Inspection Procedures For Electrical Circuits And How To Perform

Basic inspection
1. Resistance inspection conditions for electrical parts
  1. Unless otherwise specified, all resistances are measured under an ambient temperature of 20°C. Wait until the engine has cooled after driving. If measuring right after driving a vehicle at a high ambient temperature, the resistance will not be at the specified value.
2. Connector handling
  1. To disconnect a connector with a lock, press the connector in the joining direction until the lock tab can be easily moved and release the lock.
  2. When disconnecting a connector, hold the connector only (not pulling the harness).
  3. Before connecting a connector, check that the terminals are not deformed, damaged, missing or similarly defective.
  4. When connecting a connector with a lock, insert securely until a locking sound is heard.
  5. If checking the connector with an electrical tester, use a mini test lead and measure from the rear of the connector (harness side).
    CAUTION:
    For waterproof connectors, connect directly to the sub-harness to measure as the measurement is not possible from the rear of a waterproof connector.
    
    Do not excessively move the inserted tester probe and be careful not to damage any terminals.
    Fig 1: Caution For Connector Handling
    Courtesy of SUBARU OF AMERICA, INC.
3. Connector inspection procedures
  1. With the connector connected, grasp the connector housing and check the insertion status and lock effectiveness. (engagement status)
  2. With the connector separated, lightly pull on the wire harness. (missing terminals, terminal swage conditions, broken core) Visually check for presence of rust, metallic fragments, water and bent terminals. (Corrosion, foreign material, terminal deformation)
    CAUTION: If testing female gold-plated terminals, always use a male gold-plated terminal.
    
    Fig 2: Pulling Connector Wire Harness
    Courtesy of SUBARU OF AMERICA, INC.
  3. Prepare a terminal similar to the male terminal and insert into the female terminal, and check the terminal contact pressure, engagement status and sliding weight.
    
    Fig 3: Checking Female Terminal For Contact Pressure, Engagement Status And Sliding Weight
    Courtesy of SUBARU OF AMERICA, INC.
4. Connector terminal repair procedures
  1. If contacts are dirty, clean using an airgun or soft cloth. Never use sandpaper or similar material to polish the contacts as such material will cause the plating to come off if used to polish such parts.
  2. If contact pressure is not normal, replace the female terminals. At this time, use gold-plated terminals for the female terminals if the male terminals of the corresponding part are gold plated (gold color), and use tin-plated if the male terminals are tinplated (silver color).
  3. If contacts are normal, clean contacts using an airgun or similar method and apply connector grease. (This is to prevent contact oxidation and wear.)
    
    Fig 4: Caution For Cleaning Terminals
    Courtesy of SUBARU OF AMERICA, INC.
5. Connector grease
  1. Connectors in locations likely to contact water such as the alternator and headlights are filled with grease (white) that prevents corrosion of terminals.
  2. Fill female terminals with connector grease if the connector grease is insufficient or terminals have been repaired.
    CAUTION:
    Make sure that no dust or other foreign material is adhering.
    
    Do not use a screwdriver or similar tool to fill grease.
  3. Although there is no problem if grease adheres to waterproof connector O-rings and rubber plugs, grease adhering to other rubber parts (such as weather stripping and grommets for wire harnesses) can result in deterioration and discoloration. If grease adheres to such parts, immediately wipe off the grease.
    
    Fig 5: Caution For Applying Connector Grease
    Courtesy of SUBARU OF AMERICA, INC.
6. Wire harness handling
  1. If the harness is removed, check wiring and clamp conditions before performing the procedures so that it can be securely restored.
  2. Do not twist or pull harnesses, and allow no more slack than necessary.
  3. Do not allow harnesses to be interfered with by any high-temperature locations, rotating parts, sliding parts, vibrating parts, or parts with sharp angles (such as panel edges and screw tips).
  4. Make sure that harnesses are not pinched when installing parts.
  5. Harness covering must not be damaged. If damaged, replace or repair thoroughly using vinyl tape.
    
    Fig 6: Caution For Wire Harness Handling
    Courtesy of SUBARU OF AMERICA, INC.
Open circuit inspection
1. Perform a resistance or voltage test for the open circuits of the wire harness shown in Fig 7 to determine the location of the cause.
  
  Fig 7: Testing For Open Circuits Of Wire Harness
  Courtesy of SUBARU OF AMERICA, INC.
2. Measure the resistance.
  1. Disconnect connectors A and C, and measure the resistance between them.
    Standard value: Less than 1 Ω
    
    NOTE: Measure the resistance while lightly shaking the wire harnesses up/down and left/right.
  2. For cases shown in Fig 8, there is an open circuit between terminals 1 of connectors A and C if the resistance between terminals 1 of connectors A and C is 10 kΩ or more (open circuit), and the resistance between terminals 2 of connectors A and C is less than 1 Ω.
    
