Control Module and DTCs
Control Module Learning AbilityThe control module has a learning ability which allows the control module to make corrections for minor variations in the fuel system in order to improve driveability. Whenever the battery cable is disconnected, the learning process resets.
The driver may note a change in vehicle performance. In order to allow the PCM to re-learn to drive the vehicle at part throttle with moderate acceleration. The vehicle may also operate at idle conditions until the normal performance returns.
Reprogramming (Flashing) the Control Module
Some vehicles allow the reprogramming of the control module without removal from the vehicle. This provides a flexible and a cost-effective method of making changes in software and calibrations.
Refer to the latest Techline information on reprogramming or flashing procedures.
Verifying Vehicle Repair
Verification of the vehicle repair will be more comprehensive for vehicles with OBD II system diagnostics. Following a repair, the technician should perform the following steps:
1. Review the fail records and the Freeze Fame data for the DTC which was diagnosed. Record the fail records or Freeze Fame data. The Freeze Frame data will only store for an A or B type diagnostic and only if the MIL has illuminated.
2. Clear the DTCs.
3. Operate the vehicle within the conditions noted in the fail records or the Freeze Frame data.
4. Monitor the DTC status information for the specific DTC which has been diagnosed until the diagnostic test associated with that DTC runs.
Following these steps are very important in verifying repairs on the OBD II systems. Failure to follow these steps could result in an unnecessary repair.
Reading Diagnostic Trouble Codes
Use a diagnostic scan tool in order to read the diagnostic trouble codes. Failure to follow this step could result in unnecessary repairs.
Clearing Diagnostic Trouble Codes
In order to clear Diagnostic Trouble Codes (DTCs), use the diagnostic scan tool clear DTCs or clear info function. When clearing DTCs follow the instructions supplied by the tool manufacturer When a scan tool is not available, disconnecting one of the following sources for at least thirty (30) seconds can also clear the DTCs:
Notice: Turn off the ignition key when disconnecting or reconnecting battery power in order to prevent system damage.
^ The power source to the control module. Examples include the following:
- Fuse
- Pigtail at battery Control Module connectors etc.
^ The negative battery cable
Disconnecting the negative battery cable may result in the loss of other on-board memory data, such as preset radio tuning.
DTC Modes
The OBD II vehicles have three options available in the scan tool DTC mode in order to display the enhanced information available. A description of the new modes, the DTC Info and the Specific DTC, follows. After selecting the DTC, the following menu appears:
^ The DTC Info
^ The Specific DTC
^ The Freeze Frame
^ The Fail Records
^ The Clear Info
The following is a brief description of each of the sub menus in the DTC Info and the Specific DTC. The order in which they appear here is alphabetical and not necessarily the way they will appear on the scan tool.
DTC Info Mode
Use the DTC Info mode in order to search for a specific type of stored DTC information. There are seven choices. The electronic service information may instruct the technician to test for DTCs in a certain manner. Always follow the published service procedures.
In order to get a complete description of any status, press the Enter key before pressing the desired F-key. For example, pressing enter, then an F key will display a definition of the abbreviated scan tool status.
DTC Status
This selection displays any DTCs that have not run during the current ignition cycle or have reported a test failure during this ignition up to a maximum of 33 DTCs. The DTC tests which run and pass removes that DTC number from the scan tool screen.
Fail This Ign. (Fail This Ignition)
This selection displays all of the DTCs that have failed during the present ignition cycle.
History
This selection displays only the DTCs that are stored to the history memory of the control module. The history memory will not display the Type B DTC that have not requested the MIL. The history memory will display all of the type A and B DTCs that have the MIL and have tailed within the last 40 warm-up cycles. In addition, the history memory will display all of the type C DTCs that have failed within the last 40 warm-up cycles.
Last Test Fail
This selection displays only the DTCs which have failed during the last time that the test ran. The last test may have ran during a previous ignition cycle if the a type A or B DTC is displayed. For type C DTCs, the last failure must have occurred during the current ignition cycle to appear as Last Test Fail.
MIL Request
This selection displays only the DTCs that are requesting the MIL. Type C DTCs cannot be displayed by using this option. This selection will report type B DTCs only after the MIL has been requested.
Not Run SCC (Not Run Since Code Clear)
This option displays up to 33 DTCs that have not run since the DTCs were last cleared. Since any displayed DTCs have not run, their condition (passing or failing) is unknown.
Test Fail SCC (Test Failed Since Code Clear)
This selection displays all of the active and history DTCs that have reported a test failure since the last time the DTCs were cleared. The DTCs that last failed over 40 warm-up cycles (before this option is selected) will not be displayed
Specific DTC Mode
This mode is used in order to check the status of the individual diagnostic tests by the DTC number. This selection can be accessed if a DTC has passed or failed. Many OBD II DTC mode descriptions are possible because of the extensive amount of information that the Diagnostic Executive monitors regarding each test. Some of the many possible descriptions follow with a brief explanation.
This selection only allows the entry of the DTC numbers that are supported by the vehicle that is being tested. If an attempt is made to enter the DTC numbers for tests which the diagnostic executive does not recognize, the requested information will not be displayed correctly and the scan tool may display an error message. The same applies to using the DTC trigger option in the Snapshot mode. If an invalid DTC is entered, the scan tool will not trigger.
Failed Last Test
For type A and B DTCs, this message will display during the subsequent ignition cycles until the test passes or the DTCs are cleared. For type C DTCs, this message clears whenever the ignition is cycled.
Failed Since Clear
This message displayed indicates that the diagnostic test failed at least once within the last 40 warm-up cycles since the last time the control module cleared the DTCs.
Failed This Ign. (Failed This Ignition)
This message displayed indicates that the diagnostic test has failed at least once during the current ignition cycle. This message will clear when the DTCs are cleared or the ignition is cycled.
History DTC
This message displayed indicates that the DTC has stored to memory as a valid fault. A DTC displayed as a History fault does not necessarily mean that the fault is no longer present. The history description means that all of the conditions necessary for reporting a fault have met.
MIL Requested
This message displayed indicates that the DTC is currently causing the MIL to turn ON. Remember that only type A and B DTCs can request the MIL. The MIL request cannot determine if the DTC fault conditions are currently being experienced. This is because the diagnostic executive requires up to 3 trips during which the diagnostic test passes to turn OFF the MIL.
Not Run Since Cl (Not Run Since Cleared)
This message displayed indicates that the selected diagnostic test has not run since the last time the DTCs were cleared. Therefore, the diagnostic test status (passing or failing) is unknown. After the DTCs are cleared, this message continues to be displayed until the diagnostic test runs.
Not Run This Ign. (Not Run This Ignition)
This message displayed indicates that the selected diagnostic test has not run this ignition cycle.
Test Ran and Passed
This message displayed indicates that the selected diagnostic test has the following items:
^ Passed the last test
^ Ran and passed during this ignition cycle
^ Ran and passed since the DTCs were last cleared
^ This test has not failed since the DTCs were last cleared.
Whenever the indicated status of the vehicle is Test Ran and Passed after a repair verification, the vehicle is ready to be released to the customer.
If the indicated status of the vehicle is Failed This Ign. after a repair verification, then the repair is incomplete. A further diagnosis is required.
Prior to repairing a vehicle, use the status information in order to evaluate the state of the diagnostic test and to help identify an intermittent problem. The technician can conclude that although the MIL is illuminated, the fault condition that caused the code to set is not present. An intermittent condition must be the cause.