With "SCAN" Tool

A "SCAN" tool provides a visual reading of most of the ECM inputs and some of the outputs controlled by the ECM. With the "SCAN" tool in the code position, the stored code will be displayed in the display window.

By connecting the "SCAN" tool to the ALDL connector and a 12-volt power supply, valuable information can be received from the CCC system. The technician's knowledge of the system and understanding of the "SCAN" tool's limitations can provide information that would otherwise be difficult to obtain. However, "SCAN" tools cannot replace volt/ohmmeters when called for within diagnostic charts.

The "SCAN" tool can display the following information in the display window:

• "ON" when ECM has commanded A/C clutch into operation. This does not mean that A/C clutch is operating, only that ECM has instructed it to commence operation.
• "YES" when A/C is activated.
• Actual battery voltage reading detected at ECM ignition input.
• "Closed Loop" or "Open Loop", depending upon mode that engine control system is operating under.
• Diagnostic codes.
• Coolant temperature in degrees Centigrade.
• RPM that ECM is trying to maintain at idle.
• "ON" when ECM has commanded EGR valve to open. This does not mean that EGR valve is open, only that ECM has instructed EGR valve to open to allow EGR flow.
• Position of EGR valve pintle.
• "YES" when transmission is in fourth gear.
• A number that represents the position that the ECM thinks the idle air control valve is in at that time.
• A number, in milliseconds, that represents the pulse width ("on" time) that the ECM is commanding to the injectors.
• Amount of spark retard in number of degrees.
• "YES" when knock is detected or "NO" when knock is not detected.
• Manifold air temperature in degrees Centigrade.
• Low voltage when the manifold pressure is low (high vacuum), or high voltage when the pressure is high (low vacuum).
• Vehicle speed in miles per hour.
• Oxygen sensor reading ranging from 1 to 999 millivolts. If consistently below 350 millivolts, fuel system is lean; if consistently above 550 millivolts, fuel system is rich.
• Percent of throttle angle.

These are only some of the capabilities of the "SCAN" tool. Consult tool manufacturer's diagnostic manual for complete explanation of the tool and its limitations.