Why there is no voltage at the oil-pressure-sender terminals??!!

[kayooh]

Hello Group,
I have a 92 600SEL w/ approx 126,000 miles. the car shows very little oil pressure (if at all) at any speed. On very rare occasions it may go up to 1/2 bar and on at least one occasion it went to 1 bar.
My suspicions focused on a bad oil pressure sender and when I finally got around to doing the inspection, there was no voltage at all at the terminals which go on the sender!!
Does any body know why there is no oil pressure and why there is no voltage at the oil pressure sender terminals?

Thank you all.

[MikeTangas]

Because you check the sender by reading resistance (ohms).

[myarmar]

You need to run Instrument cluster function test. To do it start engine, then press small button in the center of clock adjusting knob (not the knob itself) for more then 5 seconds. You'll need something like a sharp pencil to do it.
The first test will appear on the outside temperature display. It will read something like 35.1, were 35 is gas in the tank in liters and 1 is the number of the test. To advance to the next step pull the clock knob and turn it clockwise.
There are 9 steps:
1. Gas in the tank in liters
2. Momentary fuel consumption 34.2 is 3.4 liters per hour 2 is step number
3. Engine oil pressure in bar 20.3 means 2.0 bar step 3
4. Engine rpm x 1000
5. Engine oil level 0.5 is OK, 1.5 not OK
6. Activation of the oil pressure, fuel consumption, and fuel tank gauges - needles in the first quarteer of the dial. Indicator 0.6 for step 6
7. Activation of the oil pressure, fuel consumption, and fuel tank gauges - needles in the second quarteer of the dial. Indicator 0.7 for step 7
8. Activation of the fuel consumption, and fuel tank gauges - needles in the third quarteer of the dial. Oil pressure gauge stays in the second quarter. Indicator 0.8 for step 8
9. Activation of the fuel tank gauge, needle in the fourth quarter of the dial, oil pressure remains in the second qurter, fuel consumption remains in the third quarter. Indicator 0.9 for step 9
Done
You need to verify oil pressure reading in step 3 and gauge in steps 6...9
Good luck, Mike

[myarmar]

Originally posted by MikeTangas
Because you check the sender by reading resistance (ohms).

And here are the readings:
13 ohm - 0 bar
40 ohm - 1 bar
90 ohm - 2 bar
150 ohm - 3 bar

[kayooh]

Myarmar,
Thanks for a most informative reply. I'll try it first thing in the morning. Maybe I should do it right now!! I guess I should wake the mrs as soon as I post this.

Mike,
I am also thankful for the quick reply and to the fact that your reply enticed myarmar to post resistance readings for the sender which I would have needed as soon as I figure why there is no voltage in the wire going to the sender.

I had tried in my original post, to make it clear that I was talking about the absence of voltage in the terminals at the end of the wire which is connected to the sender, NOT the terminals on the sender itself. Apparently I failed to make that issue clear enough.

Thanks to both of you for your valued help, I truly appreciate it.

[dpetryk]

There is always some voltage present on the sensor when it is connected to the instrument circuits. By definition there must be. Mike is right, there is no volgate generated by the sensor itself. So if you are not reading anything, then I would say the problem is most likely in the circuit connected to the sensor.

[kayooh]

Myarmar and others,
I was extremely excited to attempt your suggested test but the outside temperature display is not functioning and has not been for a while.
It looks like I should take care of the display before proceeding with the instrument test??

Any suggestions on this one too?

Interestingly enough though, pushing the center of the clock knob for a few seconds initiates (on the trip odometer) a sequence similar to the one you describe but not quite (If I am not mistaken, it does not cycle through as many steps as in the test you had suggested but most of the numbers displayed are preceded by the a "-", most probably meaning a negative value which does not seem to be logical!!).

Do you know what this sequence is?

Any input will be appreciated.

Thank you.

[myarmar]

OK, the procedure was for the cluster with mechanical odometer. You have newer cluster and the procedure is different. Test steps and values are displayed in the odometer window.
To activate test mode start engine and then press small button in the center of clock adjusting knob (not the knob itself) for more then 5 seconds. The odometer display will show "---------". Within 5 seconds pull and turn clockwise clock knob. The first test displayed in the odometer window as "1 80". The trip odo window showes SE for the standard US fuel tank. To go to the next step pull and turn the knob again. There are same 9 steps as with the old cluster. The display will show test step number on the left and result on the right. Decimal point is represented by _.
1. Gas in the tank in liters 1 80
2. Momentary fuel consumption 2 3_4 is 3.4 liters per hour 2 is step number
3. Engine oil pressure in bar 3 2_0 means 2.0 bar step 3
4. Engine rpm 4 2200
5. Engine oil level 5 0 is OK, 5 1 not OK
6. Activation of the oil pressure, fuel consumption, and fuel tank gauges as well as speedometer and tachometer - needles in the first quarteer of the dial. Indicator 6 3_7 for step 6 and 3.7 kOhm outside temp sensor resistance.
7. Activation of the oil pressure, fuel consumption, and fuel tank gauges as well as speedometer and tachometer- needles in the second quarteer of the dial. Indicator 7 3_7 for step 7
8. Activation of the fuel consumption, and fuel tank gauges as well as speedometer and tachometer- needles in the third quarteer of the dial. Oil pressure gauge stays in the second quarter. Indicator 8 3_7 for step 8
9. Activation of the fuel tank gauge as well as speedometer and tachometer, needle in the fourth quarter of the dial, oil pressure remains in the second qurter, fuel consumption remains in the third quarter. Indicator 9 3_7 for step 9

[kayooh]

Myarmar,
Thanks again for a most informative reply.
Where do you glean all these pearls of Mercedes wisdom?
If it is a manual, please tell me what it is called and where to get it.

Also,
If this new procedure is initiated by turning the clock knob CLOCKWISE! what was the procedure which I initiated when I turned it COUNTER clockwise?!

Thanks again and I truly appreciate your constant help.

[myarmar]

Originally posted by kayooh
Myarmar,
Thanks again for a most informative reply.
Where do you glean all these pearls of Mercedes wisdom?
If it is a manual, please tell me what it is called and where to get it.

You can subscribe to Alldata for $25/year http://www.alldatadiy.com/
They have this information there. I also was able to pick up some factory manuals on Ebay, but that was expensive.

Also,
If this new procedure is initiated by turning the clock knob CLOCKWISE! what was the procedure which I initiated when I turned it COUNTER clockwise?!

I don't know. I checked it out in my car and it works the way you described.

Thanks again and I truly appreciate your constant help.

You're welcome

[kayooh]

Myarmar,
I performed the test as you have outlined and all the gauges behave as you have described. The resistance of the outside temp gauge always reads 59 Ohms.
So I am assuming there is nothing wrong with the gauges, so it is either the oil pressure sender or the power supply to it.
Then it dawned on me that I may have been missing with a sender other than that of the oil pressure!!
Please tell me where would the oil pressure sender be on a V12 engine?

The one I have been looking at is immediately behind the oil filter in the direction of the driver.

Thank you.

[myarmar]

What was the oil pressure reading in test step 3?
Here is a picture. Pressure sensor is item 25

[kayooh]

Thanks again, you always come through.

That is what I had thought to be the oil pressure sender.
The reading in step 3 was 0-0!!

Thank you very much.

[myarmar]

With engine running it should be 3_0 or so. I think you either have bad sensor or bad wiring.