The PCM Reset function allows the technician to command the scan tool to clear all emissions-related diagnostic information from the Powertrain Control Module (PCM). Emissions related codes are stored in the PCM until all the OBD II System monitors or components have been tested to satisfy a drive cycle without any other faults occurring. Refer to the OBD II Drive Cycle article in this section for additional information on this subject. The events listed below occur after the OBD II Drive Cycle is completed and the PCM Reset procedure is performed:
- The trouble code number total will be cleared
- All trouble codes will be cleared
- All Freeze Frame data will be cleared
- All Oxygen Sensor Test data will be cleared
- All OBD II System Monitors will have their status reset
Refer to your scan tool Operating Manual for specific instructions on how to perform a PCM Reset. The list of instructions should include:
- Turn the key off
- Perform the necessary vehicle preparation and visual inspection
- Connect the scan tool to the Data Link Connector (DLC).
- Turn the key on or start the vehicle
- Verify the scan tool is connected and communicating properly with the PCM
- Perform the PCM Reset step, then turn the key off and disconnect the scan tool
The Reset Counter counts the number of times the vehicle has been started since a trouble codes was set, erased, or the battery was disconnected. The number of starts can be used to help determine when a trouble code actually set. This information is recorded by the PCM and displayed on the scan tool as the RESET COUNTER.
When there are no codes stored in memory, the scan tool will display NO TROUBLE CODES FOUND and the Reset Counter will display RESET COUNT = XXX.
Two important pieces of information that can help speed up a diagnosis are code conditions (including all enable criteria), and the parameter information (PID) stored in the Freeze Frame at the moment a trouble code is set and stored in memory
To access the PCM, connect the Scan Tool to the appropriate DLC. Turn the ignition on to allow the vehicle to identify itself to the Scan Tool. Once communication is established with the PCM, select a function (codes, data, actuator tests, system tests, etc) from the tool main menu. The Scan Tool performs these functions by communicating with the vehicle modules through the data bus circuits.
To read trouble codes without a Scan Tool, cycle the key from "off" to "on" 3 times within 5 seconds. This test can establish whether the PCM is capable of responding to a request. It can also be used if the Scan Tool will not communicate.
The Scan Tool "talks" to the vehicle controllers on separate networks. The tool communicates with the PCM via the SCI Transmit and Receive circuits, and with other modules through the CCD or PCI data bus circuits.