Mercury V8 300

• O2 sensor failed
Summary of Fault Correction Possibilities
• Check the O2 sensor fuse. If open, locate the source of the excess current draw. Replace the fuse.
• Inspect the O2 sensor wiring for an open or short, repair as necessary.
• Replace the O2 sensor.
UEGO1_Sensor_Short
Fault Type: Horn: Guardian: UFC: Transmission to Helm: Freeze Frame Priority:
Nonsticky None 100% 821‑27 No 2
Explanation
The oxygen (O2) sensor does not appear to be working properly; the output circuit from the PCM to the O2 sensor is shorted or
has too little resistance.
Possible Causes
• Wiring problem
• O2 sensor failed
Summary of Fault Correction Possibilities
• Inspect the O2 sensor wiring for an open or short, repair as necessary.
• Replace the O2 sensor.
W ..........
Watchdog_Active
Fault Type:
Horn: Guardian: UFC: Transmission to Helm: Freeze Frame Priority:
Nonsticky Critical 5% 4013‑23 Yes 4
Explanation
There is a communication problem with the SmartCraft control system.
Possible Causes
• Internal engine PCM error
Summary of Fault Correction Possibilities
• Replace the PCM.
WaterInFuel_RangeLow
Fault Type:
Horn: Guardian: UFC: Transmission to Helm: Freeze Frame Priority:
Nonsticky Caution 100% 1108‑25 Yes 2
Explanation
The PCM received a signal from the water‑in‑fuel filter that is below the valid limit.
Possible Causes
• Wiring problem
• Defective sensor
• Contaminated fuel
Summary of Fault Correction Possibilities
• Inspect the wiring for problems, repair as needed.
• Replace the sensor.
Fault Codes
Page 4A-46 © 2018 Mercury Marine 90-8M0146617 eng JULY 2018