M45 V8-4.5L (VK45DE) (2006)
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The continuity check is used to find an open in the circuit. The Digital Multimeter (DMM) set on the resistance function will indicate an open circuit as
over limit (no beep tone or no ohms symbol). Make sure to always start with the DMM at the highest resistance level.
To help in understanding the diagnosis of open circuits please refer to the schematic.
1. Disconnect the battery negative cable.
2. Start at one end of the circuit and work your way to the other end. (At the fuse block in this example)
3. Connect one probe of the DMM to the fuse block terminal on the load side.
4. Connect the other probe to the fuse block (power) side of SW1. Little or no resistance will indicate that portion of the circuit has good continuity.
If there were an open in the circuit the DMM would indicate an over limit or infinite resistance condition. (point A)
5. Connect the probes between SW1 and the relay. Little or no resistance will indicate that portion of the circuit has good continuity. If there were an
open in the circuit the DMM would indicate an over limit or infinite resistance condition. (point B)
6. Connect the probes between the relay and the solenoid. Little or no resistance will indicate that portion of the circuit has good continuity. If there
were an open in the circuit the DMM would indicate an over limit or infinite resistance condition. (point C)
Any circuit can be diagnosed using the approach in the example.
Voltage Check Method
To help in understanding the diagnosis of open circuits please refer to the previous schematic.
In any powered circuit an open can be found by methodically checking the system for the presence of voltage. This is done by switching the DMM to the
voltage function.
1. Connect one probe of the DMM to a known-good ground.
2. Begin probing at one end of the circuit and work your way to the other end.
3. With SW1 open probe at SW1 to check for voltage.
4. With SW1 closed relay and solenoid disconnected and the DMM leads across both fuse terminals check for voltage.
voltage; short is between SW1 and the relay (point B).
no voltage; short is further down the circuit than the relay.
5. With SW1 closed relay contacts jumped with fused jumper wire check for voltage.
voltage; short is down the circuit of the relay or between the relay and the disconnected solenoid (point C).
no voltage; retrace steps and check power to fuse block.
Any powered circuit can be diagnosed using the approach in the example.
TESTING FOR "SHORTS" IN THE CIRCUIT
To simplify the discussion of shorts in the system please refer to the schematic.
Resistance Check Method
1. Disconnect the battery negative cable and remove the blown fuse.
2. Disconnect all loads (SW1 open relay disconnected and solenoid disconnected) powered through the fuse.
3. Connect one probe of the ohmmeter to the load side of the fuse terminal. Connect the other probe to a known-good ground.
4. With SW1 open check for continuity.
continuity; short is between fuse terminal and SW1 (point A).
no continuity; short is further down the circuit than SW1.
5. Close SW1 and disconnect the relay. Put probes at the load side of fuse terminal and a known-good ground. Then check for continuity.
continuity; short is between SW1 and the relay (point B).
no continuity; short is further down the circuit than the relay.
6. Close SW1 and jump the relay contacts with jumper wire. Put probes at the load side of fuse terminal and a known-good ground. Then check for
continuity.
continuity; short is between relay and solenoid (point C).
no continuity; check solenoid retrace steps.