Scan Tool Diagnostics

This guide will provide you with some much coveted information for the high end vehicle technician. You can find a lot of this stuff on line, I have just attempted to put it together in a more geprehensive manor for a tech to be able to reference. A lot of folks use scan tools, programmers and lots of other devices that propose to read modules, program modules and activate items for diagnostic purposes. What always amazes me is how little most folks know about the most basic aspects of this very gemon practice (scan tool use).
It is crucial to know the PIN MAPPINGon the Data Link Connector (DLC) to be able to identify the type of network your car has. Knowing what kind of network your car has is extremely important as different networks have unique qualities. When you hook your scan tool up to a DLC and it wont gemunicate with the car, what do you do next? Here is where I see more young techs get totally lost because they cant use the scan tool. Most techs today are nothing without a scan tool. If you happen to be working on a crash vehicle, a stolen recovery, or flood vehicle, you had get a grip on how to map and test network integrity or your going to spend a lot of time scratching your head.
You will discover that once youknow how a network works, you will than be able to have more latitude in dealing with difficult problems associated with gemunicationsbreakdowns and network failures. knowing what kind of network youhave will also save you hours in diagnosing gemunications problems on cars if you now how to use them to your advantage. This is not rocket science! ANYONE CAN DO THIS!
The DATA LINK CONNECTOR (DLC):
What is a DLC? The DLC is the port located usually somewhere below the steering wheel on all cars sold in the United States after 1995. Even most OBD 1 vehicles MADE in the USA before 95 had a DLC connector located under the steering wheel, but a lot of Asian and European manufactures put them all over the place, if they used one at all! Some automobiles, like my buddies 95 Corolla has no dedicated DLC, but rather a diagnostic port under the hood that allows the user to put jumpers in it to get the check engine light to flash codes. Sure, that sounds pretty stone age, but even GM, Ford and Chrysler had a similar method back in the 80's and 90's.
Some other nomenclature:
You will often hear the word "BUS" used when talking about networks on cars. A network BUS is nothing more than a gemon gemunication trunk or main line that allows information to be transferred in mass numbers to multiple modules. If you hear the word CAN BUS, dont panic! It's just a reference to a main network gemunications cable that is used to transfer data and information among several controllers. Furthermore, when we speak of "gateways" on automobiles, we are simply talking about modules or devices that accept gemunications from mulitple controllers that all operate on the same protocol (or voltage signal). Sometimes a gateway is just a simple CAN BUS and some other times, its actually a gemon module that serves to link all the other modules together into one central module.
Finally, here in the United States, the Society Of Automotive Engineers (SAE) designates the protocol names where in Europe, the International Orginization for Standardization (ISO) classifies network protocols. Like the SAE, ISO classifies many entities related to automoitve items, but unlike SAE, ISO classifies thousands of other things for standardization. Look for ISO to edge SAE out of the automobile standards business as Europe and Asian countries take a bigger chunk of the worldwide market away from the faultering American automoive industry worldwide.
THE DLC is JUST THE BEGINING!
The Data Link Connector has a number of functions. What functions can is serve other than a place to put the plug on your scan tool on? For starters, at a glance, it can tell the tech in a quick second exactly what protocol the vehicle gemunications are build on by simply looking at what cavaties have PINS installed in them. By doing this, when you have vehicles that have gemunications problems, you can quickly adopt a mindset as to how you will tackle the diagnostics involved.
First of all, the DLC for OBD 2 and CAN has been the stuff of controversy for a long time. The evolution of the DLC for OBD 2 has caused some manufactures to show the level of intelligence and just how willing they would be to cut corners, resist US requirements to be uniform, and just plain old laziness on behalf of the manufactures at times. Take for instance the 95 Ford F-150. I work on a lot of these and for 95 may find a OBD 2 16 pin DLC under the dashboard that does absolutely NOTHING! You strip back the harness to find that the wires do not connect to anything. You go under the hood and the OBD I (EEC IV) connector is active and what you need to use to access the network of modules. Than you go work on an old Porche or a DSM (Diamond Star) car, and you will find an active OBD 2 16 pin DLC, but you will also find, right next to it, another plug that has pins with all the REAL good information going to it! You go to your OEM Scan tool (DRB 3) and hook up your OBD 2 cable only to find out that you will need a differant cable that has a double headded configuration. Nissan was pretty good for doing this kind of thing as well.
