Diagnostics Operations Generic OBD II Operations
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Stored Codes
Stored codes are the current emission related DTCs from the ECM of the
vehicle. OBD II/EOBD Codes have a priority according to their emission
severity, with higher priority codes overwriting lower priority codes. The
priority of the code determines the illumination of the MIL and the codes
erase procedure. Manufacturers rank codes differently, so expect to see
differences between makes.
Pending Codes
These are codes whose setting conditions were met during the last drive
cycle, but need to be met on two or more consecutive drive cycles before
the DTC actually sets. The intended use of this service is to assist the
service technician after a vehicle repair and after clearing diagnostic
information, by reporting test results after a single driving cycle.
a) If a test failed during the driving cycle, the DTC associated with that
test is reported. If the pending fault does not occur again within 40 to
80 warm-up cycles, the fault is automatically cleared from memory.
b) Test results reported by this service do not necessarily indicate a
faulty component or system. If test results indicate another failure
after additional driving, then a DTC is set to indicate a faulty
component or system, and the MIL is illuminated.
Freeze Frame
In most cases the stored frame is the last DTC that occurred. Certain
DTCs, those that have a greater impact on vehicle emission, have a
higher priority. In these cases, the highest priority DTC is the one for
which the freeze frame records are retained. Freeze frame data includes
a “snapshot” of critical parameter values at the time the DTC is set.
Erase Codes
This option is used to clear all emission related diagnostic data such as,
DTCs, freeze frame data and manufacturer specific enhanced data from
the vehicle’s ECM, and resets the I/M Readiness Monitor Status for all
vehicle monitors to Not Ready or Not Complete status.
A confirmation screen displays when the clear codes option is selected to
prevent accidental loss of data. Select Yes on the confirmation screen to
continue, or No to exit.
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