Using the 9 modes of Global OBDII in diagnostics - - Motor Age - Automotive training, certification & parts info

Using the 9 modes of Global OBDII in diagnostics

Publish date: Mar 1, 2009
By: Peter F. Meier
Source: Motor Age

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Global OBDII applies to all vehicles sold in the United States, regardless of manufacturer.

Each shop I've ever worked in, from dealer to independent, has offered Check Engine Light diagnosis as a part of its basic menu of services. Most of these shops catered to all car lines, but could only afford to stock a single, aftermarket scan tool for technicians to use. These scan tools may have had some "enhanced" ability — that is, they may have had some access to manufacturer specific information.

But thanks to on-board diagnostics (OBDII) standards, they all had access to the same information regardless of the nameplate on the car, using the Global OBDII selection on the tool's menu.

OBDII Basics

Understanding the modes in using scan tools will help you look deeper at the Powertrain Control Module (PCM).

The Engine Control Module (ECM) on an OBDII-compliant vehicle has one primary function: to keep vehicle emissions in line. It does so by controlling and monitoring any system that will have an impact on emissions. Every powertrain-related Diagnostic Trouble Code (DTC) is related to emissions in some way.

OBDII also corrected some of the problems posed by OBDI. Code format was standardized and generic code definitions established. The Data Link Connector (DLC) also was standardized. The ECM's testing ability was enhanced from just basic circuit integrity tests, adding functional and rationality testing of emissions-related systems and components.

Diagnostic information was made more standard, with common PIDs (Parameter Identification) among manufacturers instead of a smorgasbord of terms for us to learn. Other modes were added to aid technicians not privy to OE level information or scan tools in diagnosing faults discovered by the ECM. Due to the efforts of organizations like the National Automotive Service Task Force (NASTF), OE information once considered proprietary is now available to anyone. This was not the case at the time OBDII was first implemented.

All in all, there currently are nine modes available when using the Global OBDII (not to be confused with Generic OBDII) function of your aftermarket scan tool. The majority of Check Engine Light complaints I solve on a daily basis are diagnosed and repaired using just the information these nine modes can provide.

Mode 1: Monitor Status and Current Data

Mode 1 is where you will find the status of the onboard monitors. Each monitor is associated with a system or component on the car that can impact the emissions it produces. Monitors are classified as either continuous or non-continuous. The continuous monitors are the Comprehensive Component monitor, the Misfire monitor and the Fuel monitor. All the others are non-continuous.

Printing out your findings can aid sales and also promote customer confidence.

Each monitor contains a test or series of tests the ECM uses to gauge the operational health of that system or component. The monitor status screen simply tells us whether all of the tests contained within that monitor have run to completion. When checked, they should all read Ready or Complete. If the vehicle you are testing does not use a given monitor, then the message will read Not Supported or Not Available.

Any monitor that reads Not Ready or Not Complete indicates a few things. Either the codes have been cleared with a scan tool, causing the monitors to reset, or battery power has been lost to the ECM. This can be a diagnostic aid. If power was lost due to a wiring fault or ailing battery, the ECM is constantly "rebooting" and this can cause some drivability issues.

In addition to the status of the monitors, Mode 1 is home to Current Data, also called Live Data. This is the screen showing the PID information live. Unlike some OE enhanced PIDS, however, Global OBDII PIDs are ACTUAL data. A good example is the Engine Coolant Temperature (ECT) PID. Because this PID is related to fuel control, some OEMs will substitute a data value if the true ECT reading is suspect, and that is the number you will see in enhanced mode. In Global mode, though, you will see the true ECT reading, whatever it may be.

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Peter F. Meier

motorage@advanstar.com

Peter Meier is an ASE-certified Master Technician, member of iATN and full-time tech in Tampa, Fla. His experience reaches back over 30 years, and his contributions to Motor Age reflect a wide variety of experience with almost every make and model. Articles by Peter F. Meier

Got something to say about it? Post it here!

floyd smith / Dallas, TX, UNITED STATES
Posted 2009-07-28 00:14:41.0
Mr. Peter Meier: Like you, I've been in this business for many years. My dad had a shop for forty years, and from about the age of ten, helped him cleaning up the shop floor and then the tools. This was in the 50's. But even before becoming a full time mech. I also spent maybe ten years in the service station side. You know how hard that was. It took many years to get where I'm at: A.S.E certified tech. in six areas. And a master tech. because of more then 35 years in the business. But still learning something new eveyday. My question to you is: What do you think about trade-schools that try to teach people this business (eight areas) in only 12 months, that took you and I years. I'm saying that there are the few that really want to learn, but then there are those that only want to waste time. Many will not even get into the business when they finish. Also many shops will not give them a job, when they find out that they are from a trade school. I know the answer, but would like to know what you think. I've been in the management side in this career, and this is what I look for in a person that is looking to get into this business. First, don't expect to make forty or $50,000 your first year out of a mech. trade-school. I say look for it in about five/ten years. Don't say you know everthing, that you can fix anything. I will say, well it was nice talking to you, have a nice day. I would rather take someone that does not know a thing, but has a sincere heart, can ask questions when in doubt, and always be there when someone needs help in the shop. Because I have found, there will be days when you will need help someday. It could be having to do with your job, or a personal thing, who knows? I think we all need to work together if we ever want to make it in this business. Sure I love money. I'm also in it because I like to help people. that comes first. Don't try to be perfect, just always do the best you can.

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Peter F. Meier