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  1. #1

    MSX 150 ECU Code P135 (O2 Sensor Heater Circuit) HELP!!

    OK all it's been a year and I am still having issues. For a quick recap: My ski was rolled last July and it was overfilled with oil, so oil got into the system and fouled some stuff up. My boost only went about half way up and my max RPM was about 5650. So far I have changed the fuel filter, cleaned out the intercooler, replaced the MAP and BOOST sensors and cleaned the intake where they are attached. I ran the ski and still had the same results. After doing some reading it was said that even if faulty sensors are replaced the ECU codes still need to be cleared to got the ski out of safe mode. This morning I had the codes pulled and it had the following codes: P108 (MAP Sensor Circuit), P113 (Intake air Temp), P130 (O2 Sensor Circuit Error), P135 (O2 Sensor Heater Circuit), P171 (Fuel System), P237 (Boost Pressure Sensor), P243 (Wastegate Selenoid), P1260 (PTO Injector Open), P1263 (Mag Injector Open). The codes were all cleared except for P135 (O2 Sensor Heater Circuit), it would not clear. Shop recommended cleaning it with brakekleen, so i did and ran the ski and still faulty. This time my max RPM is 5050 RPM and still only half boost. I tried disconnecting the O2 sensor and no change. Any more suggestions before trying a new O2 sensor? Thank you all.


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    I don't have a fix for you, but I do have a spare oxygen sensor available;
    O2 oxygen sensor 0451353 for Weber engine (MSX 110, MSX 150)

  3. #3
    desperado's Avatar
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    Quote Originally Posted by rcsscraig View Post
    OK all it's been a year and I am still having issues. For a quick recap: My ski was rolled last July and it was overfilled with oil, so oil got into the system and fouled some stuff up. My boost only went about half way up and my max RPM was about 5650. So far I have changed the fuel filter, cleaned out the intercooler, replaced the MAP and BOOST sensors and cleaned the intake where they are attached. I ran the ski and still had the same results. After doing some reading it was said that even if faulty sensors are replaced the ECU codes still need to be cleared to got the ski out of safe mode. This morning I had the codes pulled and it had the following codes: P108 (MAP Sensor Circuit), P113 (Intake air Temp), P130 (O2 Sensor Circuit Error), P135 (O2 Sensor Heater Circuit), P171 (Fuel System), P237 (Boost Pressure Sensor), P243 (Wastegate Selenoid), P1260 (PTO Injector Open), P1263 (Mag Injector Open). The codes were all cleared except for P135 (O2 Sensor Heater Circuit), it would not clear. Shop recommended cleaning it with brakekleen, so i did and ran the ski and still faulty. This time my max RPM is 5050 RPM and still only half boost. I tried disconnecting the O2 sensor and no change. Any more suggestions before trying a new O2 sensor? Thank you all.
    The O2 sensor is only active at idle and below 4,000rpm. Changing the O2 sensor will not solve your problem.

    The O2 heat sensor circuit is 12vdc + and you need to ensure current flows to the sensor. You need to use a test light to determine if the sensor get both positive and negative current.

    Your rpm limitation is likelly caused by something else. I have corrected a bunch of ECU's that had the same issue with either a code clear with DW or a full reflash to either stock or upgraded calibration. For some reason, some ECU's will not reset properly with a DW code clear and need to be reflashed.

  4. #4
    Desperado, thanks for the reply. I have a couple questions then.
    1. Any ideas on what to look for with the symptoms I mentioned?
    2. Will the P135 ECU code cause it to be in some sort of safe mode?

    Any help you can provide will be greatly appreciated, I am at a major loss here and was really hoping the code clear would have fixed it so I could ride it for the 4th this weekend. What a bummer.

  5. #5

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    Most recently when you were limited to 5050, was the engine warm? The 5650 number is most likely a boost leak. Check intake hoses, clamps, bov, and intake isolator gasket.

  6. #6
    Ride04msx, Yes my engine was warm when it was limited to 5050. Since the codes have been cleared I never reached 5650, in the water anyway. I have not revved it up out of the water to see what the max RPM is. The 5050 is in the water. I rode it for about 10-15 minutes and the RPM's never went above 5050. I am at a complete loss. Any help I can get would be totally amazing. Thank you all.

  7. #7

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    Has it been hot and humid in your area? If boost is not making it into the engine it is basically running as a 750cc 4-stroke N/A motor, not much hp so you will not see much rpm. Like Desperado said, the O2 sensor is not the issue, the engine is running above 4k and the ECM is ignoring it.

    From your above post you have replaced just about every sensor. I believe the most likely cause of your headaches is a boost leak. Here is how you can confirm it: take a pair of vise grips or similar and pinch the hose that connects to the waste-gate actuator mounted on top of the exhaust manifold. Be gentle, you don't want to damage the house. By doing this you have taken control of the turbo away from the ECM. Take the ski out in the water and slowly, I mean slowly, apply throttle. If you go to fast to will trigger an overboost condition (according to service manual rpm will be limited to 4700-4800, it will clear on restart). If this happens or you reach full rpm, then it is not a boost leak. BUT, if you never reach boost and/or full rpm then there is definitely a leak in the intake. I would guess isolator gasket, under throttle body.

  8. #8
    ride04msx, i tried what you said above and I reached a MAX RPM of 5250. So I will start gaining access to the throttle body gasket and give it a shot. Hopefully my local dealer has one in stock. Any tips, tricks or other things I should know while I have all this apart? Thanks a million for your help. Oh Yeah one more thing, not sure if this makes sense or helps troubleshoot but on the trailer out of the water I start the Ski and it reaches about 8200 RPM's. It only seems to be limited RPM's in the water.

  9. #9
    FIXED IT !!!!!! Thank you all for your help !! Well with all your help, I started digging for the Throttle Body Isolator and in the process found one hose clamp missing and one hose almost completely off the turbo because the clamp slipped over the neck. I fixed both of these issues and the ski runs normal once again. Once again thank you all.

  10. #10
    Quote Originally Posted by rcsscraig View Post
    FIXED IT !!!!!! Thank you all for your help !! Well with all your help, I started digging for the Throttle Body Isolator and in the process found one hose clamp missing and one hose almost completely off the turbo because the clamp slipped over the neck. I fixed both of these issues and the ski runs normal once again. Once again thank you all.
    Well not completely fixed. Ran great for a couple hours, then idle started surging from 1650 - 2100 RPM's and WOT would max out at 6000 RPM's. I am thinking maybe I did not get all my oil out of the intercooler. Pulled the MAP and BOOST sensor and they looked clean, no oil to be found. Reinstalled them and still same issues. Now I am stuck again. Closest place to clear my codes with a digitalwrench is 3 hours away. ARGHHH. Any more suggestions?

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