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LATE MODEL OBD II DIAGNOSTICS
Prior to OBD II, fault detection was mostly
limited to "gross failures" within individual circuits or sensors. The
first generation systems could not detect engine misfire, how well the
catalytic converter was functioning or whether a vehicle was leaking fuel
vapors into the atmosphere. The list of trouble codes was also much shorter. OBD II changed all of that by adding the
ability to monitor these things so emission problems can be detected as
they develop.
OBD II still uses the Check Engine lamp to alert the driver when a fault occurs, and it still stores a diagnostic trouble code (or multiple codes) that correspond to specific kinds of faults, but it adds the unique ability to track problems as they develop and to capture a snapshot of what's going on when a problem occurs.
Almost any emission problem that causes hydrocarbon emissions to exceed 1.5 times the federal limit can cause the Check Engine light to come on with OBD II - even if there is no noticeable drivability problem accompanying the emission problem.
OBD II not only monitors the operation of all engine sensors and systems (fuel, ignition, EGR, evaporative emissions, etc.), it also monitors the operation of the catalytic converter and can even detect engine misfires! Anything that could possibly affect emissions is monitored by OBD II, including a loose gas cap! And any of these faults may set a diagnostic trouble code.
CRACKING TROUBLE CODES
A misfire will cause the Check Engine light to flash while the misfire is
occurring. A misfire that occurs in a given cylinder will also
set a P030X trouble code where "X" will be the number of the cylinder that is
misfiring. For example, a P0302 trouble code would tell you cylinder number two is
misfiring. But here's the important point: The trouble code does NOT tell
you why the cylinder is misfiring. You have to figure that out by
performing other diagnostic tests. The misfire that is causing the code to set may be due to
a fouled spark plug, a bad plug wire, a defective ignition coil in a DIS
system, a clogged or dead fuel injector or a loss of compression due to a
leaky exhaust valve, leaky head gasket or worn cam lobe.
OBD II monitors catalytic converter operating efficiency with a second oxygen sensor in the tailpipe behind the converter. By comparing upstream and downstream O2 sensor readings, it can determine how well the converter is doing its job. If converter efficiency drops below a certain threshold, OBD II will set a diagnostic trouble code and turn on the Check Engine light.
OBD II can detect fuel vapor leaks (evaporative emissions) in the charcoal canister, evap plumbing or fuel tank by pressurizing or pulling a vacuum on the fuel system. If the gas cap is loose or missing, it will detect it, set a diagnostic trouble code and turn on the Check Engine light.
In addition, OBD II can also generate trouble codes for various electronic transmission problems and even air conditioner failures such as a compressor failure.
To better understand OBD II, check out the OBD II Guide reference program below. It contains advanced diagnostic tips to help you know which scan tool data you need to look at to solve your problem.
Click Here for more info about the OBD II Guide Reference ProgramTWO KINDS OF TROUBLE CODES
OBD II is capable of generating two types of diagnostic trouble codes:
"Generic" trouble codes that are the same for all makes and models of vehicles
(these are required by law), and "Enhanced" or "OEM" trouble codes that are
unique to specific vehicles. Enhanced trouble codes also cover
non-emission related failures that occur outside the engine control
system. These include ABS trouble codes, HVAC trouble codes, airbag trouble codes and other body
and electrical trouble codes.
The "generic" trouble codes that are common to all vehicle manufacturers can be accessed using any basic fault code reader or scan tool that is OBD II compliant. Unfortunately, most older scan tools made before 1995 won't work on newer OBD II systems. You need a scan tool that has the proper hardware and software to read OBD II trouble codes and other diagnostic information.
A simple fault code reader that plugs into the vehicle diagnostic connector can usually be purchased at an auto parts store for under $100. A basic scan tool that can read trouble codes and additional system data (and erase codes) may sell for $100 to $400 depending on its features.
Need help choosing or using a scan tool? Click Here for Scan Tool Help
The only way to read the trouble code that is turning on your Check Engine light on a late model vehicle with OBD II is to plug a fault code reader or scan tool into the diagnostic connector. Most OBD II vehicles do not have manual "flash codes" as was the case on older vehicles. There are some exceptions (Nissan, for example, and some Dodge models). But for most applications, you either have to buy you own fault code reader or scan tool to self-diagnose your vehicle, or take your vehicle to a repair facility or auto parts store who can perform the diagnosis for you.
Money Saving Tip: Some parts stores (such as AutoZone) will do a FREE diagnosis for you. They will use a scan tool to tell you what the trouble code is -- but the code by itself doesn't always tell you which part needs to be replaced. Additional diagnostic tests are usually needed to isolate the faulty component.
Chrysler Powertrain Codes P1100 to P1399
Chrysler Powertrain Codes P1400 to P1899
Ford Powertrain Codes P1000 to P1299
Ford Powertrain Codes P1300 to P1499
Ford Powertrain Codes P1500 to P1699
Ford Powertrain Codes P1700 to P1999
GM Powertrain Codes P1000 to P1299
GM Powertrain Codes P1300 to P1499
GM Powertrain Codes P1500 to P1699
GM Powertrain Codes P1700 to P1899
Controller Area Network (CAN) Codes
