Blue point Microscan III Instrukcja Użytkownika Pobierz pdf (Strona 21)

On-Board Diagnostics (OBD) Basics Diagnostic Service Definitions

Using Freeze Frame for Diagnostic Purposes

Freeze Frame is useful for determining the exact conditions the vehicle was operating under when

the DTC was set.

NOTE:

i Freeze Frame is captured and stored when the DTC is set, not when the problem began.

For example, misfire is evaluated every 1000 rpm. A misfire DTC may be stored 60 to 90 seconds

after the misfire initially occurred, at substantially different speed and load conditions.

The Technician can duplicate these conditions to verify the complaint or the repair. In some cases

the on-board tests for a specific DTC may report no problem found. But when the conditions match

the Freeze Frame conditions, that same DTC would set with the MIL on.

NOTE:

i Freeze Frame data is erased whenever codes are cleared.

Does a stored DTC change?

It can be overwritten by higher priority Emission DTCs. Misfire and Fuel System DTCs have the

highest priority. A lower rated DTC may be overwritten by a higher priority DTC.

Only data parameters supported by the ECM are included in the Freeze Frame data list.

4.4.3 Service $03:

Emission-related DTCs

The purpose of this service is to enable the scan tool to obtain stored DTCs from the power train

ECMs that are emission-related.

The OBD-I ECM primarily identifies a faulty signal or a faulty sensor using three steps:

• Signal or component shorted to ground

• Signal or component shorted to battery positive

• No signal or component (open circuit)

For each of these tests, a specific trouble code is set.

With OBD-II/EOBD, expanded diagnostics now includes “rationality” testing. One input signal is

compared against other input signals to determine if the reading is reasonable, given the current

operating conditions.

All OBD-II/EOBD/JOBD codes use a five character format that identifies the control system and

the type of failure detected. Generic codes are the same for all manufacturers, while enhanced

codes are unique to a specific manufacturer.

1 2 ... 16 17 18 19 20 21 22 23 24 25 26 ... 71 72

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Blue point Microscan III Instrukcja Użytkownika Strona 21