    Fig 8: Measuring Resistance Between ECM Connector Terminals A And C
    Courtesy of SUBARU OF AMERICA, INC.
  3. Disconnect connector B, and measure the resistance between connectors.
  4. For cases shown in Fig 9, there is an open circuit between terminals 1 of connectors B2 and C if the resistance between terminals 1 of connectors A and B1 is less than 1 Ω, and the resistance between terminals 1 of connectors B2 and C is 10 kΩ or more (open circuit).
    
    Fig 9: Measuring Resistance Between ECM Connector Terminals B2 And C
    Courtesy of SUBARU OF AMERICA, INC.
3. Measure the voltage.
  1. A voltage test is performed to check for open circuits in circuits where voltage is applied to ECM connector terminals.
  2. As shown in Fig 10, measure the voltage for ECM 5-V output terminal in the following order with all connectors connected. Between chassis ground and terminals 1 of connector A, connector B, and then connector C.
  3. There is an open circuit in the wire harness circuit between terminals 1 of B and C if the measurement results are as follows.
    
    Fig 10: Measuring Voltage Between ECM Connector Terminals And Chassis Ground
    Courtesy of SUBARU OF AMERICA, INC.
    
    Criteria: Between terminal 1 of connector A and chassis ground: 5 V
    
    Between terminal 1 of connector B and chassis ground: 5 V
    
    Between terminal 1 of connector C and chassis ground: 0 V
Short circuit inspection
1. As shown in Fig 11, a "Ground resistance inspection" is performed if there is a short circuit of a wire harness ground to determine the location of the cause.
  
  Fig 11: Short Circuit Inspection
  Courtesy of SUBARU OF AMERICA, INC.
2. Ground resistance inspection
  1. Disconnect connectors A and C, and measure the resistance between terminals 1 and 2 of connector A, and chassis ground. Standard value: 10 k Ωor more
    NOTE: Measure the resistance while lightly shaking the wire harnesses up/down and left/right.
  2. For cases shown in Fig 12, there is a short circuit between terminals 1 of connectors A and C if the resistance is less than 1 Ω(short circuit) between terminal 1 of connector A and chassis ground, and the resistance between terminal 2 of connector A and chassis ground is 10 kΩ or more.
    
    Fig 12: Ground Resistance Inspection
    Courtesy of SUBARU OF AMERICA, INC.
  3. Disconnect connector B, and measure the resistance between terminal 1 of connector A and chassis ground, and between terminal 1 of connector B2 and chassis ground. There is a short circuit between terminals 1 of connectors B2 and C if the resistance is 10 kΩ or more between terminal 1 of connector A and chassis ground, and the resistance between terminal 1 of connector B2 and chassis ground is less than 1 Ω(short circuit).
    
    Fig 13: Measuring Resistance Between ECM Connector Terminals B2 And C
    Courtesy of SUBARU OF AMERICA, INC.
Visual and contact pressure inspection
1. Disconnect the connectors on both sides.
2. Check that there is no rust or foreign material adhering to the connector terminals.
3. Check that rounded parts are not loose or damaged, and that the terminal is firmly secured in the lock position.
  NOTE: Make sure that the terminal does not release when slightly pulled from the rear.
4. Insert a male test terminal into the female terminal and pull it out.
  NOTE: If it easier to pull out the test terminal in comparison with other terminals, this indicates that the contact of this part is poor.
  
  Fig 14: Pulling Connector Terminal
  Courtesy of SUBARU OF AMERICA, INC.
ECM inspection and replacement
CAUTION:
- With the connector connected to the ECM, check from the rear of the connector on the wire harness side.
- Inspections for which no inspection conditions are indicated, perform with the engine stopped and with IG ON.
1. First test the ECM ground circuit and repair if there is any fault. If normal, it indicates that the ECM is faulty. Replace with a normal ECM and check if there are any malfunction phenomenon present.
  1. Measure the resistance between the ECM ground terminal and chassis ground.
    Standard value: Less than 1 Ω
    
    Fig 15: Checking ECM Ground Circuit (Example)
    Courtesy of SUBARU OF AMERICA, INC.
  2. Disconnect the ECM connector, check that there is no bending of the ground terminals on the ECM and wire harness sides, and measure the contact pressure.
    
    Fig 16: Checking ECM Connector Terminals
    Courtesy of SUBARU OF AMERICA, INC.