Throttle Position Sensor Troubleshooting Mercury 150 175 200 EFI

  • This troubleshooting information is meant to help trace and correct faults relating to the throttle position sensor on 2000+ Mercury 150 175 200 horsepower EFI engines with a starting serial number of 0T409000 and above.

A throttle position sensor, or TPS, is a device which is used to monitor the air intake of an internal combustion engine. It does this by transmitting throttle angle data to the engine control module (ECM). The ECM then varies the injector pulse accordingly. If the throttle position sensor fails, the warning system will sound an alarm and the ECM will reduce the engine’s RPM. TPS settings can be monitored with the digital diagnostic terminal by way of the ECM but the TPS cannot be adjusted. When powering the engine from idle to wide open throttle the voltage change should occur without erratic behavior. If voltage change is not even or regular in pattern, the TPS is defective.

Location of Throttle Position Sensor TPS, Throttle Stop Screw, Roller and Pocket
(A) Throttle Position Sensor TPS (B) Throttle Stop Screw (C) Roller (D) Pocket

Throttle Position Sensor Specifications

If the throttle position sensor is not within the intended factory operating range when the motor is activated, the ECM will recognize the TPS as being faulty. This will trigger a cascade of events. First an alarm or warning horn will sound, then the check engine light will light up, next the Digital Diagnostic Terminal will indicate that the throttle position sensor has malfunctioned and cause it to reduce the engine’s RPM. When the engine is activated and begins to run, make sure the throttle arm on the Mercury outboard engine is against the throttle stop screw. See image below for throttle arm location. Do not move the fast idle control lever or throttle forward.

Throttle Arm 2002 2003 2004 2005 Mercury Outboard 150hp 175hp 200hp
(E) Throttle Arm

Perform a careful examination to the throttle cable and and make any adjustments if necessary. When examining the throttle stop screw make sure it is against the throttle stop on the cylinder block when the engine is started and running. If it is not resting on the throttle stop, pre-load the throttle cable barrel by rotating it 1 or 2 turns.

Always make sure the driver of the boat is not applying pressure on the throttle (if foot pedal throttle is used) or advancing the throttle on the control box.

Take a close look at the throttle cam to roller adjustment. If the roller (C) is not correctly seated in the pocket/valley (D) area on the cam, there can be an instance where the roller could ride up or down on the cam which could cause the throttle position link arm to pull/push on the throttle position lever  resulting in changing values.

Anyhow. If everything checks out fine and your motor is still experience issues, submit a comment in the comment box below. Provide as much detail as possible and I’ll try and provide an answer.


Hey I am Dennis, an inboard, outboard and sterndrive marine technician with 5+ years of experience. Send me a question using the comment box on this page. If needed, I can post additional advice, diagrams or illustrations to address any question.

11 thoughts on “Throttle Position Sensor Troubleshooting Mercury 150 175 200 EFI

  • Edvin Roev

    Hello Dennis,
    My name is Edvin and lives in Norway.
    I have a Mercury optimax 115, 2014 model.
    I had a problem with starting the motor some times, and more and more often until it wouldn’t start at all. I found a damaged cable from positive + side of the battery. The damaged part of the cable was located under the fuel rack, bottom of casing and wery hard to get access. But anyway I fixed the cable. Now it’s cranking as normal, but not starting. Before I started the work with the cable, I used another cable directly from battery to the starter. It was starting without any problem.
    My question is: why is it not starting now.
    The only thing I have done is to repair the broken cable. Can the ECU been damaged wen working with cable ? The main switch from battery was off during work ( I think )

    Looking forward to your response.
    Regards Edvin

  • Greg jones

    Hey Dennis. Great article!
    I have a 1997 Mercury 225 in SLOW mode. Looking for some guidance. Are you available to connect to discuss?

    • Bill McGraw

      I have a 1999 200 HP EFI Mercury outboard. I started getting an intermittent beep from my alarm while I was out one day. I was a little low in my oil tank. So I refilled the tank but kept getting the alarm. The engine was running perfectly. Good water pressure and temp. After I could not find the issue I drove it back to the dock about five miles watching my gauges. The only thing I could find on line with the intermittent beep was the throttle position sensor. I recently lubricanted my throttle cable. It was getting a little stiff. Any suggestions?

  • Pierre-Yves

    Hello Denis, I have a 150 hp optimax 2004, I have a problem, when the engine is running between 2000 rpm and 3000 rpm, the engine revs automatically as to neutral. I replaced the gas line and all the gas filters and still have the same problem. Do you have an idea? I think it can be tpi! Thank you

  • Lisa Haitz

    Curious, would all this apply to a 2013 90HP? Vesselview app says “ the input sensor is below the valid limit. Throttle position sensor is not working properly”

  • Trying to located TPS on 2008 Merc 50 hp 4 stroke motor. Is it port or starboard side of motor, would love some help to find and change it

  • ray Marasco

    I have a 75hp mercury two stroke engine 2006. My mechanic told me that I need a throttle body sensor. How many hour job is it?

  • Todd Reece

    Hi Dennis,
    I have a 2005 mercury 150xl opt,we have been experiencing a breakdown/stumble/violent miss at higher rpms. The boat starts fine, idles fine and most times will run somewhere between 3800 and 4200 rpm like clock, if we attempt to increase beyond that we experience the above condition. FYI we have been running the boat on a known good portable tank with new fuel lines and bulb to the pulse pump. Any insight is appreciated. Does this sound like a TPS issue?

  • Todd Reece

    My 2005 mercury 150xl opt will start fine, idle fine and run at 3/4 throttle fine. If I attempt to advance to full throttle the engine stumbles/misses and won’t recover until it is re-keyed. Fresh fuel ,new fuel lines,bulb and filter. Do you think this could be a throttle position sensor issue?

  • James Jeffers

    I have a 2018 Mercury 150 4 stroke. When I push the throttle up to running speed, I get 6 beeps and the motor throttles down.

  • Brandon Griffith

    2012 mercury 150 pro xs . Engine won’t run over 4700 RPM at WOT. I tested the TPS sensor and was getting a reading of 4.9VDC at idle. When opened to WOT the reading never changed, but the computer is not throwing a code. Is my TPS sensor bad?


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