I'm truly at a loss now, I have a 03 MCS, 52K miles. Bought it in Dec. and on day 1 got a flickering oil pressure light. Scanned board and changed oil along with replacing oil pressure sender to the idiot light. All good for 2500 miles then light came back on, talked to George at Madness and suggested dropping pan. I had a seep from pan along with CPS leak so what the hell why not. Nothing noted all looked good and replaced pan gasket along with CPS o'ring and completed oil change with OEM filter. checked inside filter housing all parts are there and appear to be in correct places. I decided to add a oil pressure gauge while I was doing some other mods (More on them later) and followed "Bill Web's" procedure utilizing- Cravenspeed adapter and SCX gauge and AMS remote oil line to isolate sender from engine vibes. Started her up and checked for leaks all good with oil pressure and no light. Then went for a 5 minute drive to check out new LCA bushings and suspension upgrades (IE fixed camber plates, Koni Yellows and Madness springs- Wow what a difference). Oil pressure was around 60psi at cruise/3000rpm and 20 at idle, pull back in the garage to recheck everything and F'ning idiot light is back on and with pressure at 20 psi. I'm thinking the idiot light sender has failed again but it is less than 6 months old.


Any ideas or suggestions? Sorry for the novel

 

A random thought- the body on that pressure switch should be the ground. Did you use Teflon tape or some such when you installed it? (I think it's a pipe thread fitting). Too much tape can mess with the ground and create intermittent problems.

 

I did use Teflon tape and checked the ground through to the pressure gauge sender but didn't check the light sender. I'll check tonight, I'm open to anything now. Does anyone know how you would check the wiring for a possible short, I've read that somewhere as well...

 

If you have a Bentley manual, the oil pressure switch wiring diagram is page ELE-220 in mine.

Here is the text version. The oil pressure switch is called component B6231.

The housing is ground.

The signal wire is blue. It remains blue until it gets to the control module for the instrument cluster

It goes to pin 3 of connector X6011, which then goes to pin 37 of connector X15, which then goes to pin 19 of connector X111777 on the control module of the instrument cluster. Pin 16 of connector X11177 is the output from the control module to the lamp.

But I can't find where it says where the connectors are. ARgh.

Section 119 helps a little. It says the switch is normally open, and grounds the signal wire out when pressure is low.
It says you can test the wiring and control module this way:
1) remove the sensor wire from the oil pressure switch. Light should be out and stay out.
2) connect sensor wire to a good ground in the engine compartment (clean metal, etc). The light should illuminate.

 

Thanks, that's perfect and will really help. I'll check the ground and wiring tonight.

 

You can take a look at our DIY Tech Articles as well to see if you can find anything helpful in there. If not, you can always give us a call and speak with a specialist. Good luck!

-Luccia