Is it difficult to scan a car for Check Engine light codes?

September 19, 2016
Check engine light on the dash
Check engine light is on

We wanted to explore options for DIY "Check Engine" light repairs when our friend Mike presented us with such an opportunity. He had an issue with his Nissan. Recently he had his car serviced at a fast-lube place, but now his Check Engine light, as well as the Traction Control light came on. The car drives fine, but the engine runs a bit rough at idle. Mike wondered how bad was the problem because he planned an out-of-town trip for the weekend. It was late afternoon and the fast-lube place and his dealership were on the other end of the town, so we drove off to the nearest part store and purchased this basic OBD II scan tool for just over $50 (photo).
In Mike's Nissan Pathfinder, the OBD II diagnostic connector is located under the driver's side of the dash, above the pedals (photo). This is the most common location in most cars. There was no instructions in the scan tool package, so we downloaded from the manufacturer's website in pdf format.
As per the instructions: turn the ignition off, plug in the scan tool, then turn the ignition back on. The scan tool communicates with the vehicle's computer and shows this screen (photo). Click "Diagnose" and it displays the Monitor Status (photo). The "MIL status" indicates "ON". Malfunction Indicator Light or MIL is a technical term for the "Check Engine" light. "DTCs in this ECU: 1" which means there is one diagnostic trouble code or DTC stored in this module. Check Engine codes are stored in the Powertrain Control Module (named ECU in this scan tool) which is the main vehicle computer that controls the engine and transmission.
Click "Enter" again and the scan tool goes into the Diagnostic Menu (photo), select "Read Codes" and click "Enter." The scan tool shows the trouble code (DTC) that caused "Check Engine" light: P0101 - Mass or Volume Air Flow A Circuit Range/Performance (photo below).

Scan tool displays Check Engine light code
Scan tool displays Check Engine light code

Google search reveals that the code P0101 is often related to the Mass Airflow Sensor. Another Google search for "Mass airflow sensor location" says that this sensor is installed in the air intake of the engine, close to the air filter. So we turned the ignition off, set up the parking brake and opened the hood to take a look. There is the mass airflow sensor on top of the air filter box and what is that? The clamp on the intake boot coming from the air filter box came loose and the intake boot came off (photo). Turns out our friend Mike has been told during a recent service that his air filter was dirty and needs to be replaced. Mike later replaced the air filter himself, but forgot to tighten the intake boot clamp. We know that this could easily cause the code P0101. We re-secured the boot and tightened the clamp properly (photo). Everything looks right now. The hood is closed, the ignition is turned back on. On the scan tool, we navigated back to the Diagnostic Menu and select "Erase Codes" (photo).

2009 BMW 3-series sedan

Once it's done, as per the instructions, turn the ignition off, disconnect the scan tool. We started the engine and it was running fine. We drove the car for a few blocks and no lights on the dash. The Traction Control light wen away too.

Of course rarely "Check Engine" problems are as simple as this one, but if you know the trouble code, there is plenty of information available, including some on our website. You can look up some of the common "Check Engine" codes here. Google works very well too. If you know the trouble code, google it together with the make and model of your car, for example: 2008 Ford Escape code P0446. You might find that someone had the same problem with the same car and already posted a video or shared the repair information on some forum.

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