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Clayton
Clayton, Mechanic
Category: Heavy Equipment
Satisfied Customers: 755
Experience:  5+ Years at Freightliner, Detroit & MBE Certified, ATD, and Electrical
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Freightliner..an intermittent problem..oil pressure gauge..rises

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I have a 2005 Freightliner M2 Business class truck. I have an intermittent problem with the oil pressure gauge failing the pre-start tests. Occasionally in the pre-start test, it rises up, falls down, then goes back up. Then when I attempt to start it, it reads no oil pressure so the Engine Protect warning light comes on and it shuts down after a few seconds. How do I test and replace the sensor if needed?
Chat Conversation Started
Clayton :

Hi, Welcome to Just Answer

Clayton :

Hello

Clayton :

I have some questions to ask you

Customer:

OK

Customer:

I am wondering if that oil pressure sensor is on a relay.

Clayton :

Oil pressure sensor is not on a relay.

Clayton :

your guages sweep with the key on, engine off fine?

Customer:

OK, it is failing the pre-test before the engine is started.

Clayton :

If it fails the pre-test, then the only problem it has to be is the instrument cluster

Customer:

The others do, but occasionially the oil pressure guage sweeps, goes to zero then back up. This is a sure sign it has failed the test.

Clayton :

so the oil pressure guage goes back up with the key on, but engine off?

Customer:

If it stays on zero before starting, it is good, then engine will start fine and the 'Engine Protect' warning will not come on.

Customer:

Yes

Clayton :

what does it go up to when it acts up

Customer:

It goes all the way up. Normally, it sweeps up, then back done to zero before starting.

Clayton :

Alright, your oil pressure gets its signal through J1939 from the engine ECM. By any chance you have another truck just like this one?

Customer:

No, the only one. I use it for farming, hay hauling with a trailer.

Clayton :

I will venture to say the instrument cluster is causing this problem. So the oil pressure guage is pegging out to 100?

Customer:

There are a couple of plugs going into the fuse box assembly. They had gotten oily and I cleaned them out with DD40. Seemed to help, but I think it was coincidental. Yes, the oil pressure guage pegs out to the max.

Customer:

This has happened several times, then it goes back to normal for a while.

Customer:

When it is running fine, the oil pressure guage works fine.

Clayton :

Two possibilties, the oil pressure sensor is acting up, maybe a shorted wire, or the instrument cluster is at fault.

Customer:

Where is the oil pressure sensor and where does the sense wire go?

Clayton :

I wish you had access to the right program to monitor oil pressure through the engine ecm to confirm this

Clayton :

You have a MBE 900?, Cat?, or Cummins?

Customer:

I know that the oil pressure is actually good. If it fails the pre-test sweep, it will not sense oil pressure. It is a C7 Cat.

Clayton :

thats why it has me thinking it is the cluster. The instrument cluster sweeps regardless of what the engine is doing

Customer:

If I try to start it after it fails the sweep, the engine will start but the 'Engine Protect' light will come on and shut the engine down.

Clayton :

does the guage sweep to max then stay, or sweep to max, come back to zero, then sweep back to max

Customer:

Yes, but it is not sweeping properly. All the other instruments sweep up, then back down and stay down. The oil pressure guage sweeps up, back down, then goes back up to max.

Customer:

Sweeps to max, goes back down, then goes back up to max.

Clayton :

what is your engine serial number, I can get you the location of the oil pressure sensor, but I honestly do not think it is your problem

Customer:

Sorry, I don't know the serial number. It is a 2005 Cat C7 engine.

Clayton :

let me see what I can dig up

Customer:

There must be some check that it is doing on the oil pressure sensor, or communication it is attempting with the sensor during the sweep test.

Customer:

It seems to be failing to communicate with the sensor, or the sensor is intermittent.

Clayton :

during the sweep no communication is occuring, this tests basically tests all guages and lights. Helps weed out problems

Clayton :

like if one guage cycles like the tach, but the speedo does not...pretty much concludes the speedo is faulty

Customer:

I see, then why does it sweep back up?

Customer:

The guage is sweeping.

Customer:

Why would it sweep back up, what is that supposed to be saying\?

Clayton :

since it is doing the test sweep completely is making me think faulty sensor or wiring,, if it sweeped, then stayed, then I would be 100 percent s ure it is the cluster.

Customer:

Yes, it could be a faulty wire or sensor. Do you know how I access the sensor?

Clayton :

I would love to have your Engine serial number, I am looking at a picture of a c7, unknown yr, and it says it is located on the driver side of the engine, between the ECM and the fuel pump, on the side of the block

Customer:

I could see if I could find it. Where on the engine would the serial number be? I have to go out with a flashlight.

Clayton :

On the valve cover, or the Engine ECU. If I had the last 6 digits of your VIN, I can get it that way

Customer:

OK, give me a few minutes.

Clayton :

ok

Customer:

ok, I'm still here, the coyotes didn't get me. Last six digits of the VIN are U83008. I think the engine serial number off the ECM is 159998, but I'm not sure that's it. It also had a number of U83008, so I think that is it.

Clayton :

okay, let me see

Clayton :

remember this number. KAL57835

Clayton :

that is your engine serial number

Customer:

OK

Clayton :

Oh, your truck has open recalls.

Customer:

OK

Clayton :

oil pressure sensor is on the driver side, between the Engine ECM, and the fuel pump

Customer:

On the block?

Clayton :

right behind the blowby tube

Clayton :

yea

Clayton :

to the left of the engine ecm, appears to be right next to it

Customer:

It unscrews from the block?

Clayton :

ya, most likely

Customer:

Do you know how I can get a diagram?

Clayton :

a wiring diagram?

Customer:

No, just a sketch of the sensor on the block.

Clayton :

Ya..be right back

Customer:

OK, a wiring diagram would be good as well so I can trace the wiring.

Clayton :

Click here

Customer:

I actually think I know where the two wires come out - into a plug that goes into the fuse box.

Clayton :

they should not go to a fuse box, they go straight to the Engine ECM

Customer:

OK

Customer:

That sensor should test with an ohmeter?

Clayton :

ya. I would wiggle wires in the harness and see if the guages bounce around

Clayton :

also

Customer:

OK, you've been really helpful. Thanks for the PDF which I saved. I'll give it a try in the morning.

Clayton :

Alright, No problem

Clayton and other Heavy Equipment Specialists are ready to help you
Thanks for choosing JustAnswer, I am glad we are able to help you
Customer: replied 6 years ago.

Clayton, I went to the link for feedback. It does not allow me to enter any feedback at this time. In any event, you did a great job helping me out and it did help me to solve the issue. Angus Tocher

That is good to hear, Just check back often to see if feedback is availiable