The US government mandated that all vehicles sold in the US beginning with 1996 model year (1994 for vehicles sold new in California) comply with a minimum set of diagnostic functions. These functions were primarily intended for vehicle service. However, the specification allows for real-time monitoring of many vehicle sensors. This real-time monitoring comes in handy when tuning a high performance vehicle and also when racing to inform the driver of engine conditions.

There are some limitations to the OBD2 functionality. First, manufacturers are not required to output all sensor data. Only a minimum set of data. Second, the specification requires a certain amount of time after a message is recieved before data can be requested. The reason this is an issue is becuase the ECU does not stream data. Instead, each sensor data has to be requested. When the ECU recieves a request, it then outputs data for the sensor requested. When the R900/R920/R2000 displays a single sensor, the update rate is 8 times per second. When displaying 2 sensors, the update rate is 4 times per second. For 3 sensors the update rate is 3 times per second. For this reason, it is not advantagous to display more than 3 sensors at a time. There are some OBD2 dataloggers on the market that claim as little as 1ms accuracy. This might sound good, but it's misleading because the absolute fastest update time that can be achieved using the ISO9141-2 protocol is 120ms. Which is when requesting only 1 sensor data.

The OBD2 specification does not require a manufacturer to use a particular communication protocol. Most import vehicles use the ISO9141-2 protocol, which the R900, R920 and R2000 are compatible with. Ford, GM and late model Chrysler vehicles use the J1850 protocol. Compatibility with this protocol is currently under development. Some new vehicle models use a CAN bus protocol. Compatibility with this protocol is also under development.

The OBD2 diagnostic port connector is always in the drivers footwell and is powered. So, there is only 1 cable to hook up. Installation is nothing more than plugging in the data link cable to the OBD2 connector.

Please note that when the vehicle ECU has stored DTC's, it may not output current sensor values. If you suspect that data being displayed is incorrect, then make sure all DTC's have been cleared. It is impossible for our OBD2 data monitors to show incorrect data as there is error correction as part of the communication protocol. The data values displayed on the screen are the values that the vehicle ECU is reading and sending to the data monitor.

There are a total of 5 protocols in use today:

By model year 2008, all vehicles sold in the United States must use the CAN protocol for diagnostics. Here is a handy chart showing protocol usage since 1996 for most vehicle makes and models.

A list of DTC's can be found on the codes page.