99 Suburban LT 5.7 V8 4x4 Oil Pressure Sensor Location

We have a 99 Suburban LT 5.7 V8 4x4 with 210K miles. My wife was driving the vehicle the other day and while at a stop light the oil pressure got very low approximately 20psi according to the gage. I need to find the oil pressure sensor location to check the true pressure using a pressure gage but I can’t seem to find it. From what I’ve read it should be by the oil filter or by the distributor cap or on the underside of the engine. It’s neither around the oil filter or the distributor (using a mirror looking everywhere) nor on the underside of the engine. What I have found is two sensors. A sensor I believe by #1 and #3 spark plug (driver’s side) screwed into the block and a sensor on the passenger side of the engine (screwed into the block) accessed from underneath the vehicle. The sensor on the driver’s side of the vehicle appears to be the best candidate however neither of the sensors looks like the replacement part when I view the picture of the sensor online.
Any suggestions?
Your help is appreciated.

I think you are just missing it. Its screwed into the top of the block, or into a fitting thats screwed into the block, drivers side of the distributor. It's not easy to get to, it's there.

The sensor in the drivers side head is for the coolant temp gauge and the one on the pass side block is most likely the knock sensor.

as mentioned should be vertical mounted on top of engine next to distributor. remove distributor cap and you'll see it.

If the oil pressure is normal with cold starting but after the engine temp gets to the normal range the oil pressure drops I would suspect the engine is worn. usually the use of cheap oil and filters and going too long between oil changes causes the crank bearings to wear. the increased gap causes a loss of pressure.

installing a pressure guage would confirm if its the engine or sender.

if the engine oil pressure is 20 psi this is good enough ..just use high quality oil and filters ..stay away from fram..use ac delco , purolator plus mobil 1 ,wix.... you should be using only 5-30wt or 10-30wt oil..10-40wt oil will damage the engine. change oil at 3-4000mi...with non synthetics.

"if the engine oil pressure is 20 psi this is good enough ..just use high quality oil and filters ..stay away from fram..use ac delco , purolator plus mobil 1 ,wix.... you should be using only 5-30wt or 10-30wt oil..10-40wt oil will damage the engine. change oil at 3-4000mi...with non synthetics"

j cat,

Why would 10W40 damage the engine???? What about 15W50 Mobil1 synthetic???

I agree 20 psi is not bad considering the miles, if it were mine I would be using a 10w30 high mileage oil in the vehicle.

You all were correct. That dang sensor was on the driver’s side just on the other side of the distributor, pretty tough to get access. Oh you’ll need an extra-long 1 1/16” deep socket to get it removed. I bought a socket especially made to remove the sensor.
Interestingly enough my wife had just had the oil changed and not sure what was used. Will be changing oil and filter as suggested. Based on the mileage thought I might change the oil pump. What you think would it be worth it?

Love this forum!

Thanks again!

Changing the oil pump would be a "major job" and in my opinion unwarranted. Too many other thing to consider related to low oil pressure.

I think there is a plug just above the oil filter that will allow you to hook up a manual gauge to check the dash gauge for accuracy.

[quote=777stickman;6953093]Changing the oil pump would be a "major job" and in my opinion unwarranted. Too many other thing to consider related to low oil pressure.

I agree. The oil pump is a pretty big job. Change the oil and filter and drive it.

"if the engine oil pressure is 20 psi this is good enough ..just use high quality oil and filters ..stay away from fram..use ac delco , purolator plus mobil 1 ,wix.... you should be using only 5-30wt or 10-30wt oil..10-40wt oil will damage the engine. change oil at 3-4000mi...with non synthetics"

j cat,

Why would 10W40 damage the engine???? What about 15W50 Mobil1 synthetic???

Gm states 10-40wt is not to be used. also I have seen and have received reports of engine wear with the use of 10-40wt.

on the use of 15-50wt I have no idea how that would work out. perhaps the MPG would drop. not a good oil for low temps.

Ok thanks guys. We'll change the oil and filter as noted above and drive.

Thanks again for everything!

Ok thought I’d provide an update in hopes to get some more insight as to what we should do.
We have changed the oil regularly over the life of the vehicle, but by having it done by someone else most of the time the quality that was used is defiantly in question. With that said we changed the oil and filter as noted above. Finally purchased an oil pressure gage and checked the oil pressure. On cold start the oil pressure went to 40 psi and as the engine warmed up the oil pressure began falling until it got to about 16 psi (where I turned the engine off). During acceleration the pressure would increase as one might expect. Engine sounds and runs great. We would really like to get another year maybe more out of this vehicle. What should we do now if anything?

Ok thought I’d provide an update in hopes to get some more insight as to what we should do.
We have changed the oil regularly over the life of the vehicle, but by having it done by someone else most of the time the quality that was used is defiantly in question. With that said we changed the oil and filter as noted above. Finally purchased an oil pressure gage and checked the oil pressure. On cold start the oil pressure went to 40 psi and as the engine warmed up the oil pressure began falling until it got to about 16 psi (where I turned the engine off). During acceleration the pressure would increase as one might expect. Engine sounds and runs great. We would really like to get another year maybe more out of this vehicle. What should we do now if anything?


the use of low quaility oil and filters and also going to long on the oil changes will cause these problems.

If you use the proper oil and filters and change 3-4,ooomi the oil this oil pressure should not get worse. usually the engine does use oil with the low pressures .

oil change shops also don't allow the proper time to drain all the oil out and also the engine must be hot to have the contaminations removed. never change oil on a cold engine.

anything above 10 psi you should be good.

if the engine was not worn the cold start pressure should be 70psi. as the engine warms the pressure should stay between 40-50psi.

good luck.

Oil pressure specs for your truck are: Eng at normal operating temp, MINIMUN pressures of 6psi at 1000rpm, 18psi at 2000rpm and 24psi at 4000rpm.
With what you are reading, I would drive it.

Well then we'll just drive it! We'll let everyone know how long she go's.

Thanks again to everyone, this forum is GREAT!