detect that the parameters are correct and turn off the light automatically.

• What you should NEVER do.

            There are “tricks” circulating on Internet forums that can be dangerous for your car's electronics.

1. Do not remove fuses at random.

            Removing fuses to turn off the lights can deactivate safety systems, such as ABS or airbags, or misconfigure important vehicle modules.

2. Do not ignore a flashing light.

            If the engine fault light flashes instead of staying steady, this indicates a serious fault, usually an ignition fault that can destroy the catalytic converter. Stop the car immediately.

• Frequently Asked Questions (FAQs).
  1. Will I pass the MOT if I remove the engine fault by disconnecting the battery?.

            Be careful with this. If you clear the fault just before going to the MOT, you are likely to be rejected for “OBD not ready.” When you reset the control unit, the “diagnostic monitors” are cleared. You need to drive the car for a few days before going for inspection so that the system is ready again.

• 2. Is the engine fault deleted permanently?.

            Only if the fault is repaired. If you delete the code by disconnecting the battery, but the part is still broken, for example, a lambda probe or a dirty EGR valve, the light will come on again as soon as the car detects the error, which can happen between five minutes and fifty kilometers later.

• 3. Is it bad to drive with the engine fault light on?.

            It depends. If the light is yellow or orange and steady, the car usually goes into “protection mode” and loses power, but it will let you get to the repair shop. If the light is red or flashing, you should stop immediately to avoid further damage.

Slide 3. Thank you for your time.

            The class has developed how to clear engine faults without a diagnostic machine after a repair, see you soon.