How to Diagnose
HOW TO DIAGNOSEThe most important point in troubleshooting is to determine "Probable Cause." Once the probable causes are determined, parts to be checked can be limited to those associated with such probable causes. The determination of the probable causes must be based on a theory and be supported by facts and must not be based on intuition only.
TROUBLESHOOTING STEPS
If an attempt is made to solve a problem without going through correct steps for troubleshooting, the symptoms could become more complicated, resulting in failure to determine the causes correctly and making incorrect repairs. The four steps below should be followed in troubleshooting.
Observe the symptom carefully. Check if there are also other problems.
In determining the probable causes, if is necessary to study the wiring diagram to understand the circuit as a system. Knowledge of switches, relays and other parts is necessary for accurate analysis. The causes of similar problems in the past must be taken into account.
Troubleshooting is carried out by making step-by-step checks until the cause is found.
After the problems are corrected, be sure to check that the system operates correctly. Also check that new problems have not been caused by the repair.
INFORMATION FOR DIAGNOSIS
This information includes the harness diagrams as well as the individual circuit drawings, operational explanations, and troubleshooting hints for each component. The information is presented in the following manner:
1. Connector diagrams show the connector positions, etc., on the actual vehicle as well as the harness path.
2. Circuit diagrams show the configuration of the circuit with all switches in their normal positions.
3. Operational explanations include circuit drawings of voltage flow when the switch is operated and how the component operates in reaction.
4. Troubleshooting hints include numerous examples of problems which might occur, traced backward in a common-sense manner to the origin of the trouble. Problems whose origins may not be found in this manner are pursued through the various system circuits.
NOTE: Components of MFI, ETACS, etc. with ECU do not include 3 and 4 above. For this, refer to a relevant information which includes details of these components.
INSPECTION
1. Sight and sound checks
Check relay operation, blower motor rotation, light illumination, etc. Listen for a "click" when a relay cover is pushed down.
2. Simple checks
For example, if a headlight does not come on and a faulty fuse or poor grounding is suspected. Replace the fuse with a new one. Or use a jumper wire to ground the light to the body. Determine which part(s) is/are responsible for the problem.
3. Checking with instruments
Use an appropriate instrument in an adequate range and read the indication correctly.
INSPECTION INSTRUMENTS
For inspection, use the following instruments:
1. Test lights
A test light consists of a 12V bulb and lead wires. It is used to check voltages or short circuits.
2. Self-powered test light
A self-powered test light consists of a bulb, battery and lead wires connected in series. It is used to check continuity or grounding.
3. Jumper wire
CAUTION: Never use a jumper wire to connect a power supply directly to a load.
4. A jumper wire is used to close an open circuit.
5. Voltmeter
A voltmeter is used to measure the circuit voltage. Normally, the positive (red lead) probe is applied to the point of voltage measurement and the negative (black lead) probe to the body ground. Use a digital voltmeter to check for voltage drop before or after a component.
6. Ohmmeter
An ohmmeter is used to check continuity or measure resistance of a switch or coil. If the measuring range has been changed, the zero point must be adjusted before measurement.
CHECKING SWITCHES
In a circuit diagram, a switch is shown in the idle state.
1. Normally open or normally closed switch
Switches are classified into those which open the circuit and those which close the circuit when off.
2. Switch connection
This figure illustrates a complex switch. The continuity between terminals at each position is as indicated in the table.
CHECKING RELAYS
NOTE: The deenergized state means that no current is flowing through the coil. The energized state means that current is flowing through the coil.
When a normal closed relay as illustrated here is checked, there should be continuity between terminals 1 and 2 and between terminals 3 and 4 when the relay is deenergized. There should be no continuity between terminals 3 and 4 when the battery voltage and ground are applied to terminals 1 and 2.
1. When current flows through the coil of a relay, its core is magnetized to attract the iron piece, closing (ON) the contact at the tip of the iron piece. When the coil current is turned off, the iron piece returns to its original position by a spring, opening the contact (OFF).
2. By using a relay, a heavy current can be turned on and off by a switch using much less current. For example, in the circuit shown here, when the switch is turned on (closed), current flows to the coil of the relay. Then, its contact is turned on (closed) and the light comes on. The current flowing through the switch is much less than that for the light.
3. Relays may be classified as the normally open-type or the normally closed-type, depending on their contact construction.
