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Examples of Circuit Inspections

CIRCUIT TESTING EXAMPLES:
Actual examples of the inspection method for open circuit and short circuit and ECU fault testing are explained below.

OPEN CIRCUIT CHECKS

Fig. 1:




For the open circuit in the wire harness in Fig. 1 perform a Continuity Check or a Voltage Check to locate the faulty section.

Continuity Check
(1) Disconnect connectors and (A) and (C) measure the resistance betwen them.

Fig. 2:




In the case of Fig. 2,
- Between terminal 1 of connector (A) and terminal 1 of connector (C) - No continuity (open)

- Between terminal 2 of connector (A) and terminal 2 of connector (C) - Continuity

- Therefore, it is found out that there is an open circuit between terminal 1 of connector (A) and terminal 1 of connector (C).

(2) Disconnect connector (B) and measure the resistance between connectors (A) and (B), (B) and (C)

Fig 3:




In the case of Fig. 3,
- Between terminal 1 of connector (A) and terminal 1 of connector (B) - Continuity

- Between terminal 1 of connector (B) and terminal 1 of connector (C) - No Continuity (open)

- Therefore, it is found out that there is an open circuit between terminal 1 of connector (B) and terminal 1 of connector (C).

Voltage Check
(1) In a circuit in which voltage is applied (to the ECU connector terminal), an open circuit can be checked for by conducting a voltage check.

Fig. 4:




- As shown in Fig. 4, with each connector still connected, measure the voltage between body ground and terminal 1 of connector at the ECU 5 V output terminal, terminal 1 of connector (B), and terminal 1 of connector (B), in that order.

If the results are:
- 5.0 Volts: Between Terminal 1 of connector (A) and Body Ground

- 5.0 Volts: Between Terminal 1 of connector (B) and Body Ground

- O.0 Volts: Between Terminal 1 of connector (C) and Body Ground

Then it is found out that there is an open circuit in the wire harness between terminal 1 of (B) and terminal 1 of (C).

SHORT CIRCUIT CHECKS

Fig. 5:




If the wire harness is ground shorted as in Fig. 5, locate the section by conducting a "continuity with ground check".

Continuity with Ground Checks
1. Disconnect connectors (A) and (C) and measure the resistance between terminals 1 and 2 of connector (A) and body ground.

Fig. 6:




In the case of Fig. 6,
- Between terminal 1 of connector (A) and body ground - Continuity

- Between terminal 2 of connector (A) and body ground - No continuity (open)

Therefore, it is found out that there is a short circuit between terminal 1 of connector (B) and terminal 1 of connector (C).

2. Disconnect connector (B) and measure the resistance between terminal 1 of connector (B) and body ground, and terminal 1 of connector (B) and body ground.

Fig. 7:




- Between terminal 1 of connector (B) and body ground - No continuity (open)

- Between terminal 1 of connector (B) and body ground - Continuity

Therefore, it is found out that there is a short circuit between terminal 1 of connector (B) and terminal 1 of connector (C).


ECU CHECKS



(1) Measure the resistance between the ECU ground terminal and the body ground.

OK: 1 Ohm or less




2. Disconnect the ECU connector, check the ground terminals on the ECU side and the wire harness side for bend and check the contact pressure.