Sigma oil pressure gauge not working - resolved

[RetroRob]

Hello,

I have a (new build by other person) 2012 Sigma engined roadsport I am debugging.

The oil pressure gauge is not moving (very slight movement at ignition switch on).

Tried unplugging/replugging the round rubber connector that attaches the sensor fly lead into the car wiring.

Tried pulling and refitting the plug into the back of the gauge.

Is there a reading I can check with a meter?

Thanks Rob

[Jonathan Kay]

Yes, you can check the resistance across the sender and how it varies with engine speed. Best done with the wire disconnected. If it's working you'll see the change in resistance. And someone here will probably know the nominal resistance range.

Before doing that have a good look at the wire and the contact at the sender.

...

You can test the gauge by disconnecting it and giving it a full 12V feed and an earth.

...

Please let me know if you'd like a copy of the wiring diagram

Jonathan

Edited: I'm out of date. See post #6 bellow. Sorry.

[RetroRob]

Jonathon, thank you.

Yes a wiring diagram would be most useful. I will pm you cheers Rob

[ChrisC]

Check the lead between the round rubber plug and the sensor.  There is a resistor and a diode soldered in the wire.  The joints can break very easily. 

[ChrisC]

For reference look at this post

https://www.caterhamlotus7.club/forum/techtalk/oil-pressure-360r

[Roger Ford]

IIRC correctly it's not a resistance, it's a voltage. There are three wires in, (ref, out+, earth) I think the ref contact takes a +5V input, and the output is between 0 and 5V. I've got a datasheet somewhere but can't find it at the moment.

Actually there are four wires - one of them is oil temp out but that's not used in the Caterham setup (and doesn't work properly on mine - don't know if Caterham found a stock of faulty sensors where the temp part didn't work).

 

[Jonathan Kay]

"IIRC correctly it's not a resistance, it's a voltage. There are three wires in, (ref, out+, earth) I think the ref contact takes a +5V input, and the output is between 0 and 5V. I've got a datasheet somewhere but can't find it at the moment."

Thanks for the correction. 

Previous discussions with Danfoss and other part numbers:

https://www.caterhamlotus7.club/forum/techtalk/sigma-danfoss-oil-pressure-sender-where-do-i-get-one
https://www.caterhamlotus7.club/forum/techtalk/sigma-oil-pressure-guagesensor

Jonathan

[RetroRob]

Thanks, much appreciated. I will check the above later and update.  Rob

[RetroRob]

The fault was with the short loom. Cut open and the resistor leg had corroded off.  And this on a car with 2 miles on the clock and 9 years in a carcoon.

So a rubber plug one end, an open U bend the other. Right next to a hot engine the perfect moisture trap.

Resistor was 220ohms. Cleaned up, resoldered, new resistor and heat shrink fitted but now sealed at both ends.

Pressure reading now on start up, just over 4 and rises when blipped.

Thank you for the advice and links above. Would never have guessed they had fitted those in that location.