Advanced Automotive Fault Diagnosis
Test lights and analogue
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LÔØI NOÙI ÑAÀU, ledklok
- Điều hướng trang này:
- 2.5.3 Generic electrical testing procedure
- Start Auxiliary systems diagnostic chart
| 2.5.2 Test lights and analogue
meters – warning! A test lamp is ideal for tracing faults in say a lighting circuit because it will cause a current to flow which tests out high resistance connections. However, it is this same property that will dam- age delicate electronic circuits – so don’t use it for any circuit that contains an electronic control unit (ECU). Even an analogue voltmeter can cause enough current to flow to at best give you a false reading and at worst damage an ECU – so don’t use it! A digital multimeter is ideal for all forms of testing. Most have an internal resistance in excess of 10 M⍀. This means that the current they draw is almost insignificant. An LED test lamp or a logic probe is also acceptable. 2.5.3 Generic electrical testing procedure The following procedure is very generic but with a little adaptation can be applied to any electrical system. Refer to manufacturer’s recom- mendations if in any doubt. The process of check- ing any system circuit is broadly as follows. Start Auxiliary systems diagnostic chart Hand and eye checks (loose wires, loose switches and other obvious faults)– all connections clean and tight. Check battery Check motor (including linkages) or actuator or bulb(s) – visual check Fuse continuity – (do not trust your eyes) check voltage at both sides with a meter or a test lamp Voltage supplies at the device/motor/ actuator/ bulb(s) are correct? If used does the relay click (this means the relay has operated it is not necessarily making contact)? Check item with separate fused supply if possible before condemning Supply to switch – battery volts No Yes Yes No Supply out of the switch and to the relay – battery volts Relay earth connection – note also that the relay may have a supply and that the control switch may make the earth connection End Supplies to relay (terminal 30 for example) – battery volts Feed out of the relay (terminal 87 for example) – battery volts) Voltage supply to the light within 0.5 V of the battery Earth circuit (continuity or voltage) – 0 ohms or 0 V |