Notice: Refer to Test Probe Notice in the Preface section.
Important: Circuits which include any solid state control modules, such as the PCM, should only be tested with a 10 megaohm or higher impedance Digital Multimeter.
A Digital Multimeter should be used instead of a test lamp in order to test for voltage in high impedance circuits. While a test lamp shows whether voltage is present, a Digital Multimeter indicates how much voltage is present.
The ohmmeter function on a Digital Multimeter shows how much resistance exists between 2 points along a circuit. Low resistance in a circuit means good continuity.
Important: Disconnect the power feed from the suspect circuit when measuring resistance with a Digital Multimeter. This prevents incorrect readings. Digital Multimeters apply such a small voltage to measure resistance that the presence of voltages can upset a resistance reading.
Diodes and solid state components in a circuit can cause a Digital Multimeter to display a false reading. To find out if a component is affecting a measurement take a reading once, then reverse the leads and take a second reading. If the readings differ the solid state component is affecting the measurement.
Following are examples of the various methods of connecting the Digital Multimeter to the circuit to be tested:
| • | Backprobe both ends of the connector and either hold the leads in place while manipulating the connector or tape the leads to the harness for continuous monitoring while you perform other operations or test driving. Refer to Probing Electrical Connectors. |
| • | Disconnect the harness at both ends of the suspected circuit where it connects either to a component or to other harnesses. |
| • | If the system that is being diagnosed has a specified pinout or breakout box, it may be used in order to simplify connecting the Digital Multimeter to the circuit or for testing multiple circuits quickly. |
