FAQs: OBDII Emissions Testing

OBDII Testing

Understanding OBDII Failures


What is OBDII?
On Board Diagnostics-Second Generation (OBDII) is a computerized system on 1996 and newer model year vehicles that monitors emissions-related components and systems for proper functionality. The OBDII utilizes an on board computer to test and monitor all the emissions-related components and systems of the vehicle.


This system is so sophisticated, it can detect malfunctioning components and systems before more serious failures occur and even before the driver of the vehicle becomes aware of a problem. The OBDII enables a vehicle owner to make cost-effective repairs before more costly damage is done to the vehicle.


OBDII testing uses a scan tool that plugs into the vehicle's computer and determines that the emission system and components are working properly. The test downloads stored information from the vehicle's computer to identify emission systems or components that are not working properly.


When an emissions control malfunction is detected, a dashboard light illuminates stating "Check Engine" or "Service Engine Soon." If the OBDII system detects a problem, a corresponding diagnostic trouble code (DTC) is stored in the computer's memory. Using an OBDII scan tool, a repair technician can quickly retrieve diagnostic codes from the vehicle computer and make necessary repairs before a more serious problem develops.


What systems are checked during the OBDII test?
The On-Board Diagnostics (OBDII) emissions test for 1996 & newer vehicles consists of the following:


What are the advantages of OBDII testing?
OBDII testing is quicker than previous emissions tests. This test determines whether there is a malfunction and/or deterioration of the devices that control the exhaust-emissions level. It can lower repair costs by detecting and storing a code specific to the problem. The OBDII test should readily identify vehicle problems, thereby reducing repair time and costs. This will, in turn, contribute to lower vehicle exhaust emissions.


Reasons your vehicle may have failed the OBDII test


Transmission-related Diagnostic Trouble Code (DTC)

If your vehicle has a transmission-related Diagnostic Trouble Code (DTC), please read the important steps below and contact the Waiver Station in your area for more information.


Transmission DTC repairs can range from $1500 to $3000, although some types may be cheaper (e.g., a transmission speed sensor problem). A waiver may be issued if diagnosis shows the extent and cost of repair to be unreasonable. Contact your DPS Waiver Station to set up an appointment. Make sure to bring your repair receipt showing the cost of repairs required to correct the transmission DTC. Only diagnosis and repair estimates from a Recognized Emissions Repair Facility (RERF) or a dealership will be accepted to qualify for this type of waiver.


NOTE: A transmission problem that has been detected by the On-board Diagnostics system (OBDII) will turn on the Malfunction Indicator Lamp (MIL) and set a DTC. The problem could be caused by a number of things, including a bad torque converter clutch (TCC) or shift solenoid switch. Transmission DTC’s can cause the vehicle to exceed emissions standards. The cost of repair may exceed the $600 minimum repair cost to receive an Individual Vehicle Waiver and still may not be enough to correct this problem. The transmission must be removed from the vehicle in order to be repaired, contributing to the high cost of repair. With a transmission DTC, you may not notice a drivability problem unless the transmission slippage gets worse. Sometimes servicing the transmission (replacing fluid and filter) will take care of the problem and sometimes not. Also, you want to make sure that there are no engine-related DTC's that are keeping the MIL ON, because an engine misfire problem will set a DTC and cause transmission shifting problems. In other words, you may feel a shifting problem, when it may just be an engine misfire. The RERF or dealer will check all electrical circuits, etc. to properly pinpoint and diagnose the problem.


Remember: The transmission is part of the vehicle's power train, so a transmission problem will turn on the MIL and can cause the vehicle to exceed emissions standards.


What causes a malfunction or DTC?
The OBDII system test determines whether there is a malfunction and/or deterioration of the components that control the vehicle exhaust-emissions levels. If this occurs, a DTC, or Diagnostic Trouble Code, is set in the PCM. A failure occurs when there is a malfunction with the OBDII equipment including the on board computer and related wiring, or when an emissions related component has failed, causing the vehicle's exhaust emissions to be 1 1/2 times the allowable emissions for the vehicle, as determined by the manufacturer.