Open circuit check
Possible causes for the open circuits are as follows. As the cause can exist in the connector/coupler or terminal, they need to be checked carefully.
Loose connection of connector/coupler.
Poor contact of terminal (due to dirt, corrosion or rust, poor contact tension, entry of foreign object etc.).
Wire harness being open.
Poor terminal-to-wire connection.
Disconnect the negative cable from the battery.
Check each connector/coupler at both ends of the circuit being checked for loose connection. Also check for condition of the coupler lock if equipped.
(1) Sensor; (2) ECM; (A) Check for loose connection.
Using a test male terminal, check the female terminals of the circuit being checked for contact tension.
Check each terminal visually for poor contact (possibly caused by dirt, corrosion, rust, entry of foreign object, etc.). At the same time, check to make sure that each terminal is fully inserted in the coupler and locked.
If contact tension is not enough, rectify the contact to increase tension or replace.
The terminals must be clean and free of any foreign material which could impede proper terminal contact.
(A) Check contact tension by inserting and removing; (B) Check each terminal for bend and proper alignment.
Using continuity inspect or voltage check procedure as described below, inspect the wire harness terminals for open circuit and poor connection. Locate abnormality, if any.
(1) Looseness of crimping; (2) Open; (3) Thin wire (a few strands left)
Continuity check
Measure resistance across coupler (B) (between (A) and (C) in the figure).
If no continuity is indicated (infinity or over limit), the circuit is open between terminals (A) and (C).
(1) ECM
Disconnect the coupler (B) and measure resistance between couplers (A) and (B).
If no continuity is indicated, the circuit is open between couplers (A) and (B). If continuity is indicated, there is an open circuit between couplers (B)' and (C) or an abnormality in coupler (B)' or coupler (C).
(1) ECM
Voltage check
If voltage is supplied to the circuit being checked, voltage check can be used as circuit check.
With all connectors/couplers connected and voltage applied to the circuit being checked, measure voltage between each terminal and body ground.
If measurements were taken as shown in the figure at the right and results are as listed below, it means that the circuit is open between terminals (A) and (B).
Voltage Between:
- (C) and body ground: Approx. 5 V
- (B) and body ground: Approx. 5 V
- (A) and body ground: 0 V
Also, if measured values are as listed below, a resistance (abnormality) exists which causes the voltage drop in the circuit between terminals (A) and (B).
Voltage Between:
- (C) and body ground: Approx. 5 V
- (B) and body ground: Approx. 5 V → 2 V voltage drop
- (A) and body ground: 3 V → 2 V voltage drop
Short circuit check (wire harness to ground)
Disconnect the negative cable from the battery.
Disconnect the connectors/couplers at both ends of the circuit to be checked.
Note: If the circuit to be checked branches to other parts as shown, disconnect all connectors/couplers of those parts. Otherwise, diagnosis will be misled.
Measure resistance between terminal at one end of circuit ((A) terminal in figure) and body ground. If continuity is indicated, there is a short circuit to ground between terminals (A) and (C).
(1) To other parts; (2) Other parts
Disconnect the connector/coupler included in circuit (coupler (B)) and measure resistance between terminal (A) and body ground.
If continuity is indicated, the circuit is shorted to the ground between terminals (A) and (B).
(1) To other parts; (2) ECM