Guess the problem....

Cat 140H. Dealer did a service about a year ago. Machine has been playing up ever since. Briefly puts on the alarm under moderate engine load and logs a sensor supply voltage code.
Any guesses?

to my inexperienced mind the atmospheric pressure of 103 doesn't sound right?

Negative oil pressure?? No pressure means zero pressure.

Odd set of figures, is that with the engine running or off?

I looked at the picture before I read it and sensor supply came to my mind as well.

-2 oil pressure does not bother me.

But why is engine speed and oil pressure 0 when there is so much boost pressure showing?

Boost sensor unplugged or damaged? Birken found the red flag

It appears there are 2 different boost pressure sensors misreading, one is turbo outlet and the other might be the intake manifold, somebody with more specific info will have to comment.

Cmark said:

Briefly puts on the alarm under moderate engine load and logs a sensor supply voltage code.

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It would be nice to know what the Code was............

Shimmy1 said:

Negative oil pressure?? No pressure means zero pressure.

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It's a calculation. EOP sensor reads absolute pressure. the ECM takes that reading and subtracts the atmos press reading, then displays the result. The -2 is nothing more than a slight difference in two sensors.

Birken Vogt said:

It appears there are 2 different boost pressure sensors misreading,

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There are two pressure sensors in the inlet manifold. One reads absolute pressure, the other reads boost pressure (absolute minus atmospheric).
Line 5 - 413 kPa.
Line 6 - 413 minus atmos pressure 103 from Line 2 = 310 kPa which is near enough to the displayed 308 kPa to make no difference.

But as Birken pointed out the engine is not running. See line 1 - 0 RPM.
So why does it allegedly have 310 kPa (approx 45psi) of boost pressure in the intake manifold.?
It wouldn't ever see that even at full power on a dyno.

Wiring fault in the turbo boost sensors or in the branch of the engine harness that connects to them.?
Harness rubbing against something and worn partially through.?
Dealer tech trapped/squashed/cut something electrical when performing the service.?

EDIT: Sorry there is only one pressure sensor on the inlet manifold (the other one is temperature). It works exactly the same as the oil pressure sensor, displaying an absolute pressure value. The boost pressure value is calculated by subtracting atmospheric pressure from the sensor reading.

Those dam mice!!

Vetech63 said:

Those dam mice!!

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But in this case I’m betting the mice had 2 legs not 4.....

I'll have my own guess the problem in the dozer section this evening.

All good observations. As expected, Nige is straight onto it with his treatise regarding the relationship between atmospheric pressure and absolute pressure.

So the story is, the guy doing the PM service stood on the manifold pressure sensor and broke it. He replaced it with one that fitted nicely but for reasons that still remain unclear, the wrong part number. This led to three field service calls and another two new sensors. The trouble was that the new sensors were ordered by using the part number from the "old" sensor and not looking it up in SIS. The next stage was going to be a new engine harness but the customer asked yours truly for a second opinion before forking out the cash.

The moral of the story is that computers aren't always going to tell you what's wrong with a fault code. Always look for sensors that are giving, as far as the ECM is concerned, a plausible reading, but an implausible reading IRL.

Cmark said:

Always look for sensors that are giving, as far as the ECM is concerned, a plausible reading, but an implausible reading IRL.

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And FFS before replacing it always check the Part Number of the sensor with the Parts Manual or in SIS before ordering another one................

Nice! Now I need you Cat gurus to answer mine in the dozer forum. I puttingbit there shortly.

That's better.........

Cmark said:

So the story is, the guy doing the PM service stood on the manifold pressure sensor and broke it.

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Been thinking. How in the creation of Christ did he manage to stand on that sensor.? You'd need the hood off and why would you do that for a service unless you were doing something else at the same time.? I still can't see the need to be stood that high up unless you were replacing a lamp in one of the lights on the cab roof.
There ought to be more to this story.......... I buy that it got broke, I don't buy the how.

2000 hr service. Hood off for a valve set.

Cmark said:

2000 hr service. Hood off for a valve set.

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OK, I get that. According to what I know he shouldn't have been on top of the engine without a safety harness. Was he trying to cross from one side of the machine to the other for some reason.?

I dunno. Expect the unexpected I suppose?

Fred Gassit said it best - "You fuggin' caaaaaahnt..........!!"