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.