Author Topic: Oil Pressure Switch  (Read 1476 times)

John Demartini

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Oil Pressure Switch
« on: October 25, 2022, 01:13:06 PM »
Good Morbubg:

We recently purchased a 2001 Patriot 40' with 60,000 miles.  There are a few items that need attention, one I found is this pressure switch.  It's located on the curb side frame rail next to the air filter can.  It's rotted away and one of the electrical leads has fallen off; probably what my oil pressure gauge on the dash is pegged at 100psi.  It's a CAT 3126, however the info plaque in the service bay is gone, so I don't have serial numbers. 

Another problem is the engine brake is inop.  Question, could is oil pressure switch be effecting engine brake function? I know they are input interfaces with ECM and TCM .
 Also, can anyone tell me the part number for the oil pressure switch assembly, or the best way to get it?

Joining BAC and access to the forum has been the best decision yet.  I've learned so much and hope to share my knowledge whenever possible.

Thank you,
John & Kathy Demartini
2001 Patriot Princeton 40" Diesel
John Demartini
2000 Patriot Princeton
3126B / 3000 Allison
Toad 2009 CR-V
Demco tow bar
RVi Shadow

Eric Maclean

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Re: Oil Pressure Switch
« Reply #1 on: October 25, 2022, 01:47:57 PM »
John
Your coach actually has 3 oil pressure sending unit s the 2 in your picture are for the gauges one in the dash and one in the service bay.
The third sending unit is actually an oil pressure sensor mounted on the engine and it is the one that the Cat ECM gets it's oil pressure information from ( the Aladin , VMS or Magnum intela drive digital dash readout depending on year of coach  are all being supplied data from the Cat ECM via a serial stream data interface.

If it's you dash gauge that's not working the problem is likely the broken wire at those rear sending units in your picture
The sending units can be picked up at any good parts supply store.

The exhaust brake on your 3126 uses compressed air to operate a valve in the exhaust near the exhaust manifold first check to see if that valve is free and not rusted or stuck.
The valve is operated by a solenoid valve mounted on the top of the upper air tank best accessed by lifting the bed it located on the driver's side on the outside of the frame rail and has a hose which runs over to the valve.
Electrically the valve is operated by a relay controlled by the CAT ECM the system is interfaced with the brake lights and the cruise control relays so that the cruise control will not work with the exhaust brake switch turned on.
For electrical trouble shooting the wiring diagrams in coach assist will help you see how it's wired .
One of the first things to check is brake light function .

Hope this helps
Eric
1997 Patriot Yorktown
3126-B
2009 Chevy HHR
Roadmaster falcon tow bar
Demco Air Force one tow brake.

John Demartini

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Re: Oil Pressure Switch
« Reply #2 on: October 26, 2022, 02:57:34 PM »
Hi Eric:

Thank you for the info and ad advise.  I know the exhaust flapper valve is not stuck, brakes lights work and cruise is functional.  I'll check that air valve you mentioned.

Getting a trans service next week so I might have the shop do the oil pressure senders while it's in.

I'll let you know how it turns out.

Thanks again,

John Demartini
John Demartini
2000 Patriot Princeton
3126B / 3000 Allison
Toad 2009 CR-V
Demco tow bar
RVi Shadow

John Demartini

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Re: Oil Pressure Switch
« Reply #3 on: December 02, 2022, 09:57:28 PM »
Hi Eric:

My local truck center spent some time on the engine brake and came up with the following:

Confirmed exhaust brake inop
Inspected air piston and solenoid - OK
Connected and monitored brake status while running.  Changes to enable.
Activated brake and checked for power at solenoid and had none.
Ground is good.
Supplied power to solenoid and brake applied.
Followed harness, no damage found.
Looked for and could not identify relay but could not find identify due to lack of OEM support.

I know the relays are located in the electrical bay.  I've searched for electrical diagrams in Tech Resource library, but can only find 2002 Patriot and up, no 2001.  Do you think I can trust the 2002 electrical diagram? 

I want to just test/replace the engine brake relay if I can confirm it's location.

Any suggestions or advice is greatly appreciated.

Thank you,

John Demartini
John Demartini
2000 Patriot Princeton
3126B / 3000 Allison
Toad 2009 CR-V
Demco tow bar
RVi Shadow

Eric Maclean

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Re: Oil Pressure Switch
« Reply #4 on: December 03, 2022, 05:15:16 AM »
John
The schematics for a 2002 or even back to 1996 may be close to the same.

The exhaust brake is controlled by the ECM and will only activate above a fixed mph and throttled off
When crushing down the road at speed with the exhaust brake switch turned on say at 50 mph if you take your foot off the throttle the ECM will command the exhaust brake to turn on and at the same time it requests the transmission to shift down to maintain engine RPM to maximize the exhaust brakes effect it continues to down shift as the vehicle slows down until it reaches approximately 10 mph when it shuts off the exhaust brake at any time if you start to throttle back on the exhaust brake will be overriden.

Eric
1997 Patriot Yorktown
3126-B
2009 Chevy HHR
Roadmaster falcon tow bar
Demco Air Force one tow brake.
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