CEL/SES/MIL--All these are...
CEL/SES/MIL--All these are acro-nyms for your Check Engine Light, also called the Service Engine Soon and Malfunction Indicated Lamp.
The other major change with OBD-II is the addition of a second oxygen sensor after the catalytic converter. This is to ensure the cats weren't removed and they are functioning properly and reducing harmful emissions.
The new system requires a new set of scanners to read the date and trouble codes. You must use a scanner; there are no more jumper wires and blinking check engine lights. But the good news is one scanner can read any make or model, foreign or domestic, and all OBD-II cars have the same set of trouble codes and the same 16-pin data link connector.
Scanners and Scan Tools
Because the manufacturers were required to conform to a standardized set of DTCs, it is much easier for independent repair shops and the home mechanic to fix cars, and the scan tools needed to retrieve the codes are much more affordable than they used to be. Some, called code scanners (or simply scanners), can only read and possibly erase the engine computer's stored DTCs. The more expensive scan tools will read and erase codes but can also display live data from the sensors in real time with the engine running. This is an especially helpful feature to use to verify the proper operation of sensors and diagnose driveability problems.
PID--Parameter Identification...
PID--Parameter Identification Data information. This is the sensor data you can read in real time using a scan tool.
There are many different levels to choose from, and the more expensive the scan tool, the more it does. The tools the dealership guys have access to are top-shelf and would make even the most nerdy computer geek blush. We stopped by Galpin Ford, where technician Johnny Stein plugged his IDS scanner into the DLC of a new Mustang and gave us a tour of the various PIDs of the car's data stream and how he uses them to diagnose driveability issues such as vacuum leaks, misfires, and hard starts.
One of the coolest things Stein showed us was a relative compression test he performed in less than a minute without ever leaving the driver seat. Setting up his laptop for the compression test, Stein cranked the engine for about 10 seconds. If one cylinder makes less compression than the others, the crank will turn more quickly as that piston reaches TDC. This information is displayed in graph form on his screen, and he can determine which cylinder he should test further for ring wear or valve seating issues.
DTC--Diagnostic Trouble Codes....
DTC--Diagnostic Trouble Codes. When a sensor is malfunctioning or reading data that is out of range, it triggers a code that is stored in the ECM. Certain trouble codes will turn the check engine light on.
Fixing a Problem
So if you have access to a scan tool of some sort, fixing a late-model car should be easy, right? Not necessarily, says Westech Performance Group's Ernie Mana. "Just because the computer is giving you a code for a certain sensor, don't automatically assume that the sensor is bad."
Stein agreed, saying, "Even with all this expensive computer equipment, I still have to perform all the basic checks."
So what do you do if the check engine light is on in your car? Mana described his process. "First, I'll erase the codes and start the car again." Once your ECM stores a trouble code and turns on the check engine light, it will stay on for a number of key cycles, even if the problem that triggered the code never happens again. By erasing the codes, Mana can tell if the light is indicating a hard code--a problem that happens whenever the car is running--or a soft code, indicating an intermittent or one-time problem. "Next, I drive the car to see if the code sets again. I'll read the data stream to see what the sensor data is at the time of the fault. But then I always check the basics." He says that even if the trouble code is for a specific sensor, you must step back and perform simple power and ground checks and also inspect any fuses related to that system. "People always forget to check the fuses," he tells us. "You don't want to waste your time or your customer's money replacing sensors when the fault was in the electrical circuit of that system." Once he's verified the basic stuff, Mana says he'll look up the code in a factory service manual and follow the diagnostic flow chart recommended in the book. "Sometimes, that doesn't always fix the problem, either, but it's the best place to start."