Division of Air Quality - Motor Vehicle I/M Program



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Motor Vehicles >> Inspection and Maintenance (I/M) Program >> Communication Issues

Analyzer Communication Rates

In the past, there have been minor difficulties with emission inspection analyzers communicating with some vehicle's emissions computer. Not having a standard to follow, the vehicle manufacturers used a variety of communication protocols (languages) to transmit vehicle emission information to the emissions analyzers. Examples of protocols that have been used, but not limited to, are as follows; Ford vehicles use a Pulsed-Width Modulation, GM vehicles use a Variable Pulse Width Modulation, Chrysler/European/Asian vehicles use the ISO 9141 system, and other vehicle manufacturers may use Key Word Protocol. Starting in 2003, some manufacturers began using Controller Area Network (CAN), a high-speed communications protocol, in their OBDII systems. The Federal Government has seen the advantages of using the CAN protocol and has mandated that all light duty vehicles must use this form of communication in their OBD II systems by 2008. There were two variations of CAN, an earlier more widely used 11 bit version and a more recent robust 29 bit version.

Due to the fluidity and complexity of these systems, emission analyzers have to continually be modified/updated to enable successful communication with some of the newer vehicles. The following table represents recent initial vehicle communication rates for the emission analyzers, by manufacturer.

Communication Rates (Percents) Initial Inspections

Manufacturer	May 2007	June 2007	July 2007	August 2007	September 2007	October 2007
Ease Diagnostic	99.90	99.91	99.90	99.91	99.89	99.91
ESP	99.78	99.77	99.78	99.75	99.76	99.79
Snap-On	99.79	99.79	99.78	99.89	99.74	99.77
SPX	99.91	99.89	99.92	99.89	99.89	99.90
Systech	99.65	99.69	99.60	99.68	99.74	99.58
Worldwide	99.90	99.87	99.91	99.88	99.92	99.91

Reasons for Non-Communication

On-Board Computer Problems: Although the computers installed in todays vehicles are relatively rugged, some do fail during the life of the vehicle.
Blown Fuse: Some vehicles use accessory-related fuses to power the vehicle's Data Link Connector. These may need to be checked and replaced if blown.
Cigarette Smoke: Residue from cigarette smoke can coat the pins on the Data Link Connector causing a high resistance to signals being transmitted. These pins can be cleaned with electronic cleaner.

Alternate steps to take if the vehicle still fails to communicate:

First - Turn the ignition key to the engine off position
Second - Remove the key from the ignition switch
Third - Disconnect the emission analyzer cable from the vehicle's Data Link Connector
Fourth - Wait 30 seconds in order to allow the vehicle's On-Board computer to fully power down
Fifth - Reconnect the emission analyzer cable to the vehicle's Data Link Connector
Sixth - Insert the key into the ignition switch
Seventh - Start the engine and continue with the test as directed by analyzer

For more information, contact Paul Gordey at (919) 715-7220 or Paul.Gordey@ncmail.net