Modern computerized engines have made repairs complicated for backyard mechanics even while making diagnosing problems simpler. An onboard diagnostic (OBD) computer monitors sensors throughout the vehicle and, when a problem is detected, turns on the check engine light. The OBD also stores a code that, if the car is a 1996 model or newer, can be read with a scanner.
Pre-1996 Corollas use an older system of "blink codes." The OBD blinks the check-engine light in a combination of long and short blinks. A mechanic can cross-reference the blink pattern with a chart to determine where the OBD detected a malfunction.
Turn the ignition off and open the hood. Locate the connector box, a small plastic box just behind the main fuse with "Diagnostics" printed on top.
Open the box and use a short length of wire to connect terminals E1 and TE1. The terminals will be marked on the housing or there will be a location diagram on the inside of the box cover. Be careful not to connect other terminals.
Turn on the ignition switch. Do not start the engine and do not press the accelerator pedal.
Watch the check-engine light as the system powers up. A regular pattern of on-off-on-off (both "on" and "off" lasting about 1/4 second) means no trouble code is stored. An irregular pattern can be decoded to determine a stored diagnostic code.
Count the blinks, which come in groups of regular on-off patterns separated by a long "off" period. For instance, "1/2 second on, 1/2 second off, 1/2 second on, 1-1/2- second off, 1/2 second on" has a regular pattern of two blinks, a break, and one blink: this is code 21. The blink pattern of code 13 would be 1/2 second on, 1-1/2 seconds off, and three 1/2-second "on" intervals separated by 1/2-second "off" periods. Record the code.
Turn off the ignition and remove the wire. Check the code against the cross-reference chart in the owner's manual or on-line. The chart will indicate which electronic system or sensor is malfunctioning. Use that information to diagnose the problem and research necessary repairs.
