Magazine for the auto service professional
Issue link: http://asp.epubxp.com/i/780462
21 | ASP February 2017 Technical mode number indicates it's a hexadecimal number used by the computers involved.) Before any scan tool can communicate it needs to know what language the vehicle speaks. CAN, ISO 9141-2 and J1850 PWM are examples of communication protocols used. Once the scanner understands the vehicle's protocol, the PCM will allow the scanner access to current live powertrain data values or PIDs (parameter identification). is data must be actual sensor reading, not default, substituted or enhanced data that some manufacturers' factory data streams may provide. Many manufacturers' factory data streams (Fiat/Chrysler and Honda come to mind) may show false information that the PCM is sup- plying because it is aware of a failed sensor or skewed data and still wants the vehicle to run properly for the customer. It just bases the false information from another input or sensor but it doesn't tell you that when you are looking at the factory data. e vehicle's system readiness test status and the MIL status are also displayed in this mode. e fewer PIDs that are selected the faster the data refresh rate will be, and having genuine sensor data is a real help. Mode $02... Request the freeze frame information. Mode $02 provides the data stored at the time the fault was detected by the OBD-II and when the OBD-II system turned on the MIL. Mode $02 output only shows the data from when the code set or matured and caused the MIL. is is important to note, because it may not provide information on when the actual problem started, but it provides clues and these clues can still be useful in replicating the failure conditions. I frequently use the freeze frame data in Mode $02 to diagnose a Toyota Matrix P0171 lean code in the winter. ese vehicles typically aren't running lean when I see them, but the Mode $02 freeze frame data shows the outside temperature when the code set was -20 degrees Fahrenheit and the intake manifold gaskets are as hard as rock and unable to seal properly (that's why it always runs fine by the time I see it). Be aware that the freeze frame data can be overwritten by higher priority DTCs, (a misfire code, for example, will overwrite a lean code) and all of the Mode $02 data be cleared when the codes are cleared. Mode $03... Request the emissions-related diagnostic trouble codes. Mode $03 allows our scanner access to the stored DTCs in the PCM. ese emissions related codes will be "P0, P2 or P34-P39" generic codes or "P1 or Among the numerous tools in my shop's arsenal, these are my three favorite generic OBD-II scanners that I use, even though one is a specialized VW/Audi tool (its OBD-II capabilities are fabulous).