Initial Inspection and Diagnostic Overview

Input signals for sensors are monitored by the computer (ECU). The computer stores the operating conditions of these sensors in its memory, and these operating conditions can be ``read'' from the memory using a voltmeter and adapter. The computer is capable of storing information for all of these sensors except the oxygen sensor, even if the ignition switch is turned to the ``Off'' position. With the ignition switch in the ``Off'' position, the malfunctioning signal of the oxygen sensor is lost.
When diagnosing system malfunctions using ``Self Diagnosis,'' the following precautions must be observed. When battery voltage is low, no detection of input signal malfunctions can be made. Ensure battery is fully charged prior to testing. Ensure all malfunctioning codes are ``read'' prior to disconnecting battery cable. When testing for malfunctioning oxygen sensor, road test vehicle to bring engine to normal operating temperature, then test for oxygen sensor malfunction with engine running. After testing and corrections are made, clear trouble code(s) from computer memory.