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Emissions / Exhaust

ASE L1: Understanding Scan Tool Modes

Section B, Item 8 of the ASE L1 certification task list states:
“Interpret OBD II scan tool data stream, diagnostic trouble codes (DTCs), freeze-frame data, system monitors, monitor readiness indicators, and trip and drive cycle information to determine system condition and verify repair effectiveness.” What ASE is talking about are the modes of OBD II scan tool protocol. Modes are usually denoted by a dollar sign and a two-digit number.

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“Interpret OBD II scan tool data stream, diagnostic trouble codes (DTCs), freeze-frame data, system monitors, monitor readiness ­indicators, and trip and drive cycle information to determine ­system condition and verify repair effectiveness.”
What ASE is talking about are the modes of OBD II scan tool ­protocol. Modes are usually denoted by a dollar sign and a two-digit number. While most rookie technicians can use a scan tool without being aware of what the modes mean, L1 certified technicians should know what the modes are for advance diagnostic and tool usage for some undercar systems like ABS and emissions.
Mode $01: Used to identify what powertrain information is available to the scan tool.
 
Mode $02: Displays freeze-frame data.
 
Mode $03: Lists the emission-related “confirmed” DTCs stored. It displays exact numeric, four-digit codes identifying the faults.
 
Mode $04: This mode is used to clear emission-related diagnostic information. This includes clearing the stored pending/confirmed DTCs and freeze-frame data.
 
Mode $05: Displays the oxygen sensor monitor screen and the tests.
 
Mode $06: This type of information is a request for On-Board Monitoring Test Results for Continuously and Non-Continuously Monitored Systems. There are typically a minimum value, a maximum value and a current value for each non-continuous monitor.
 
Mode $07: In this mode, the scan tool sends a request for emission-related DTCs detected during the current or last completed driving cycle. It enables the external test equipment to obtain “pending” DTCs detected during the current or last completed driving cycle for emission-related components/systems. This is used after a vehicle repair, and after clearing diagnostic information to see test results after a single driving cycle to determine if the repair has fixed the problem.
 
Mode $08: Bi-directional testing of components.
 
Mode $09: Retrieve vehicle information like the VIN and the calibration identification.
 
Mode $0: Lists emission-related “permanent” DTCs stored. As per CARB, any DTC that is commanding the MIL on and is stored into non-volatile memory will be logged as a permanent fault code.  

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