Toyota Corolla (E120) 2002–2008 Repair Manual / Introduction / How to troubleshoot ecu controlled systems / Electronic circuit inspection procedure / Check open circuit

Toyota Corolla (E120): Check open circuit

1. For the open circuit in the wire harness in fig. 1, Perform a resistance check in step (b) or a voltage check in step (c) to locate the section.

2. Check the resistance.

1.  Disconnect connectors a and c and measure the resistance between them.

   Resistance: 1 Ω or less

Hint

: measure the resistance while lightly shaking the wire harness vertically and horizontally. In the case of fig. 2: Between terminal 1 of connector a and terminal 1 of connector c " 10 kΩ

or higher between terminal 2 of connector a and terminal 2 of connector c " below 1 Ω

therefore, the cause 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 the connectors.

   In the case of fig. 3: Between terminal 1 of connector a and terminal 1 of connector b1 " below 1 w between terminal 1 of connector b2 and terminal 1 of connector c " 10 kw therefore, the cause is an open circuit between terminal 1 of connector b2 and terminal 1 of connector c.

3. Check the voltage.

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

   As shown in fig. 4, With each connector still connected, measure the voltage between the body ground and terminal 1 of connector a at the ecu 5 v output terminal, terminal 1 of connector b, and terminal 1 of connector c, in that order.

2.  If the results are: 5 v: between terminal 1 of connector a and body ground 5 v: between terminal 1 of connector b and body ground 0 v: between terminal 1 of connector c and body ground therefore, the cause is an open circuit in the wire harness between terminal 1 of connector b and terminal 1 of connector c.