"Check Gages" light, oil pressure at 0

[dhanger]

I didn't even know that light existed, never paid close attention to all the lights that come on just before starting and it's never come on in all these 22 years. So I did what the light said, I looked at all my gages and saw the oil pressure was reading 0. So, what is this telling me? Is there a problem with the oil gage itself or is it more likely that the pressure is actually 0? Obviously I don't want to take any chances with this one. I know the gauge on this car is phony, no better than an idiot light so a pressure reading only tells me whether there is any pressure or not. Check engine light is not on so I haven't checked for any DTC's. Oil level is full.

Three options I can think of: gauge is bad, sender is bad, oil pickup tube has given out (I know there's an issue with the pickup tube seal on this engine going bad). I can check for a signal at the sender, just have to wait until the morning when things have cooled off. Does a good bidirectional scanner show the actual oil pressure or is it just going to be whatever the sender/gauge is going by? I bought an Xtool A30M recently but don't know it well enough yet.

 

[TJBaker57]

Does a good bidirectional scanner show the actual oil pressure or is it just going to be whatever the sender/gauge is going by?

No scantool can read oil pressure for the 6 cylinder 4.2 engine as there is no sensor that can read that.

Query: What was the engine temperature when this warning came and what was the engine rpm?

 

[dhanger]

I only noticed the light when I pulled in after a short half hour trip. All other gages were normal so temp was right about the 210 location, and this was at idle.

 

[movietvet]

No scantool can read oil pressure for the 6 cylinder 4.2 engine as there is no sensor that can read that.

Query: What was the engine temperature when this warning came and what was the engine rpm?

I use this voltage scale to read my oil pressure, on my 2005 Tahoe Z71 5.3, thru my scanner. I match it up with my oil pressure gauge and it is very accurate. @TJBaker57, are you saying this scale would not work on the 4.2? I would be interested in knowing.
@dhanger, are you hearing any odd noises? Is the oil level full? If is the oil pickup o-ring, that would be very rare to go from good pressure to bad pressure, in one engine cycle. The o-ring is known to cause low oil pressure, that can also fluctuate depending on incline.
Could be a failed sensor. I would attach a manual gauge and see. I was surprised to see that you had not checked oil level. Maybe a failed oil filter?

 

[dhanger]

I did check oil level, you just missed it. Oil filter--your question about that just jogged my memory (it's getting shorter all the time LOL). I did an oil change about 500 miles ago with Valvoline R&P for the first time, and I had read about some people having the filter get clogged up pretty quickly and needed to be changed long before the next oil change. In fact I just ordered a new filter and was just about getting ready to do a preemptive change on it. I don't know why that didn't occur to me, guess I went into panic mode. I'll do that first thing tomorrow morning and see what that does.

Edit:If the filter is indeed clogged and it goes into bypass, does that bypass the sending unit?

 

[dhanger]

Oh yeah, to answer your question about noise, there was no engine noise so that's a bit reassuring.

 

[movietvet]

I see where the oil level check is. Sorry.

I use Valvoline R&P myself but have never heard of the filter getting clogged within 500 miles. But, is worth a shot. I would feel better with the manual gauge and see what it says.

 

[dhanger]

I would feel better with the manual gauge and see what it says.

I would too but I don't have one. I do have a fuel pressure tester but not sure if that would work or just foul up the tester. Does anyone happen to know what type of thread the sending unit uses? I'm guessing NPT 1/8 or 1/4 maybe?

 

[Mooseman]

First of all, the 4.2 oil pressure gauge is FAKE:

Trailblazer oil pressure gauge doesn't tell you the oil pressure (4.2L engines)

99% of the time, the oil pressure SWITCH has failed. Because you got both the 0 fake oil pressure AND the check gauges light (meaning that the stepper motor for the gauge is fine), the switch is not working. Replace the oil pressure switch (located just above the oil filter) and recheck.

No scantool can read oil pressure for the 6 cylinder 4.2 engine as there is no sensor that can read that.

use this voltage scale to read my oil pressure, on my 2005 Tahoe Z71 5.3, thru my scanner. I match it up with my oil pressure gauge and it is very accurate. @TJBaker57, are you saying this scale would not work on the 4.2? I would be interested in knowing.

You're both wrong, sort of. The Tech 2 will show oil pressure however it's the FAKE fabricated pressure by the PCM.

 

[movietvet]

First of all, the 4.2 oil pressure gauge is FAKE:

Trailblazer oil pressure gauge doesn't tell you the oil pressure (4.2L engines)

99% of the time, the oil pressure SWITCH has failed. Because you got both the 0 fake oil pressure AND the check gauges light (meaning that the stepper motor for the gauge is fine), the switch is not working. Replace the oil pressure switch (located just above the oil filter) and recheck.



You're both wrong, sort of. The Tech 2 will show oil pressure however it's the FAKE fabricated pressure by the PCM.

I get it, I do. The mechanical gauge shows actual pressure but the voltage readings are live data that can change depending on load and engine speed. I know it is not as accurate as the mechanical gauge but it should be as accurate as the oil pressure "sensor" readings at the dash. maybe even more accurate. Right? I am not using a Tech 2, I am using a Foxwell NT710 GM specific scanner and an Autel 808S multi manufacturer scanner.

 

[TJBaker57]

You're both wrong, sort of. The Tech 2 will show oil pressur

Well allow me to rephrase...

MY Tech 2 on MY 2002 4.2 does not display "oil pressure".





I have tested a few oil pressure switches from the 4.2. They are a basic ON/OFF (open/closed) device. They are normally closed and they open at approximately 4 psi. This is all that any typical scantool can get from the PCM of a 4.2.

There is no variable voltage to or from this switch. It is a YES/NO device.

 

[TJBaker57]

Does anyone happen to know what type of thread the sending unit uses?

The oil pressure SWITCH threads are M16 x 2