CHECKING FUSES
A blade type fuse has test taps provided to allow checking of the fuse itself without removing it from the fuse block. The fuse is okay if the test light comes on when its one lead is connected to the test taps (one at a time) and the other lead is grounded. Remember to turn the ignition switch to ON to ensure all circuits are live.
CAUTIONS IN EVENT OF BLOWN FUSE
When a fuse is blown, there are two probable causes. One is that it is blown due to flow of current exceeding its rating. The other is that It is blown due to repeated on/off current flowing through it. Which of the two causes is responsible can be easily determined by visual check as described below.
1. Fuse blown due to current exceeding rating
The illustration shows the state of a fuse blown due to this cause. In this case, do not replace the fuse with a new one hastily since a current heavy enough to blow the fuse has flowed through it. First, check the circuit for shorts and check for abnormal electric parts. After correcting shorts or replacing parts, use only a fuse of the same capacity as a replacement. Never use a fuse of larger capacity than the original fuse. If a larger capacity fuse is used, electric parts or wiring could be damaged.
2. Fuse blown due to repeated turning current on and off The illustration shows the state of a fuse blown due to repeated current on/off. Normally, this type of problem occurs after a fairly long period of use and is less frequent than the above. In this case, simply replace with a new fuse of the same capacity.
CABLES AND WIRES CHECK
1. Check connections for looseness, rust, and stains.
2. Check terminals and wires for corrosion by battery electrolyte, etc.
3. Check terminals and wires for open circuit or impending open circuit.
4. Check wire insulation and coating for damage, cracks and wear.
5. Check conductive parts of terminals for contact with other metallic parts (vehicle body and other parts).
6. Check grounding parts to verify that there is complete continuity between attaching bolt(s) and vehicle body.
7. Check for incorrect wiring.
8. Check that harnesses are secured to prevent contact with sharp edges and corners or hot parts (exhaust manifold, pipe, etc.).
9. Check that harnesses are secured firmly to provide enough clearance from the fan pulley, fan belt, and other rotating or moving parts.
10 .Check that the harness between fixed parts (such as the vehicle body) and vibrating parts (such as the engine) are long enough to allow for vibration and movement.
BATTERY HANDLING
WARNING: Battery posts, terminals and related accessories contain lead and lead compounds. WASH HANDS AFTER HANDLING.
When checking or servicing does not require power from the vehicle battery, be sure to disconnect the cable from the battery (-) terminal. This will prevent problems that could be caused by a short circuit. Disconnect the (-) battery terminal first and reconnect it last.
GENERAL ELECTRICAL SYSTEM CHECK
A circuit consists of the power supply, switch, relay, load, ground, etc. There are various methods to check a circuit including an overall check, voltage check, short-circuit check, and continuity check. Each of the methods briefly described below apply only to circuits similar to the illustration.
1. VOLTAGE CHECK
1. Ground one lead wire of the test light. If a voltmeter is used instead of the test light, ground the grounding side lead wire.
2. Connect the other lead wire of the test light to the power side terminal of the switch connector. The test light should come on or the voltmeter should indicate a voltage.
3. Then, connect the test light or voltmeter to the motor connector. The test light should not come on, or the voltmeter should indicate no voltage. When the switch is turned on in this state, the test light should come on, or the voltmeter should indicate a voltage, with motor starting to run.
4. The circuit illustrated here is normal. If there is any problem, such as the motor failing to run, check voltages beginning at the connector nearest to the motor until the faulty part is identified.
2. SHORT-CIRCUIT CHECK
Because the fuse has blown, it is probable that there is a short circuit. Follow the procedures below to narrow down the short-circuit location.
STEP 1. Remove the blown fuse and connect the test light across the fuse terminals (Switch: OFF).
Q: Does the test light illuminate?
YES: Short-circuit exists between the fuse block and the switch. Repair the harness between the fuse block and the switch.
NO: Go to Step2.
STEP 2. Switch on the switch and disconnect the illumination light connector.
Q: Does the test light illuminate?
YES: Short-circuit exists between the switch and the connector. Repair the harness between the switch and the connector.
NO: Short-circuit exists between the connector and the illumination light. Repair the harness between the switch and the connector.
3. CONTINUITY CHECK
1. When the switch is in the "OFF" position, the self-powered test light should illuminate or the ohmmeter should read 0 ohm, only when the contact points of terminals 1 and 2 are connected.
2. When the switch is the "ON" position, the self-powered test light should come on or the ohmmeter should read 0 ohm, only when the contact points of terminals 3 and 4 are connected.