Your check engine light just came on! And your worried sick. However, this is no reason to panic. The following instructions will show you how to troubleshoot a common check engine light issue found mainly in Toyota and Honda cars.
Step 1: Purchase a OBD 2 Bluetooth Scanner
The Bluetooth scanner runs around 15 dollars on Ebay (A typical autoshop will charge you more then 50 dollars just to perform a scan). After purchasing the scanner download the Torque (lite) app.
Step 2: Insert the Scanner Into the OBD 2 Port of Your Car.
The OBD 2 port is generally located underneath your steering wheel and above the gas pedal. After inserting the scanner turn on your Bluetooth and open the Torque app.
Step 3: Run a Diagnostic Scan
Go to settings then click "fault codes" and a diagnostic scan will be preformed.
Step 4: P0171
After the scan the fault codes will be available. The P0171 is a common fault code among Toyota (In this case a 2001 Toyota Corolla). The code means that you are running lean (i.e. too much oxygen in your exhaust). If the scanner reads another fault code you can proceed to troubleshoot your issue using other resources online if your are comfortable doing so (at the very least you will know what is wrong with you car before taking it to a shop).
Step 5: Removing the Mass Air Flow Sensor
The MAF sensor measures the amount of 02 entering the engine therefore telling the cars computer how much gasoline to inject to ensure the proper ratio. If this sensor becomes dirty the air/02 to gasoline ratio can be scewed (i.e. too lean). The sensor is located just after the air filter and before the throttle body. The MAF can be removed by unscrewing the two screws and disconnected the electronic connection.
Step 6: The MAF Sensor
This is what the sensor looks like!
Step 7: Clean the Sensor
Clean the sensor thoroughly (8-10 sprays) using CRC Mass Air Flow Sensor cleaner. After the sensor is clean and dry reinstall it and connect the electronic connection.
Step 8: Clear the Code
Cleaning the MAF should resolve the issue however the check engine light will need to be cleared. To do this open the Torque app: setting >fault codes> clear logged fault(s)>yes.
Step 9: No More Check Engine Light.
The engine code has been cleared and once the cars computer resets to current conditions (typically after 100+ miles) you will be able to determine if your troubleshooting efforts paid off. Hopefully this resolves your issue and you were able to cheaply (just the cost of the scanner and spray) fix your car!