Diagnostic Service Probe

IMPORTANT:
^ Diagnostic service probes are for use on .35, .50 and .80 mm (22, 20 and 18 gage) wires only.
^ The diagnostic service probes must be left on the wire after use. The probe contains a sealant that will protect the wire from corrosion. Do not remove the diagnostic service probe after use.

The use of the diagnostic service probe offers many advantages in system diagnostics over the old jumper wire and terminal back-probe methods. The most important advantage of the diagnostic service probe method of diagnostics is the ability to observe the operation of a circuit without disturbing the components or connections. This is an important advantage since many circuit failures are vibration or connection related. The diagnostic service probe is designed to firmly hold multimeter test probes to allow more accurate readings while the circuit is operating. Circuits with bad connectors, grounds, or components are easier to diagnose while they are operating.

Attach the diagnostic service probe to the wire leading to the connector and insert your multimeter into the diagnostic service probe. Put the meter on the appropriate scale and observe the readings. If the readings do not compare with the expected readings, gently wiggle the wire back and forth in the connector.

If the reading on the meter changes while you are wiggling the wire, the terminal or connector is faulty. Disconnect the connector and examine the terminals and connector cavities for damage. Check the terminals to see if a known good terminal makes a firm connection. Do this by inserting a known good male terminal into the female terminal you are testing. The male terminal should be held firmly in place by the female terminal and should not be loose enough to fall out if the female terminal is held downward. Likewise, test a male terminal by inserting it into a known good female terminal. The two terminals should fit snugly together and should not separate if the male terminal is held vertically downward. If the connections are good (both wire connections and the connection to the component), check the ground connection. Attach a diagnostic service probe to the ground side of the circuit or component. Place a multimeter probe in the diagnostic service probe and the other probe to a known good ground.

NOTE: Check the accuracy of the multimeter first by touching the leads together. The meter should read less than 0.10 ohm with the leads touching.

Place the multimeter on the lowest ohmmeter scale. The meter should read less than one ohm. If the meter reads more than one ohm, check the connections to the ground splice pack (if applicable) or check the ground attachment point. Attach a jumper wire from the ground attachment ring terminal. Attach it to the ring terminal without moving or disturbing the terminal fastener. This can be done by attaching the jumper wire to the crimp lead part of the ring terminal. Attach the other end of the jumper wire to a known good ground and watch the multimeter to see if the reading goes below one ohm. If the reading goes below one ohm, remove the ground screw or nut, clean the connection surfaces and install. If the reading stays above one ohm, check for an open in the ground wire. Also check for continuity from the component to the diagnostic service probe.

Other uses for the diagnostic service probe:
^ Compare voltage readings across connectors, components, or lengths of wire. This allows you to observe the operation of a circuit without the addition of jumper wires or back-probing connections. The best time to diagnose most circuits is while they are operating.
^ Observe changing voltages and compare them to what the PCM is reporting. This can be done by comparing the voltage readings of the PCM inputs to the reported PCM readings displayed on the scan tool or the service stall system (SSS). This can help detect damaged or faulty PCM connections, or a faulty PCM.

IMPORTANT: There are differences between the actual voltages from the sensors and the reported voltages by the PCM. This is due to the internal conversion of these voltages to binary data by the PCM. However, the voltages should generally vary together and the difference should be less than 0.2 volt.

^ The diagnostic service probe can be used with future test equipment to gain access to a circuit for testing or calibration.
^ The diagnostic service probe can be used to give a good ground access point. Attach a diagnostic service probe to a ground circuit and insert the multimeter lead in the probe at a ground reference. Check the ground circuit to verify the ground path is good.