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Cat Sensor Error

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Got this error recently:


SPN 65671 CM 0

Data Valid but below normal rng



Got the same reading for both Cat_A and Cat_B sensor (which I am pretty sure means both sides). Would anyone have any guidance? Our lake has been shallow lately and I have had to unclog the intake screen a few times. Could this be a related to cooling issues?

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Is your boat a 2008 model?

Indmar had an issue with the cat sensors during that time frame and most folks had to by-pass the sensor with a resistor per Indmar suggestion. It was common for both Malibu and Mastercraft models of that era.

If you can’t find anything on it, let me know and I’ll see if I can dig up the information that Indmar sent me.



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Posted (edited)

If you did not get an audible / visual alarm at the helm and no engine power derate, then don't worry about it.  The recommended ECM recalibration prevents that code from causing an alarm or power reduction.  If you do get an alarm or power reduction there are two ways to take care of it.

The engine ECM calibration can be updated, or the cat temperature sensor harnesses can be cut and a 470 ohm resistor wired in place of the sensor.

Edited by csleaver
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Posted (edited)

Thanks for the replies. Yes it is a '08 VTX with a Monsoon 340 engine. Some googlefu revealed this issue and I think this is what is happening. The weird thing is that per my memory the post cat temp sensor is already clipped. I will verify that the circuit is bypassed with a resistor. There is no audible alarm. Maybe some current fluctuations tripped an error code that is erroneous (since the cat temp sensor isn't really used)? I can't really think of anything else. Are there any other major issues that this could indicate? It seems weird for an error code to pop up even if it is already bypassed but I can't think of any reason to not use the boat at this point.

Edited by LateNightSalami
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