Electrical Circuit Inspection Procedure

Open Circuit Test

Procedures for Open Circuit
- Continuity Check
- Voltage Check
If an open circuit occurs (as seen in [FIG. 1]), it can be found by performing Step 2 (Continuity Check Method) or Step 3 (Voltage Check Method) as shown below.

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Continuity Check Method

NOTE:

When measuring the resistance, lightly shake the wire harness vertically or horizontally.

Specification (Resistance)

1Ω or less → Normal Circuit

1MΩ or Higher → Open Circuit

Disconnect connectors (A) and (C), and measure resistance between connectors (A) and (C) as shown in [FIG. 2].

In [FIG. 2], if the measured resistances in lines 1 and 2 are "over 1 MΩ" and "below 1Ω" respectively, line 1 has an open circuit. (Line 2 is normal.) To find the exact broken point, check the sub line of line 1 as described in the next step.

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Disconnect connector (B), and measure the resistances between connectors (C) and (B1), and between (B2) and (A) as shown in [FIG. 3].

In this case, the measured resistance between connectors (C) and (B1) is higher than 1 MΩ and the open circuit is between terminal 1 of connector (C) and terminal 1 of connector (B1).

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Voltage Check Method

With each connector still connected, measure the voltage between the chassis ground and terminal 1 of each of connectors (A), (B) and (C) as shown in [FIG. 4].

The measured voltages of connectors are 5V, 5V and 0V respectively. So the open circuit is between connectors (C) and (B).

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Short Circuit Test

Test Method for Short to Ground Circuit

Continuity Check with Chassis Ground

If short to ground circuit occurs as shown in [FIG. 5], the broken point can be found by performing Step 2 (Continuity Check Method with Chassis Ground) as shown below.

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Continuity Check Method (with Chassis Ground)

NOTE:

Lightly shake the wire harness vertically or horizontally when measuring the resistance.

Specification (Resistance)

1Ω or less → Short to Ground Circuit

1MΩ or Higher → Normal Circuit

Disconnect connectors (A) and (C), and measure the resistance between connector (A) and Chassis Ground as shown in [FIG. 6].

If the measured resistances in lines 1 and 2 are "below 1 Ω" and "over 1 MΩ" respectively, line 1 has an open circuit. (Line 2 is normal.) To find the exact broken point, check the sub line of line 1 as described in the next step.

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Disconnect connector (B), and measure the resistances between connector (A) and chassis ground, and between (B1) and chassis ground as shown in [FIG. 7].

The measured resistance between connector (B1) and chassis ground is 1Ω or less. The short to ground circuit is between terminal 1 of connector (C) and terminal 1 of connector (B1).

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Voltage Drop Test
This test checks for voltage drop along a wire, or through a connection or a switch.
1. Connect the positive lead of a voltmeter to the end of the wire (or to the side of the connector or switch) closest to the battery.
2. Connect the negative lead to the other end of the wire (or the other side of the connector or switch).
3. Operate the circuit.
4. The voltmeter will show the difference in voltage between the two points. A difference, or drop of more than 0.1 volts (50 mV in 5V circuits), may indicate a problem. Check the circuit for loose or dirty connections.