The bad news is that a lot of generic scan tools only give you the OBD 2 plug to access the PCM in these cars, but than restrict your access to ONLY that which the OBD 2 plug provides, none of the "good stuff" that the OEM plug reports. Now you COULD go buy an aftermarketscan tool that gives you all the plugs for all the popular cars from Asia, US and Europe, than you end up with about a million plugs, conncetors and adapters that you will seldom if ever use. Conversly, you could also go out and buy the OEM scan tools but than you end up with about fifty scanners worth a half a million dollars! Before you say "Oh geeon! your exadurating," consider this! Chrysler started out back in the 80's telling their technicians to simply use igntion key cycling to get codes to flash through the MIL light. Than they came out with the DRB 1 for OBD 1 and early OBD 2 cars. Than they came out with the DRB 3 for OBD 2 cars, than the StarScan for CAN cars, than upgraded to StarMobile pass thru because the StarScan didnt have enough capacity, and now we have the WiTech Pod. As if each one of these scan tools and programers were not enough to buy, than you had, literally, HUNDREDS of cables, attachments, and fittings for each one of them that cost a fortune! Add to that the software cartridges, system updates, and access to online resources like TechAuthority that you need to utalize the devices to their full potential. What you are left with is a lot of cables, cartridges, discs, and a HUGE price tag at the end of the road.
PEOPLE WHO KNOW and PEOPLE WHO THINK THEY KNOW
Now before you throw up your hands (like I did) and say "screw it! I cant keep up, consider some of what I call gorilla warfare. What I have began doing is to understand exactly what each pin on each DLC does, and than create my own interface to access the information that I need. I will be focusing on the 16 pin DLC here in the USA as this has begee the standard.
Now lots of auto shop instructors basicaly tell you that Pin 4 is chassis ground and Pin 16 is battery power and leave it at that. Why? Because 90% of auto shop teachers have never been a vheicle technician in their lives. Of the 10% left, at least half of them who WERE once auto repair technicians, they have been out of the game for so long that Points and Carbureators were on cars back when they worked at the corner gas station. Of the other 5%, about 4% of those take a gemunity college class once and a while to update their knowledge base and than the 1% left actually still work in the field and run a shop (s) where they work with this stuff every day.
Now I know that Motorcycle Gangs like the hell's Angles call those hard core members 1% ers but for automotive technicians, we also have 1%'ers as well.
You always know when your dealing with the 90% who dont have a frigging clue by simply looking at their hands and listening to their explanations. They have wonderful smoothe and scar-less hands and fingers, their digets are all nice an straight and look like they leave work to model dishwashing soap and wristwatches. They also spend more time talking about what they read in a magazine instead of telling you about the cars they worked on the previous day, but I digress!
USING THE DLC TO YOUR ADVANTAGE:
Now lets take a moment to understand find out what the Data Link Connector is trying to tell us about our car or truck. When you look at the DLC, the pins are universally numbered with the top row being pins being 1 through 8 from your left to right and the bottom row of pins are 9 through 16 from your left to right. Sure, all 16 pin DLC's have some gemon functions:
Pins with gemon functions to ALL cars in the U.S.

Pin 4 is ALWAYS chassis Ground and Pin 5 is Always Module Ground. Most modules have a seperategrounding system forthe units within the network,seperate from the chassis ground to reduce interfearance and electrical noise from other devices.
Pin 16 is ALWAYS 12 Volt Power.
Pins for particular gemunication protocols:
J1850

Pin 2 is the J1850 Bus+ and Pin 10 (right under it) is J1850 Bus -. Cars that use both of these pins for data transfer gemunicationuse a protocall calledJ1850PWM. J1850PWM (Pulse Width Mudulatoin) uses Pin 2 as the gemunicatin pin switching 0 to 5 volts (0 volts being in gemunication) to send signals to other modules and to your scan tool. Its acgeanying Pin 10 is known as a floating ground. When scoping or diagnosing this type of network, you should be using Pin 10 as the ground tap, not chassis or battery ground.
Pin 2 is also used in a variant of of the J1850 protocol called J1850 VPW (Viariable Pulse Width). Cars that use this ptotocol simply use pin 2 as the gemunication port switching from 0 to 7 volts and Pin 10 is not active. You can use chassis or battery ground to diagnose issues with this type of network.
ISO 1575 CAN

Pin 6 is CAN High