Before starting the inspection for intermittent conditions, perform Diagnostic system check-automatic air conditioner controls to verify that all the following conditions are met.
Some of the procedures require a careful visual and physical inspection. Problems may be solved just by carrying out visual and physical inspections, which leads to saving valuable time. Check for the following conditions.
Intermittent conditions indicate the following.
If an intermittent condition exists, check for improperly installed electrical components. Inspect the installation status of any aftermarket add-on electronic devices, lights, etc. Verify that no aftermarket equipment is connected to the serial data circuit. Most intermittent conditions are caused by a defective wire harness or poor connections. Carefully inspect suspect connectors visually and physically for the following conditions.
Repair or replace connector terminals in the problem circuit in order to ensure proper contact pressure. It is necessary to remove the terminal from the connector body in order to inspect for poor terminal-to-wire harness connections. If the intermittent condition exists from the start and if the state continues, perform an inspection relating to the vehicle anti-theft system.
If any of the following is the cause, no DTC is stored.
Note
The following inspection items show possible causes for each symptom. There is no order to the procedure. If there are no abnormal scan tool readings, proceed in a logical order, starting with items that are easiest to inspect, or those that are most likely.
1) Wire harness and connector
Many of the circuits that have an intermittent open circuit or short circuit are often affected by the movement of wire harnesses and connectors due to vibrations, engine torque, bumps in the road, rough pavement, etc. Perform the following inspections if possible.
If moving the wire harness or connector affects the data displayed or the component or system operation, inspect the wire harness or connector, and repair as necessary.
2) Electrical connection or wire harness
Intermittent conditions are caused by poor wire harness connections, loose terminals, or problems in the wire harness. Check for the following conditions.
3) Power supply and ground of the control unit, and power supply and ground of the components
Poor power supply or ground connections can cause widely varying symptoms.
The control unit may have multiple power supply circuits, and there are also some system components that are connected to power supply circuits from locations other than the control unit. Inspect all control unit power supply circuits. It is also necessary to inspect the intermediate connections. A test lamp or a DMM is capable of indicating whether or not any voltage is present, but neither of them has the ability to determine whether sufficient current is flowing in the circuit. Check that the circuit can carry the current necessary to operate the components.
The control unit may have multiple ground circuits, and there are also some system components that are connected to ground circuits from locations other than the control unit. Inspect all control unit and system ground circuits. Inspect the ground points for contamination or improper tightening. Also inspect the connections at the component and in splice packs where applicable. Check that the circuit can carry the current necessary to operate the components.
4) Effects caused by temperature
An intermittent condition may occur when a component reaches the appropriate operating temperature. Intermittent conditions may also occur only when the temperature is low or only when it is high.
If the intermittent condition is caused by heat, check the data relating to the following items.
If the intermittent condition is attributed to low temperature, check the data related to the following items.
Note
Based on the information from the customer, determine if the malfunction is caused by temperature.
5) EMI and electrical noise
Some electronic components and circuits are sensitive to EMI or other types of electrical noise.
Inspect for wire harnesses that are placed too close to high-voltage or high-current components such as injection components, motors, and generators. These components may generate electrical noise which interferes with normal circuit operations.
Check for a surge voltage or surge current generated by a relay or switch malfunction. Normally, this problem will occur when the malfunctioning component is operating.
Inspect for improper installation of non-factory or aftermarket electronic equipment such as lights, radios, amplifiers, electric motors, remote starters, and alarm systems. Electromagnetic disturbance may occur while this electronic equipment is in use, but not when not in use.
Inspect the generator for a malfunctioning rectifier circuit that may be allowing AC noise into the electrical system.
Operate the vehicle with the DMM connected to the suspected circuit. An abnormal reading on the DMM when the problem occurs may help identify the problem.
The scan tool snapshot function allows the recording of data collected by the control unit. The snapshot function records data in chronological order and can perform data analysis from the recorded data. The scan tool also has a graph function which can be used to graph parameters individually or in combination with other parameters for comparison. The snapshot can be triggered manually at the time the symptom is noticed or set up in advance to be triggered when a DTC sets. Using the abnormal values in the recorded data, it is possible to identify systems and components that require detailed investigation.