Intermittent failures in electronic systems may be very difficult to detect and accurately diagnose. The modules test for different malfunctions under different vehicle conditions. For this reason, a thorough test drive is often needed in order to repeat a fault condition. If the system malfunction is not repeated during the test drive, a good description of the complaint may be useful in locating an intermittent condition. When an intermittent condition is suspected, check the related circuits for the following conditions:

History DTCs indicate that the module has previously detected a malfunction. The reason could be either that the malfunction is intermittent or that the system for which the DTC is set for is not currently active. If a module displays a history DTC and the cause cannot be easily found, try clearing the DTC and manually operating the system that the DTC applies to, or by using a scan tool to control the outputs for that system. Read the diagnostic aids and conditions for setting the DTC for information relating to the system. The following conditions may result in history DTCs: