Note whether sensor faults occur singly or if there are multiple failures. The PCM supplies 5‑volt power and ground to the
variety of engine sensors through several circuits and a number of splices. A failed power supply or ground circuit will result in
the appearance of multiple sensor failures. Use the sensor power wiring diagrams to identify which circuits feed power to which
sensors.
To troubleshoot a given sensor circuit:
1. Disconnect the sensor from the engine harness.
2. Perform a visual inspection of the pins at the sensor and the wires coming from the sensor harness connector. Look for
broken, bent, or corroded pins at the sensor and loose, broken, or corroded wires at the connector.
3. Perform a visual inspection of the harness connector at the PCM. Verify that the pins in the harness connector are properly
seated. If the pins are damaged, repair or replace the harness.
4. Inspect the PCM for bent or missing pins. If connectors are damaged, repair or replace the PCM and retest.
Three‑Wire Sensor Power Supply and Ground Circuit Test
IMPORTANT: Wiggle the harness and connector while performing the following tests. If the voltmeter readings vary during the
tests, then a broken, loose, or corroded wire is likely causing the failure. Repair the problematic wire, or replace the engine
harness, and retest the circuit.
IMPORTANT: Turn the key switch to the RUN position, but do not start the engine for the following tests.
DMT 2004 Digital Multimeter
91‑892647A01
1. Measure the voltage between the power supply and ground pins of the engine harness sensor connector. The voltmeter
should read 5 volts. If it does not, continue troubleshooting.
2. Measure the voltage between the power supply pin of the engine harness sensor connector and an engine ground. If the
reading is 5 volts, there is an open in the ground circuit. If there is no voltage, there is either an open voltage supply circuit
or a faulty splice, wire, or connector.
IMPORTANT: Always use appropriate probes, when testing at the engine harness PCM connectors.
3. Check for continuity between the PCM connector and the ground pin at the sensor connector. If the circuit is open, repair
or replace the engine harness and retest.
Terminal Test Probe Kit
Bosch P/N MM‑ 46523
Sensor Signal Circuit Test
DMT 2004 Digital Multimeter
91‑892647A01
IMPORTANT: Always use appropriate probes, when testing at the engine harness PCM connectors.
1. Check for continuity between the signal pin at the PCM connector and the signal pin at the sensor connector.
Terminal Test Probe Kit
Bosch P/N MM‑ 46523
2. Check for continuity to ground from the signal pin.
3. If the circuit is open or grounded, repair or replace the engine harness and retest.
Sensor Opens and Shorts
Two‑Wire Sensor Opens and Shorts
• An open 2‑wire sensor circuit will cause the PCM to read 5 volts on the signal wire.
• A shorted‑to‑ground 2‑wire sensor circuit will cause the PCM to read 0 volts on the signal wire.
• A shorted‑to‑power 2‑wire sensor circuit will cause the PCM to read 5 volts (variable) on the signal wire.
Three‑Wire Sensor Opens and Shorts
Power Lead
• If the power lead opens, the PCM will indicate 0 volts.
• If the power lead shorts to the ground lead or another ground source, the PCM will indicate 0 volts.
• If the power lead shorts to the signal lead or another power source, the PCM will indicate 5 volts.
Ground Lead
• If the ground lead opens, the signal lead will indicate 5 volts.
• If the ground lead shorts to the power lead, the PCM will indicate 0 volts.
Sensors
90-8M0146617 eng JULY 2018 © 2018 Mercury Marine Page 5A-3
To Next Page
Loading...
Need help?
General
