DDEC III/IV Single ECM Troubleshooting – Section 4.5 Use of Digital Volt-Ohm Meter

Section 4.5
Use of Digital Volt-Ohm Meter

Before using this manual, you should be familiar with the digital volt-ohm meter (VOM). You should be able to measure voltage and resistance. You should be familiar with the controls of the meter and how to use it correctly. ‪

For use of a typical digital volt-ohm meter, refer to "4.5.1 Resistance Measurements" , refer to "4.5.2 Continuity Checks" , and refer to "4.5.3 Voltage Measurements" .‪

Section 4.5.1
Resistance Measurements

Perform the following steps to measure resistance:‪

1. Connect the red test lead to the V- Ω (Volt-Ohm) input connector and the black lead to the com input connector on the meter.
2. Set the function/range switch to the desired Ω position. If the magnitude of the resistance is not known, set the switch to the highest range, then reduce until a satisfactory reading is obtained.
3. If the resistance being measured is connected to a circuit, turn off the power to the circuit being tested. Turn off the ignition.
4. Connect the test leads to the circuit being measured. When measuring high resistance, be careful not to contact adjacent points, even if they are insulated. Some insulators have a relatively low insulation resistance which can affect the resulting measurement.
5. Read the resistance value on the digital display.

Section 4.5.2
Continuity Checks

In addition to measuring the specific resistance value of a circuit, some meters will also register if a continuous electrical path exists. If a path exists, the circuit is said to have continuity. (This continuity check can be used in any section of this troubleshooting guide where the test is looking for greater than, less than, or equal to 5 ohms.) An open circuit (broken electrical path) would have ∞ resistance and would not have continuity. To utilize the continuity feature of certain meters:‪

1. Place the function/range switch in any Ω range.
2. Connect the red lead to the V- Ω connector and the black lead to the com connector on the meter. With the test leads separated or measuring an out-of-range resistance, the digital display will indicate OL (over limit) Some meters show "1 +, 1, or ↑."
3. Put one test probe at one end of the wire or circuit to be tested. Use the other test lead to trace the circuit. When continuity is established, an ohm (Ω) symbol will display in the upper left corner of the digital display. If contact in the wire is maintained long enough (about 1/4 second), the OL will disappear and the resistance value of the wire or circuit will display next to the symbol.
4. If your VOM does not work in the manner described above, you must know how your VOM operates in order to use this troubleshooting guide.

Section 4.5.3
Voltage Measurements

Perform the following steps to measure voltage.‪

1. Connect the red test lead to the V- Ω connector and the black lead to the com input on the meter. If a DC-AC switch is present, ensure it is switched to the DC position.
2. Set the function range/switch to the desired volts position. If the magnitude of the voltage is not known, set the switch to a range that will be able to read most voltages seen on a vehicle. Typically, a 20V range will do. Then, reduce the range until a satisfactory reading is obtained.
3. Connect the test leads to the circuit being measured. In the DDEC system diagnostic procedures, voltage measurements are always given as being taken at pins, sockets, battery +, or ground. Following the voltage measurement point, the color test lead to be used is given in parenthesis (red is the V- Ω connection, and black is the com connection). Example: If the procedure displays, "Take voltage reading at socket A3 (red lead) to socket C3 (black lead)", see Figure "Voltage Measurement Hook-up" for the hook-up.
   

   1. Red Lead‪

   2. Black Lead‪

   Figure 1. Voltage Measurement Hook-up