The following precautions will help make the procedures for checking the wiring harnesses easier and safer. Damage can be done to a harness if wires are not hooked up correctly, and the directions for checking the harnesses are written with certain descriptions which stay consistent throughout all of the procedures.
Connector symbols are described as seen from the end of the terminal for the connector.
The abbreviation "B+" used for the normal judgement value when checking the voltage is the abbreviation for battery positive voltage.
Be sure to use the special tool (test harness) when, for a waterproof connector, checking while the circuit is conductive. If a probe is inserted from the harness side, the waterproof capability will be lowered, thereby causing corrosion. Never do so.
Also, if there is no test harness with an applicable connector, the test harness set (MB991348) can be used to make connections directly between the terminals.
When a connector is disconnected in order to check terminal voltage, etc., never insert a probe if the terminal to be checked is a female pin, because the forceful insertion of a probe will cause improper or incomplete contact.
When checking for damaged or disconnected wiring of a harness (open circuit) and if both ends of the harness are unconnected, use a jumper wire to ground one end of the harness, and then check for continuity between the other end and ground. By doing this, you can check for damaged or disconnected wiring, and, if there is no continuity, the harness should be repaired.
When checking for a harness short-circuit (short-circuit to ground), open one end of the harness and then check for continuity between the other end and ground. If there is continuity, the harness is short-circuited to ground and should be repaired.
If the voltage (power-supply voltage) supplied to a sensor is not normal, repair the harness. If the voltage to the sensor is still not normal after the harness has been repaired, replace the engine control unit and check again.