Transmission Pressure/Temp Sensor Failure?

[allardiced]

Hi all,

I have a 2021 R29-CB with a Volvo Penta D4-320-IG engine and HS68A-A simple reverse gear transmission. For the past month or so, I have occasionally gotten the following error on my Volvo panel:

Transmission oil temperature sensor failure

I have the Volvo Easy Connect app on my phone connected to the Volvo Easy Connect Gateway device on the boat and therefore I can see the values on the Volvo system, and they are showing very strange values, such as "418" for Transmission Pressure (PSI) and "-4" for Transmission Temp (degrees F).

I suspect the sensor is faulty but how can I verify? And is this an easy item to replace? Or could this be an indication that the cooling system for the transmission is not functioning properly? I believe I found the part # for the sensor (17202573) but do I need to buy the O-ring, adapter, and gasket which are related to it? I believe these are parts # 25 thru 28 on this diagram => https://www.volvopenta.com/shop/0/part-sections/54166033. Is this what is needed to replace the sensor?

Any clarity would be appreciated. I'm concerned there is somethign wrong with the transmission and I won't know it without the working pressure/temperature sensor :/

Regards,
-Darryl
"Little Blue T"

 

[BB marine]

The 418 PSI may be correct but is in the full high range. Normally the pressure tops out at 350 to 400 psi on a ZF reverse gear. The temp seems out of range too. Normal would be ambient when cold and then when warm near engine operating temperature 150 F to 170F. The first troubleshoot item I would preform is confirm good connections. Normally high readings or low readings with sensors are from open circuits or closed circuits. The sensors function by sending a signal of variable resistance. Depending on the design of the sender fully open will be at one end and fully closed at the other end. Poor connections cause fully open readings, bad grounds cause fully open readings. Intermittent readings indicate a circuit that is making and breaking a connection. Confirm all connections are tight and clean. Make sure pin connections are good. If you confirm you have good connections and still have an issue with inconsistent readings then replacing the sensor may be the next easiest troubleshoot. When replacing sensors that use sealing components gaskets, O-rings or seals it is alway a good idea to replace them too. Good luck with your troubleshooting.

 

[allardiced]

Thanks for the thoughts Brian. When in neutral or low idle forward, the PSI says around 411~413, which seems abnormally high, especially in neutral with no force being transmitted thru to the prop. also, the temperature stays around -22F, which is obviously wrong. I have inspected the electrical connections to which I have access, and these seem ok. I suspect pretty strongly that the sensor is faulty and will plan to replace it at our next service interval.

For reference, I believe I will need the following parts, based on this Volvo diagram:
https://www.volvopenta.com/shop/0/part-sections/54166033
25 - gasket
26 - adapter
27 - o-ring
28 - pressure sensor

Does anyone have input regarding if the adapter should be replaced at this same time, or just the Pressure Sensor? Not sure what role the adapter plays. I can check with the service tech when I schedule our service, but would like to be well-informed in advance.

Regards,
-Darryl