OBDII If your connector looks like this or you have a 96 and newer GM You have OBDII. A word on OBDII systems! You can goto most parts stores and get your codes read and sometimes they will even erase them for you too! The problem with this is OBDII is smarter that us! It knows when codes have been erased! If your light is on and you simply erase the codes and turn off the MIL you will still fail an emissions test. After codes have been cleared the vehicle must be subjected to a "drive cycle" before the PCM will provide a ready status on it's systems. If the system is 'not ready' you fail no questions asked. Also if you drive up and your light is on for any reason, you fail! I know some of you are thinking... 'I'll just yank the bulb out of the dash!'... Guess what!!!! You fail! The light must be operational. Even if the system is in perfect working order and there are no codes or failures and all sensors report ready if the MIL lamp fails to illuminate you fail. Allot of you are starting to think 'this stuff bites' or 'I think I'll just buy an old car and forget all this mess'! Believe me I understand the frustration but these systems are here to stay so if you don't want to end up shelling out the big bucks to repair shops you'll want to pay attention! The connector for OBDII is standardized and ALL 96 and newer vehicles have one with this pin configuration. These codes and plug apply to all makes and models so your Honda or Nissan will be the same. Pin location Pin output. PIN 1 Manufacturers discretion PIN 2 SAE J1850 Line (Bus +) * PIN 3 Manufacturers discretion PIN 4 Chassis Ground PIN 5 Signal Ground PIN 6 SAE J2284 (CAN High) * PIN 7 K Line of ISO 9141-2 & ISO/DIS 4230-4* PIN 8 Manufacturers discretion PIN 9 Manufacturers discretion PIN 10 SAE J1850 Line (Bus -) * PIN 11 Manufacturers discretion PIN 12 Manufacturers discretion PIN 13 Manufacturers discretion PIN 14 SAE J2284 (CAN Low) * PIN 15 L Line of ISO 9141-2 & ISO/DIS 4230-4* PIN 16 Unswitched Vehicle Battery Positive Some 1994 1/2 and 1995 GM vehicles have the 16-pin connector but have accessible OBD-I codes. Check the underhood emissions sticker to confirm, and if yours is OBD-I, the codes are accessed by bridging terminals 5 and 6. If your vehicle is OBD-II, a scan tool or computer is required to access the codes. All OBDII codes follow this principle layout. P0300 They are a 5 character format with the first being a letter and the next 4 being numbers. There are 4 different letter codes. Letter System type P Powertrain codes B body codes C chassis codes U UART/Network codes The first number determines if it is a Manufacturer code or a 'standard' OBDII code. If the first number is "0" it's a Standard code and applies to every OBDII vehicle on the road. If the number is "1" or even "2" then it's a Manufacture specific code. The second number determines the system affected. Number System affected 1 Fuel and Air metering systems. 2 Fuel and Air Metering systems, Injector specific circuits. 3 Ignition system misfire or malfunctions. 4 Auxiliary Emissions control systems (Evaporative systems) 5 Vehicle Speed monitor systems and Idle Control systems 6 Vehicle Computer output systems and circuits 7 Transmission systems 8 Transmission systems The last 2 numbers are the specific fault. There are allot of Acronyms used in OBDII systems. If I told you that you had a DPFE sensor failure you would just look at me like I was speaking another language! Here is a list of commonly referred to terms: Acronym Meaning of acronym AFC Air Flow Control ALDL Assembly Line Diagnostic Link. Former name for GM (only) Data Link Connector, the connector socket into which the scan tool plug is inserted, sometimes used to refer to any pre-OBD II computer signals CARB California Air Resources Board CFI Central Fuel Injection (a.k.a. Throttle Body Fuel Injection TBI) CMK or CRK Camshaft sensor CO Carbon Monoxide CPK Crankshaft sensor CTS Coolant temp sensor DLC Data Link Connector Driving Cycle A specific sequence of start-up, warm-up and driving tasks that tests all OBD II functions DTC Diagnostic Trouble Code ECM Engine Control Module or Electronic Control Module (the computer) ECT Engine Coolant Temperature EEC Electronic Engine Control EEPROM or E2PROM Electrically Erasable Programmable Read Only Memory EFI Electronic Fuel Injection EGR Exhaust Gas Recirculation EMR Electronic Module Retard EPA Environmental Protection Agency ESC Electronic Spark Control EST Electronic Spark Timing DPFE Differential Pressure Feedback EGR sensor (On Ford and Mazda OBDII systems) DTC Diagnostic Trouble Code FLI Fuel Level Indicator Fuel Trim Engine computer function that keeps the air/fuel mixture as close to the ideal 14.7:1 stoichiometric ratio as possible HC Hydrocarbons HEI High Energy Ignition HO2S Heated Oxygen Sensor IAT Intake Air Temperature ISO 9141 International Standards Organization OBDII communication mode, used by Chrysler and most foreign cars. One of three hardware layers defined by OBD II J1850PWM (Pulse Width Modulated) SAE-established OBD II communication standard used by Ford domestic cars and light trucks. One of three hardware layers defined by OBD II J1850VPW (Variable Pulse Width Modulated) SAE-established OBD II communication standard used by GM cars and light trucks. One of three hardware layers defined by OBD II J1962 SAE-established standard for the connector plug layout used for all OBD II scan tools J1978 SAE-established standard for OBD II scan tools J1979 SAE-established standard for diagnostic test modes J2012 SAE-established standard accepted by EPA as the standard test report language for emission tests MAF Mass Air Flow MAP Manifold Absolute Pressure MAT Manifold Air Temperature MFG Manufacturer MIL Malfunction Indicator Light. The "Check Engine" or "Service Engine Soon" light on your dash. NOx Oxides of Nitrogen O2 Chemical representation of Oxygen but more commonly used to reference the O2 