Actron 9640A GM Historic OBD I Diagnostics, Manual Info, Read Codes, Tool Will retrieve the DTCs

Section 5 – GM Diagnostics

✓If the Scan Tool displays an Error Message, make sure the cables and adapters are securely attached and the ignition key is ON. Cycle the igni- tion key to OFF for 10 seconds, then ON. Attempt the test selected again. If the problem remains, refer to “Error Messages” on page 8-2.

GM HISTORIC (OBD I) DIAGNOSTICS

✓Some 1994 and 1995 vehicles use the 16-pin OBD II connector, but are not OBD II compliant. They still use the OBD I application software. Refer to “Appendix A - Data Link Connectors".

Manual Info

TheManualInfo function instructs the user what section of the manual to use. This section covers GM Historic (OBD I) Diagnostics.

Read Codes

The Read Codes function is used to retrieve all stored Diagnostic Trouble Codes (DTCs) from the control module(s). This can be performed with key ON engine OFF (KOEO) or key ON engine RUNNING (KOER). Two types of codes were used by GM in the Historic System: Current codes and History codes. Prior to 1986, all codes were referred as Current Codes. From 1986 through 1995, both codes were used as the PCM was able to differentiate them.

The tool automatically displays the type of codes that pertain to the vehicle 5 under test. The DTC types are defined as follows:

•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 erases.

•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.

✓On some vehicles, all codes are Current Codes, because the PCM cannot distinguish Current Codes from History Codes. The only way to determine this is to erase the code and then drive the vehicle to see if the code returns.

Perform the following:

1)Set Parking Brake

2)Turn Key On-Engine Off or Running.

3)Put Transmission In Park Or Neutral.

SelectReadCodes from the GM Func-
tion List and press	. The tool
will retrieve the DTCs.
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