630 oil temp and charge pressure sensors

[Retired Don]

I've been chasing some issues in a previous thread but now have a more specific question that I think merits a separate thread. I had a "flickering" Trans Oil warning light when I was operating my 630 last week. With help from folks here I have cleaned the sintered bronze filter and totally cleaned the port block. However what I have learned in the process that my old machine doesn't have a charge pressure sensor mounted on it any longer. Must have caused someone an issue in the past. Therefore my flickering light is most likely some other electrical problem. Now I'm trying to understand the circuil that includes these sensors. When I ohmed out the wiring, I found that both leads going to the temp and pressure sensors are common. I noted that at least my temp sensor measures as an "open" to ground in the cold state. I also measured about 20 ohms from each of the sensor leads to ground. Does that sound right? If yes, I'm having trouble understanding just how the circuit operates. I would assume that the sensors would provide a ground when they exceed the limit, but putting a ground on a circuit that currenly only has 20 ohms to ground already doesn't make a lot of sense to me. Can anyone shed some light on this for me? Oh, and any suggestions on a good place to buy a new pressure sensor reasonably? Thanks

 

[Tazza]

The light should be connected to the oil temperature sender, not engine. The enging oil pressure switch should have a light on it's own, the other is charge pressure/temperature.
The sender should have been screwed into that square block you are tackling, they leak over time, that's probably why it was removed and plugged off.

 

[Retired Don]

The light should be connected to the oil temperature sender, not engine. The enging oil pressure switch should have a light on it's own, the other is charge pressure/temperature.
The sender should have been screwed into that square block you are tackling, they leak over time, that's probably why it was removed and plugged off.

That is the way I understand it too. The flickering light I had that started everything was on the Transmission oil light, not the engine oil light. As I understand it either sensor on the port block could trigger that Tranny light, but in my case now I only have the option of getting a signal from the temperature sensor seeing the other wire is just hanging there. What I don't understand is just what happens in the circuit when something happens and the light is supposed to get turned on, for example the hydraulic oil gets too hot. I would have guess that the sensor would go from a normally open to a closed condition and then provide a ground so that current could pass through the light and turn it on. But, I would also have guessed that if that was the case I would have measured a much higher resistance than the approximate 22 ohms that I measured on the sensor wire (when disconnected from sensor) to ground.

 

[mahans7]

That is the way I understand it too. The flickering light I had that started everything was on the Transmission oil light, not the engine oil light. As I understand it either sensor on the port block could trigger that Tranny light, but in my case now I only have the option of getting a signal from the temperature sensor seeing the other wire is just hanging there. What I don't understand is just what happens in the circuit when something happens and the light is supposed to get turned on, for example the hydraulic oil gets too hot. I would have guess that the sensor would go from a normally open to a closed condition and then provide a ground so that current could pass through the light and turn it on. But, I would also have guessed that if that was the case I would have measured a much higher resistance than the approximate 22 ohms that I measured on the sensor wire (when disconnected from sensor) to ground.

It sounds like whatever your sensor wire is connected to before ground may be partially shorted. Can you explain again what it is connected to?

 

[Retired Don]

It sounds like whatever your sensor wire is connected to before ground may be partially shorted. Can you explain again what it is connected to?

Well, maybe I'm not as bad off as I thought. Today I did another check which I should have done at the same time I was "ohming things out". That is I turned the key on and checked the voltage at each of the disconnected sensor wires. I read battery voltage. Then when I grounded either of them my Trans Warning light lit up like it should have. Perhaps my problem was really that the loose pressure sensor light might have been bumping something and causing the warning light to flicker. Maybe I just don't need to really understand the circuit as of yet. So, I think I am ready to get a new pressure switch and install it and give the whole thing another try (after I complete the other things I have underway too). Seeing I believe this will be the first Bobcat part I will have purchased, is there a recommended economical source at which to shop? Thanks Don

 

[SkidRoe]

Well, maybe I'm not as bad off as I thought. Today I did another check which I should have done at the same time I was "ohming things out". That is I turned the key on and checked the voltage at each of the disconnected sensor wires. I read battery voltage. Then when I grounded either of them my Trans Warning light lit up like it should have. Perhaps my problem was really that the loose pressure sensor light might have been bumping something and causing the warning light to flicker. Maybe I just don't need to really understand the circuit as of yet. So, I think I am ready to get a new pressure switch and install it and give the whole thing another try (after I complete the other things I have underway too). Seeing I believe this will be the first Bobcat part I will have purchased, is there a recommended economical source at which to shop? Thanks Don

LPS may carry it, otherwise, check with your dealer - they have a habit of surprising you from time to time.

 

[SkidRoe]

LPS may carry it, otherwise, check with your dealer - they have a habit of surprising you from time to time.

And there is always eBay....

 

[mrdeere1959]

And there is always eBay....

6557449 SWITCH hydraulic pressure $ 38.78

 

[Retired Don]

6557449 SWITCH hydraulic pressure $ 38.78

Thanks for the help guys - I can go shopping now.

 

[Retired Don]

Thanks for the help guys - I can go shopping now.

Hey I found a sensor on Ebay that is listed for use on lots of newer model Bobcats. the P/N listed was 6665371, does anyone know if that is interchangeable with the 6557449 listed above in the thread? It is listed for $25.