Actron 9640A manual GM Enhanced OBD II Diagnostics, Readiness, Nostics

GM Enhanced (OBD II) Diagnostics

GM ENHANCED (OBD II) DIAGNOSTICS

IMPORTANT

This system applies to GM vehicles manufactured from 1996 to present. Some GM vehicles in 1994 and 1995 were equipped with this system. Refer to “Appendix A - Data Link Connectors". GM vehicles manufactured from 2000 to present automatically use Global OBD II Diagnostics.

✓If an Error Message displays, make sure the OBD II connector is securely attached, and the ignition key is ON. Cycle the ignition key to OFF for 10 seconds, then ON. This may be required to reset the computer. If required, select YES to try again. If the problem still exists, refer to “Error Messages” on page 8-2.

✓On the initial link to the vehicle, the scan tool checks the status of the I/M Monitors and conveys it to the operator, no matter which function is selected.

✓Specific GM Enhanced functions are defined in this section. Refer to “Sec- tion 4 - Global OBD II Diagnostics" for other functions.

The first time the scan tool communicates with the vehicle, the communication type is automatically detected, and is used until the scan tool is turned OFF or another vehicle is diagnosed.

Manual Info

TheManualInfo function, the last one in the function list, instructs the user what section of the manual to use. This section coversGMEnhanced(OBDII)Diag-

nostics.	5
I/M Readiness
Refer to “I/M Readiness” on page 4-1 of Global OBD II Diagnostics.
Read Codes

TheReadCodes function retrieves Diagnostic Trouble Codes (DTCs) from the vehicle’s computer module(s). This function can be performed with the KOEO or KOER. These codes cause the computer to illuminate the Malfunction Indi- cator Lamp (MIL) when an emission-related or driveability fault occurs. The MIL is also known as the “service engine soon” or “check engine” lamp.

For the Enhanced OBD II system, GM added a third code type, Transient codes. The types are defined below:

•History Codes — intermittent codes placed in the vehicle’s memory when the trouble originally occurred, and will remain there even if the trouble has been corrected. If no trouble after 50 engine warm-up cycles, the DTC will be erased.

•CurrentCodes — codes transmitted through the PCM’s data stream when a trouble condition is active and cannot be erased. The problem must be repaired to remove the DTC.

•Transient Codes — indicates the current code has been set at least once but possibly not enough to cause a history code to be stored.

In GM Enhanced OBD II, if DTCs are present, then three conditions (or sta- tuses) accompany each DTC definition.

•MIL (Malfunction Indicator Lamp): REQUESTED or NOT REQUESTED An emissions-related DTC is requesting the MIL (Check Engine/Service Engine Soon) to be ON.

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