Remove the cruise control ecu assy with connector still connected.
disconnect the ecm connector.
turn the ignition switch to on.
measure voltage between terminal 13 (idl) of cruise control ecu assy connector and body ground when the throttle valve is fully closed and fully opened.
Ok:
2 Check harness and connector(between cruise control ecu assy and ecm)
Check for open and short circuit in harness and connector between cruise control ecu assy and ecm
Check and replace cruise control ecu assy
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Test yourself
A quick Toyota Corolla quiz: every answer comes with an explanation and a link to the manual page.