Read and Fix Your Own Check Engine Codes

Often the first and maybe only sign that you have a MAF or mass air flow sensor malfunction or another issue with your car or truck is the dreaded check engine light. But that check engine light doesn’t mean anything without a check engine code scanner which is also called an OBD2.

How Do OBD2 Readers Work?

Let’s talk about how the OBD2 scanner works. Plug in your OBDII code scanner to your car (usually it’s a port directly under the steering wheel). It deciphers that check engine light into codes that tell you what is malfunctioning on your car. These codes are broken down into 4 categories:

B – Body
C – Chassis
U – Network Communication
P – Powertrain (Most Common)

Each of the codes that your OBDII scanner displays, should start with one of these letters which indicates the malfunctioning system. These letters are followed by 4 digits that further break down what is malfunctioning. The first digit tells you if it’s a standardized code, which means all vehicles, regardless of make, share that code. Or if it’s a manufacturer-specific code, meaning it is specific to the make of your vehicle.

0 – Standardized Code (Most Common)
1 – Manufacturer Specific Code

The second digit tells you what subsystem is malfunctioning. This ranges from 1-8 (7 and 8 both deal with transmission codes).

1 – Secondary Air Injection System
2 – Fuel System
3 – Ignition System
4 – Exhaust Monitoring System
5 – Idle Speed Control or Cruise Control
6 – Input / Output Signal from ECU
7 and 8 – Transmission System

The last two digits are a pair that breaks down the exact part or system that is malfunctioning. Here’s an example of how a common engine code tells you what’s wrong.

Code P0101 - Mass Air Flow (MAF) Circuit/Performance Malfunction

P – Powertrain (The issue is in the engine or peripheral components)
0 – Standardized Code (A standard for all makes and models)
1 – Air and Fuel Mixture Issues (Engine to air mixture is either too rich or too lean)
01 – MAF (Mass Air Flow) Sensor Malfunction (Either the sensor is bad or it detects the airflow is too high or too low)

A Little About the P0101 MAF Sensor Code

P0101 Code Explained: Mass or Volume Air Flow Circuit Range/Performance Problem

Issue Severity: IMPORTANT – Driving for an extended period with MAF issues could damage your engine.

Repair Urgency: Repair the cause of this code ASAP. Prolonged use, while this code is in effect, may damage your engine.

Diagnosis: Code P0101 will not pose an immediate danger to the driver or passengers and the vehicle will still run, although it may be a rough ride. BUT it may decrease fuel efficiency and possibly damage your engine if left unattended.

The mass airflow (MAF) sensor measures the air entering the engine. Check engine light code P0101 is set when the amount of air entering the engine, as measured by the mass air flow sensor is outside of the manufacturer’s specified range.

All You Never Wanted to Know About OBD2 Scanners

Congratulations! In this 2-minute code scanner course, we covered OBD2-101, not to be confused with OBD2 – Code P0101. You now know everything you need to know to read and decipher the codes provided by your code scanner. These scanners are not expensive at a base level and they come in all kinds of configurations including Bluetooth that you leave plugged in and get readings on your phone app. What a time to be alive!

What Happened to the OBD1?

A little trivia to impress your fellow OBD2 users: If there’s an OBD2, was there ever an OBD1? Yes!

In 1988 there was an SAE recommendation that required a way to provide a standard onboard diagnostic and a set of diagnostic codes. From this, the OBD1 was born in 1991. Its birthplace was California and it was very rudimentary compared to the OBD2. It only gave a VERY basic diagnostic location of where the issue was. Still, the OBD1 was groundbreaking because it cut down on a lot of diagnostic work that mechanics had to perform. In 1996 it was replaced by the OBD2 in most vehicles and soon all OBD1 scans and emissions testing were rendered obsolete.

Read more about P0101 MAF Sensor errors on our Code P0101 - Mass Air Flow (MAF) Circuit/Performance Malfunction blog.