intermittent oil pressure light
 

my 2003 mcs is at south bay mini (L.A.) for this problem. it begins only when the engine has warmed a little, but isn't consistent in any other respect: sometimes the light goes on under a depressing throttle, sometimes it's on at idle.

according to the dealer, it's not the sensor (changed), it's not the oil pump (pressure output checked), and it's not the harness rubbing on the engine (inspected.)

have any of you had a similar problem with a cause different from what's been already checked?

thanks.

i know this is a stupid question, but sometimes it needs to be asked. Is there enough oil in the engine?

yes!

if you pull out the dipstick does the oil have a milky white deposit

as when water contaminates it ???

nope. the problem has persisted right through a dealer oil change....

Reinspect the harness.
 

I had all the above symptoms and only after the harness was replaced was everything fine again. The worn through spot was not visable with the original harness still in the car.

Jeff

part number?
 

thanks jeff. i've told them from the start about other online posts about harness rubbing, but they say it's ok. do you have a part number for the harness that was replaced on yours? who was the dealer that did your repair?

It was the engine harness
 

I have a Sept 2002 build early model 2003. Ralph Schomp in Denver was the dealer. They first checked oil pressure switch (12 61 1 500 893) and replaced anyway, the oil pressure and level was fine, finally did the harness and all's well for two years. The mechanic had seen a few of our vintage cars that had this problem where after the engine harness (12 51 7 533 103) warmed up it sags and then rubs I believe on the back side of the engine.

Depending on which wire's insulation wears through first and grounds out you get the oil light. to quote the Service Invoice "Replace engine wiring harness. Shorted out on wire harness to Oil Pressure Switch".

My oil light would usually come on going up hill or if tapping the brakes coasting into a red light or stop sign. Only then would the harness short.

Good luck,

Jeff

thanks again jeff

ha! mine is also a 2003 model year built in sept. 2002!