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2002 chevy trailblazer_ls
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Discussion Starter #1 (Edited)
I have been reading threads for hours and I think I am more confused than ever! LOL I know there has been alot of posts about the oil pressure dropping to 0 when a car idles and I have read all the responses about the oil sending unit. I also read that cars with a light have an oil pressure switch and cars with a gauge have an oil pressure sending unit. My trailblazer which is a 2002 LS has a light and a gauge so Im not sure which one it is? Also, my car was not stalling or making noises when the pressure would drop, does that mean it is more likly to be the sending unit/switch? I checked my oil and it did not appear to be low....I read that you can disconnet the unit/switch and then start your car and if the gauge stays at a normal pressure then it is probably the unit/switch failing. I can't even find the unit/switch in my car IDK where to even look. I know everyone is saying its by the oil filter but I thought the oil filter was under the hood not under the car itself...I don't know much about cars which Im sure is obvious but any insight on this would be truly appreciated!
 

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2004 gmc
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26,181 Posts
If you want to do more work on your vehicle, I'd start by buying the Haynes manual, either on Ebay or the local parts store. Then you can locate the oil filter easily.

The truth is this: The I6 engine, which you have, has a switch near the oil filter. It sends an ON/OFF signal to the engine computer. If the pressure is low, the computer turns on the idiot light. The computer also makes up a number to display on the gauge. It's not a precise or truthful number, just something to look at and feel like GM gave you your money's worth.

Some members have a dirty throttle body or other problems that cause fluctuating idle that can stall out the engine if the RPMs get too low. When that happens, the oil pressure goes to zero as a RESULT of the low idle or stall-out and that's not an oil system problem.

Other folks have a failing oil pump or pressure switch, and then you can have a bad pressure indication without the idle RPM fluctuating. That might be what you have, and changing the oil pressure switch is definitely cheaper than getting at the internal oil pump.

Again, for more reading, better organized for new mechanic-wannabes, I recommend any one of a number of library books on beginning auto repair, plus the Haynes manual.
 

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2004 chevy trailblazer_lt
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[EDIT: Scooped by the Roadie... :) I can just never type fast enough!]

If you have a V8, you've got a real transducer/sending unit. The I6's have the switch.
The gauge for the I6 is just showing what the PCM wants you to believe. So gauge
vs light isn't the way to differentiate.

As far as the location, you have to get under the truck, take the plastic cover plate off
from under the oil pan, and look up by the front of the engine. The oil filter housing
is on the passenger's side towards the front of the access hole, and the switch/sender
is in the filter mount.

Often, members here will go to Compnine.com and use the diagrams there to find part
locations and numbers.

You could have a bad switch, bad wiring or possibly even a failing gauge. It didn't sound
like you were seeing your rpms dropping when the gauge went to zero. Does your dash
gauge go to zero when you shut the truck off? If not, it's the gauge itself and the stepper
motor that drives it that' at fault.

Not sure how deep you want to get with it. If you can get an analog gauge attached to
one of the other ports on the filter mount, you can see what the pressure really is, and if
it's really dropping to zero.

Good Luck!

Chris
 

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2002 chevy trailblazer_ltz
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Help!!!

I just had my timing cover (plate) seal replaced because it was leaking oil. The 'mechanic' tried to take the cover completely off but couldn't. It was 'stuck' on something inside. It only pulled ouit about an inch or so.
So he just inserted the seal and put some sealant around the cover rim and put it all back together.
Now after the truck runs a little bit, the oil pressure drops. Both the light comes on and the gauge drops and a message flashes that says turn of engine.
What is behind the cover that didn't allow him to pull it off? Could he have damaged my oil pump?
We did find that there was almost no oil when we first turned it back on. Once we added oil it seemed fine. But I drive for a little bit then in idle it drops again....
 
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