MerCruiser Troubleshooting FAQs

Diagnosing EFI Problems

Your authorized Mercury MerCruiser dealer has the proper service tools for diagnosing problems on Electronic Fuel Injection (EFI) Systems. The Electronic Control Module (ECM) on these engines has the ability to detect some problems with the system when they occur, and store a Trouble Code in the ECM's memory. This code can then be read later by a service technician using a special diagnostic tool.

Diagnosing DTS Problems

Your authorized Mercury MerCruiser dealer has the proper service tools for diagnosing problems on Digital Throttle & Shift (DTS) Systems. The Electronic Control Module (ECM)/Propulsion Control Module (PCM) on these engines has the ability to detect some problems with the system when they occur, and store a Trouble Code in the ECM/PCM's memory. This code can then be read later by a service technician using a special diagnostic tool

Additional Operation Instructions for Axius Systems

If your boat has DTS engines equipped with an Axius system, refer also to the Axius Operation Manual included with the boat.

Engine Guardian System?

The Engine Guardian System monitors the critical sensors on the engine for any early indications of problems. The system will respond to a problem by emitting a continuous beep and/or reducing engine power in order to provide engine protection. If Guardian System has been activated, reduce throttle speed. The horn will turn off when throttle speed is within the allowable limit. Consult an authorized Mercury MerCruiser dealer for assistance.

Starter Motor Will Not Crank Engine, or Cranks Slowly?

Possible Cause Remedy
Battery switch turned off. Turn the switch on.
Remote control not in neutral position. Position the control lever in neutral.
Open circuit breaker or fuse. Check and reset the main power circuit breaker or replace the fuse. Check the 5 amp fuse on the power harness connected to the battery, and replace if necessary
Loose or dirty electrical connections or damaged wiring. Check all electrical connections and wires (especially battery cables). Clean and tighten all faulty connections.
Bad battery or low battery voltage. Test the battery and charge if necessary; replace if bad.
Lanyard stop switch activated. Check the lanyard stop switch.

Engine Will Not Start or Is Hard to Start?

Possible Cause Remedy
Lanyard stop switch activated. Check the lanyard stop switch.
Improper starting procedure. Read the starting procedure.
Insufficient fuel supply. Fill fuel tank or open valve.
Faulty ignition system component. Service the ignition system.
Clogged fuel filter. Replace fuel filter.
Stale or contaminated fuel. Drain fuel tank. Fill with fresh fuel.
Fuel line or tank vent line kinked or clogged. Replace kinked lines or blow out lines with compressed air to remove obstruction.
Faulty wire connections. Check wire connections.
EFI system fault. Have EFI System checked by an authorized Mercury MerCruiser dealer.

Engine Runs Rough, Misses, or Backfires?

Possible Cause Remedy
Clogged fuel filter. Replace filter.
Stale or contaminated fuel. If contaminated, drain tank. Fill with fresh fuel.
Kinked or clogged fuel line or fuel tank vent line. Replace kinked lines or blow out lines with compressed air to remove obstruction.
Flame Arrestor dirty. Clean Flame Arrestor.
Faulty ignition system component. Service ignition system.
Idle speed too low. Have EFI system checked by an authorized Mercury MerCruiser dealer.
EFI System fault. Have EFI System checked by an authorized Mercury MerCruiser dealer.

Poor Performance?

Possible Cause Remedy
Throttle not fully open. Inspect the throttle cable and linkages for proper operation.
Damaged or improper propeller. Replace the propeller.
Excessive bilge water. Drain and check for cause of entry.
Boat overloaded or load improperly distributed. Reduce load or redistribute load more evenly.
Flame arrestor dirty. Clean the flame arrestor.
Boat bottom fouled or damaged. Clean or repair as necessary.
Ignition problem. See Engine Runs Rough, Misses or Backfires.
Engine overheating. See Excessive Engine Temperature.
EFI System fault Have EFI System checked by an authorized Mercury MerCruiser dealer

Excessive Engine Temperature?

Possible Cause Remedy
Water inlet or seacock closed. Open.
Drive belt loose or in poor condition. Replace or adjust belt.
Seawater pickups or sea strainer obstructed. Remove obstruction.
Faulty thermostat. Replace.
Coolant level (if equipped) low in closed cooling section. Check for cause of low coolant level and repair. Fill system with proper coolant solution.
Heat Exchanger or Fluid Cooler plugged with foreign material Clean Heat Exchanger, Engine Oil Cooler, and Transmission Oil Cooler (if equipped).
Loss of pressure in closed cooling section. Check for leaks. Clean, inspect and test pressure cap.
Faulty seawater pickup pump. Repair.
Seawater discharge restricted or plugged. Clean exhaust elbows.

Insufficient Engine Temperature?

Possible Cause Remedy
Faulty thermostat. Replace.

Low Engine Oil Pressure?

Possible Cause Remedy
Insufficient oil in crankcase. Check and add oil.
Excessive oil in crankcase (causing it to become aerated). Check and remove required amount of oil. Check for cause of excessive oil (improper filling).
Diluted or improper viscosity oil. Change oil and oil filter, using correct grade and viscosity oil. Determine cause for dilution (excessive idling).

Battery Will Not Recharge?

Possible Cause Remedy
Excessive current draw from battery. Turn off non‑essential accessories.
Alternator drive belt loose or in poor condition. Replace and/or adjust.
Unacceptable battery condition. Test battery, replace if necessary.
Loose or dirty electrical connections or damaged wiring. Check all associated electrical connections and wires (especiallybattery cables). Clean and tighten faulty connections. Repair or replace damaged wiring.
Faulty alternator Test alternator output, replace if necessary.

Remote Control Is Difficult to Move, Has Excessive Play, or Makes Unusual Sounds?

Possible Cause Remedy
Insufficient lubrication on shift and throttle linkage fasteners. Lubricate.
Obstruction in shift or throttle linkages. Obstruction in shift or throttle linkages.
Loose or missing shift and throttle linkages. Check all throttle linkages. If any are loose or missing, see authorized Mercury MerCruiser dealer immediately
Shift or throttle cable kinked. Straighten cable or have authorized Mercury MerCruiser dealer replace cable if damaged beyond repair.

Steering Wheel Jerks or Is Difficult to Turn?

Possible Cause Remedy
Low power steering pump fluid level. Check for leak. Refill system with fluid.
Drive belt loose or in poor condition. Replace and/or adjust.
Insufficient lubrication on steering components. Lubricate.
Loose or missing steering fasteners or parts. Check all parts and fasteners if any are loose or missing, see authorized Mercury MerCruiser dealer immediately.
Contaminated power steering fluid. See authorized Mercury MerCruiser dealer.

Power Trim Does Not Operate (Motor Does Not Operate)?

Possible Cause Remedy
Blown fuse. Replace fuse. Fuses may be located near the dash trim switch, at the trim pump, in the positive (red) power trim battery lead near the battery switch, or a combination of these.
Loose or dirty electrical connections or damaged wiring Check all associated electrical connections and wires (especially battery cables). Clean and tighten faulty connection. Repair or replace wiring.

Power Trim Does Not Operate (Motor Operates but Sterndrive Unit Does Not Move)?

Possible Cause Remedy
Trim pump oil level low. Fill pump with oil.
Drive unit binding in gimbal ring. Check for obstruction.