Fault checking procedures
Check according to the following 5 steps
1. Verify the dissatisfaction of the user
It shall check the faulty circuit components
complained by the user and make record for the
correct repair and maintenance. It is forbidden to
dismantle the vehicle before
2. Circuit diagram interpretation and analysis
Analyze and judge the whole circuit of the faulty
component from power supply to ground wire
according to the system circuit diagram, and confirm
the operating method. If fails to judge the operating
method, refer to the circuit working reference. And
inspect other public circuits of the faulty circuit. Such
as the public system circuits of fuse, ground wire and
cutout on the circuit diagram. Inspect the public
circuits failed to be checked in the first step. If the
public circuits work normally, the problem lies in the
circuit itself. If several circuits are problematic in the
same time, it may be the problem of fuse or ground
wire.
3. Circuit and component inspection
Inspect it for the second step by testers. Effective
fault diagnosis shall be logical and simple operating
process. It shall confirm the fault causes by fault
diagnosis procedures or table. Start from the most
possible reason and easiest checking component.
4,Fault maintenance
Repair necessarily in case of any fault.
5. Confirm circuit operation
After finished repairing, it shall recheck to confirm
the fault has been removed. In case of fuse burnout, it
shall inspect all circuits publicly using this fusible
wire
Fault diagnosis devices
Voltmeter and test lamp
It can use test light or voltmeter to check circuit
status and use test light to check whether there is
voltage or not. The test light is composed of a pair of
guide wire and 12V bulb. In inspection, one piece of
guide wire connects to the ground wire while the
other connects to certain measuring point. If the light
turns on, this point is supplied with power.
Notice
When checking the voltage of electronic control
module, such as the engine control module (ECM) of
the electronic fuel injection engine, it shall
(necessarily) use digital voltmeter with 10M or
higher resistance to check. Checking the module
circuit by test light may be damage the internal
circuit. Therefore, never use test light to check the
electrical circuits.
The application methods of voltmeter and test light
are basically the same. The difference lies in the test
light can only check whether there is voltage while
the voltmeter can display the value of voltage.
Test light and resistance meter with self contained
power
Check whether the circuit is accessible by the test
light and resistance meter with self contained power.
The test light with self contained power supply is
composed of bulb, battery and two pieces of guide
wire. The bulb turns on if the two pieces of guide
wire connect. Before inspection, it shall dismantle
battery negative guide wire and pull out the fuse of
this circuit.