OBD2 Diagnostics and Repair Strategies


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OBD-II Diagnostics and Repair Strategies

By Mandy Concepcion, copyright 2006, 2017

In the early part of the 21st century, we find our lives intertwined with a maze of technological wonders. From cell-phones to personal computers, no human being today can escape it. Automobiles are no exception to this rule.

With the ever changing emission laws of today, the one constant in the automotive industry is that things always change and will continue to do so. OBD II was designed from the beginning to do so as well. Late model vehicle systems are much more demanding, in both the amount of technology they posses and in the knowledge necessary to repair them. This work was designed to just that, a step-by step diagnostic approach to OBD II systems. It is also written with the State Inspections in mind. This is in direct response to the increasing adoption of OBD II inspections by most States throughout the country. OBD II repair don’t have to be difficult or cumbersome and knowledge is the key to successful OBD II diagnostics and repair.


- Basics of OBD II

- What is OBD II?

- Why do we need it? The Federal Test Procedure (FTP)

- Technical aspects of OBD II. (FF, Monitors, Pending & Current Codes, The Drive Cycle, Re-setting Monitors, etc)

- The data link connector

- Diagnostic Trouble Code implementation

- Resetting Monitors

- What are Freeze Frames and how are they useful in diagnostics

- A word about misfires

- Do I need an OEM scanner or can I get by with an aftermarket scan tool?

- Generic vs. Enhanced. What's the difference? why do you need to pull-out both codes?

- The vehicle failed OBD II-State Inspection, but is passing a 5 gas emissions test. Why is it?

- Resetting fuel trims. It’s not the same procedure for every system

- The Diagnostic Executive or Task Manager. What is it?

- Bi-Directional control capabilities are revolutionizing the diagnostic process

- Diagnosing EVAP leaks. It doesn’t have to be complicated

Section 2

- Base-lining the system includes retrieving FF, codes, & monitor status

- Freeze Frames information gathering

- Monitor status flag

- Code Setting Criteria. How and why was the code set?

- Freeze Frame and Code Setting Criteria comparison

- Dividing the diagnostic process into systems and using the codes to detect system faults

- First rule of diagnostics—Know the system you’re working on

- System by System outlook

- Which Monitors are Incomplete. The need to prove each system without having to run a drive cycle by using the scanner, saving time & money

- General Idle PID Snap-Shot

Section 3


- OBD-2 Generic PID list

- OBD I and OBD II, and general PID analysis


- TEST # 1, TEST, TEST #3, TEST #4, TEST #5


Section 4

- Putting it all together.

- Principles of diagnostics

- Basic Scope Testing and Bi-Directional Control

- No-Start, General Diagnostics

- The correct decision making process to a sound repair

- Don't assume anything or get caught in a particular mind set

- Taking all the facts into account