sensor OBD On-Board Diagnostics OBDII or OBD II Updated On-Board Diagnostics standard effective in cars sold in the US after 1-1-96 Parameters Readings on scan tools representing functions measured by OBD II and proprietary readings PCM Powertrain Control Module, the on-board computer that controls engine and drive train PCV Positive Crankcase Ventilation PID Parameter ID Proprietary Readings Parameters shown by on-board computers which are not required by OBD II, but included by manufacturer to assist in trouble shooting specific vehicles. RPM Revolutions or Rotations Per Minute SAE Society of Automotive Engineers, professional organization that set the standards that EPA adopted for OBD and OBD II Scan Tool Computer based read-out equipment to display OBD II parameters SES "Service Engine Soon" dash light, now referred to as MIL SFI Sequential Fuel Injection Stoichiometric Ratio (Stoy'-kee-o-metric) Theoretical perfect combustion ratio of 1 part gas to 14.7 parts air TBI Throttle Body Injection TPI Tuned Port Injection TPS Throttle Position Sensor VAC Vacuum VCM Vehicle Control Module, the in-car computer that oversees engine management, transmission operation, anti-lock brakes, and other functions not directly related to emissions control VIN Vehicle Identification Number VSS Vehicle Speed Sensor WOT Wide Open Throttle So now that you know more about OBDII here are some known issues! A very common code to get is P0420 or P0421. These refer to the converter. Many times after testing these systems no issue can be found with the converters or the related HO2S sensor. This doesn't mean swap the converter or the sensor. If you have this code and you can't find any obvious problems (like a gutted/missing cat or missing or damaged sensor/wire) and the vehicle has no drivability problems, there may not be a problem!! I can already see the eyebrows going up!! There are a few reported cases where the software in the PCM has too narrow a range. These are usually noted in TSB's and typically can be performed at a local dealership at no cost to you. I can also hear 'but my warranty is out!' Most Catalysts systems have a Federally Mandated 8 year 80,000-mile warranty. This is a fact that the dealership doesn't want you to know but...if your vehicle has a P0420 or P0421 code before 80,000 miles or 8 years the dealership can be liable for replacement or repair. 99% of the time it takes a matter of minutes for this EEPROM FLASH and it turns off the MIL light immediately. Another Common issue is O2 codes. If you have a vehicle that has low or no output codes for any O2 sensor but when tested the O2 seems fine, Change the O2. I have had this problem before. A car with O2 no output codes came in but when running a 'live' scan and 10 miles worth of drive testing showed no problems. The O2 was switching within normal parameters and measured emissions were below the standard. I scratched my head on this one for a while. I would clear it and the customer would drive for days but it would always come back. Finally after a few weeks I got the car for 3 days. I must have put over 100 miles on it with the scanner when just for a few min the sensor just shut down like a windows freeze. Nothing for about 5 or 6 miles then right back to normal. When the sensor was changed the light went off and has not returned for that code again. That was 3 years ago! OHH boy the IAC and EGR codes!! GM IAC's and EGR's have a pattern failure. These are common failures before the expected or intended service interval. 99% of these failures are due to foreign debris in their pintal valves. EGR valves that seem to have no obvious signs of being faulty but continuously give EGR Low Flow codes are usually clogged passages in the valve or manifold or sticking pintal valves. There are TSB's about The EGR codes and even some EEPROM flashes for this problem. Generally cleaning these at the first sign of the problem will solve the issue. If they are let go they end up wearing the mechanisms inside and begin to stick regardless of how clean they are. IAC's are very sensitive things too. When cleaning them don't use hard brushes on the pintal and never stick anything in the throttle body orifice! Use throttle body cleaning spray instead. Also EGR flow excessive codes can sometimes be linked to a bad converter. It is possible to get EGR excessive codes and NO P0420 or P0421 codes. Since the rear HO2S only measures one of the 3 gasses produced it may not pick up the bad converter but the converter is part of the EGR system too. When you get a low/high flow it is referring to the entire system and not just the EGR valve. Unless you get a EGR specific code like EGR Pintal valve position, you can't rule out the rest of the EGR system and since some of these valves are over 300$ that can be a costly mistake!!! Cylinder misfire!! There have been issues in the past with early OBDII systems being overly sensitive to misfire. While this was mostly Ford/Mazda systems it still applies to all vehicles. If you have a cylinder misfire that just won't go away IE P0303 (cylinder 3 misfire) and you have checked every single thing you or your buddies can think of but this code just won't go away then read on! The crankshaft position sensor is what detects misfire. It detects the cranks acceleration rate. When the rate is erratic or slightly abnormal it triggers a misfire. By interpreting where the crank was in the rotation and where the camshaft was at that instant it can determine what cylinder is misfiring! When more than one cylinder is misfiring at the same time or in rapid succession it will give a random multiple cylinder misfire or P0300. In some early systems with manual transmissions and automatics (when the converter is locked) the change in crank rotations caused by going over rough roads or train tracks caused misfire codes. A TSB can usually be found on this and an EEPROM flash can be performed to fix this problem.