Working Practice With A DVOM

Working Practice With A DVOM

Observe the following practices when using a DVOM for engine management diagnostic purposes.

Breaking And Making ECM Connections
Always switch the ignition OFF before breaking or making the BCM connections.

Resistance Measurement
Before taking a resistance measurement, disconnect the component or the vehicle battery. Even a very low quiescent current will result in an incorrect resistance measurement.

Ground Connection Resistance
The ground connection resistance from a component to a known good chassis ground point should be less than 1 ohm.

Voltage Measurements
Voltage measurements are made with the DVOM negative probe connected to a known good chassis ground point, unless noted otherwise.

Back Probe When Making Voltage Measurements
When making voltage measurements, do not disconnect components unless noted otherwise. Instead, back probe terminals while they are still connected to the components.

To "back probe" a connector, first pull back the connector cover (if present). Then, insert the DVOM measurement probe into the backside of the terminal block until the probe touches the terminal pin. In a terminal pin is difficult to reach, switch the ignition OFF, unplug the connector and insert the probe to the backside of the terminal block until the probe touches the terminal pin. Then, plug in the connector. A bent paper clip can reach a terminal pin in a tight area. Switch the ignition ON and take the voltage measurement

CAUTION: Do not probe through wire to connector seals or through wire insulation. Doing so may damage the conductor and/or cause corrosion damage at a later date.

Inspecting Connectors
When inspecting block type connectors, unplug the connector and carefully inspect for pins that are bent, pushed back, corroded or spread open. Remove suspect terminals from the connector block for closer inspection.

Inadvertent DTC Flagging
If components are disconnected when the ignition is ON, a DTC may be inadvertently flagged.