How to use a scanner: A comprehensive Guide

Learn how to use a scanner to fix your car and clear codes

Scanner tools, also known as OBD-II scanners, are invaluable devices for diagnosing issues in modern vehicles. Whether you’re a DIY mechanic or just want to understand your car better, knowing how to use a scanner tool can save you time and money. This guide will walk you through the basics of using a scanner tool effectively.

Understanding code readers versus scanners

Before diving into scanner usage, it’s important to understand the difference between a scanner and a code reader.

What a code reader does
• Polls the ECM and displays generic Powertrain (P) trouble codes
• Clears non-permanent trouble codes
• Displays the status of readiness monitors
• Depending on the features of the code reader, it may display the code’s definition, and display the most common causes of the code.

What a code reader does NOT do
• Most inexpensive code readers can’t read Chassis (C), Body (B), Network (U) codes. So they can’t read airbags, ABS, traction control, or stability control codes.
• Most inexpensive code readers can’t read manufacturer-specific or enhanced trouble codes
• Can’t read live data
• Can’t issue bi-directional commands

Different scanners have different capabilities

There’s no industry standard definition of a scanner tool. But in practice, scanners do everything a code reader can do; plus, they access live data from the ECM. So you can see sensor data in real time.

• The more expensive scanners have recording capabilities and a built-in library of code definitions and common fixes for each code. Some allow you to peek behind the user interface and access Mode $06 data.
• The professional versions provide bi-directional communication, allowing you to activate solenoids from the keypad.
• Many subscription-based scanners provide access to technical service bulletins and wiring diagrams,

Start by reading the trouble codes

Connect the scanner to your car’s OBDII port and start the engine. Then, read and note the trouble codes.

Next, find the definition of the codes. Here’s how trouble codes are arranged.

How to read trouble codes

An OBDII trouble code consists of a prefix and at least four numerical digits. All manufacturers have to comply with a universal code protocol. However, in order to accommodate manufacturers’ needs to communicate trouble codes specific to their make, model, or engine, there are two types of code patterns. OBDII trouble codes are either generic or enhanced. A generic OBDII trouble code is a code that’s universal and applies to all vehicles, while an enhanced code is manufacturer-specific and even make and model-specific.

All generic trouble codes start with P0 (zero, not capital O).
All enhanced trouble codes start with P1

Next, OBDII trouble codes are divided into categories based on the system involved.

1 = Emission Management (Fuel or Air)
2 = Injector Circuit (Fuel or Air)
3 = Ignition or Misfire
4 = Emission Control
5 = Vehicle Speed & Idle Control
6 = Computer & Output Circuit
7 = Transmission
8 = Transmission
9 = SAE Reserved
0 = SAE Reserved

So all P01_ _ codes relate to engine management issues
All P02 _ _ codes relate to fuel and air injectors

Other kinds of trouble codes

Manufacturers have expanded the use of trouble codes beyond emissions-related problems.

P – Powertrain codes relate to emissions issues caused by the engine and transmission. All emission codes start with P.

Each manufacturer is allowed to use their own definitions for the following codes.
B – Body codes usually refer to issues with the charging or starting systems
C – Chassis codes usually refer to brakes and stability control systems
U – Communication-bus/network codes refer to problems with the data lines that run between computer modules.

When are codes set?

Auto computers don’t set a check engine light or trouble code until certain test criteria are met. These criteria are called drive cycles. A vehicle can have dozens of drive-cycle criteria, one for each system. Each manufacturer decides when to run the test drive cycle. If the computer runs the test and it turns out good, it sets a Readiness Monitor, meaning that the system has tested good and can be inspected by an emissions test station. If a drive cycle has not completed successfully, the Readiness Monitor will not set, and the emissions testing station in your state can tell right away that your vehicle is NOT ready to be tested. That way, you can never fool an inspector by erasing trouble codes.

How to use a scanner to read live data

Higher-end scanners allow you to see the same rapid changes that the ECM is seeing. Here are some of the most important data points you can find in live data:

• Short—and Long-Term Fuel Trims—This data tells you if the ECM is adding or subtracting fuel to get to the right air/fuel mixture. Short-term fuel trims are always changing, so they’re less important than long-term fuel trims (LTFT).

Here’s an example of what fuel trims can tell you. Let’s say the LTFT is +25%. That means the ECM is seeing a lean condition in the exhaust and is adding maximum fuel to compensate. What’s causing the lean condition? You have to find out. Possible causes are a vacuum or exhaust leak that’s allowing too much unmetered air into the engine, low fuel pump pressure that’s not providing enough fuel, clogged fuel injectors, etc.

For more information on Check Engine Lights, click HERE

For more information on readiness monitors and examples of drive cycles, click HERE

For more information on oxygen sensors, click HERE

To find out which oxygen sensor the code refers to, click HERE

© 2012 Rick Muscoplat