Diagnosing Intermittent Problems; Visual/Physical Check - Mercury V6 175 Diagnostic Manual

2.
If the fault is an Input High or Input Low, refer to the wiring diagram and check each of the leads between the suspect
sensor and the PCM for open and short circuits. Refer to Section 5A ‑ Sensors for information on testing sensors and
circuits. The short circuit does not have to be to ground, it could be to any other wire in the harness.
a. If the leads test good, then the sensor should be replaced. If more than one sensor is affected, look for patterns.
NOTE: When troubleshooting active faults (faults displayed under the View Faults screen), the circuit in question is
experiencing a failure right now. Look for an open circuit or short circuit in the two or three wires involved with the
sensor in question; the sensor itself has actually failed or the connections at the PCM have failed.
b. If the input is high or low for more than one sensor, check the wiring harness for opens or shorts, and eliminate
sensors one at a time by unplugging them to see if the fault clears.
NOTE: When troubleshooting intermittent faults (faults displayed under the Freeze Frame screens or faults that are
not active in the View Faults screen), the circuit in question is not experiencing a failure at this time. Look for an
intermittent connection or an intermittent short circuit that is not present right now. You must still check circuits for
opens and shorts, but you must wiggle wires and connectors during all tests in attempt to locate the poor connection.
Carefully look for subtle problems, such as corroded connections and internal wiring harness splices, and for
connectors with a loose fit between the male and female pins. Ensure that the engine ground connections are clean
and secure.
NOTE: Use the CDS G3 Live Data screen to find intermittent problems. While observing the data from the suspect
circuit, wiggle the wires and connectors (of the suspect circuit) while the key is on or while the engine is running.
When you locate the bad connection or broken or shorted lead, the data reading will fluctuate on the diagnostic tool.
Keep in mind that the refresh rate of the diagnostic tool is relatively slow (every 50 milliseconds or so).
3. If the fault is an abnormal operating condition, repair the system as needed. For example, if the sea‑pump pressure is low,
check the water pickups for obstructions, and then replace the water pump impeller (and other parts as needed). Abnormal
operating condition faults can be active or intermittent.

Diagnosing Intermittent Problems

IMPORTANT: Intermittent problems may or may not cause a fault to be stored.
Most intermittent problems are caused by faulty electrical connections or wiring. Perform a careful visual check for the following
conditions:
• Poor mating of the connector halves or a terminal not fully seated in the connector body.
• Poor terminal‑to‑wire connection (crimping). Remove the terminal from the connector body to check.
All connector terminals in the problem circuit should be carefully checked for proper contact tension.
An intermittent problem may be caused by the following:
• Ignition coil shorted to ground and arcing at ignition wires or plugs.
• Poor PCM grounds, or loose or corroded engine harness ground connections.
• Electrical system interference caused by a sharp electrical surge. Normally, the problem will occur when the faulty
component is operated.
• Improper installation of electrical options such as lights, stereo systems, ship‑to‑shore radios, or sonar.
Digital Multimeter or Diagnostic Tool Use
The vessel may be driven with a digital multimeter connected to a suspected circuit. An abnormal voltage when the malfunction
occurs is a good indication that there is a fault in the circuit being monitored.
A diagnostic tool, such as CDS G3, can be used to help detect intermittent conditions. The diagnostic tool allows manipulation
of wiring harnesses or components with the engine not operating, while observing the diagnostic tool readout. The diagnostic
tool can also be plugged in and observed while operating the vessel.
If the problem seems to be related to certain parameters that can be checked on the diagnostic tool, they should be checked
while operating the vessel. If there does not seem to be any correlation between the problem and a specific circuit, use the
diagnostic tool data to see if there is any change in the readings that might indicate intermittent operation.
The diagnostic tool is also an easy way to compare the operating parameters of a poorly operating engine with those of a
known good one. For example, a sensor may shift in value but not set a fault. Comparing the sensor's readings with those of
the typical diagnostic tool data readings may uncover the problem.
The diagnostic tool has the ability to save time in diagnosis and prevent the replacement of good parts. The key to using the
diagnostic tool successfully lies in the technician's ability to understand the system being diagnosed and the diagnostic tool
operation and limitations. The technician should read the tool manufacturer's operating manual to become familiar with the
tool's operation.

Visual/Physical Check

1. Ensure that the safety lanyard is correctly installed and that the customer understands the correct starting procedure.
2. Verify that the battery is fully charged and is of sufficient capacity for the engine being tested. If necessary, substitute a
known good battery.
90-8M0146617 eng JULY 2018
Troubleshooting with the Computer Diagnostic System (CDS G3)
© 2018 Mercury Marine Page 3B-15