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01-22-2012, 01:01 AM #1
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- Dec 2011
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Oil Pressure Sensor replacement 2004 Silverado 4.8L 2WD
Oil Pressure Sensor replacement
2004 Silverado with 4.8L V8 engine, 2WD, 152,000 miles.
Symptoms and Diagnostics
The oil pressure gauge suddenly started reading 79 PSI whenever the engine was running, and read zero when the engine was not running. With the key ON, but the engine not running, it read zero. Previously, the gauge had read about 45 PSI when running, and would go up and down some with engine RPM, but in this new mode, it was always 79 or zero. I say 79 because it wasn’t quite pegged to the max of the gauge, but seemed to be showing a valid reading. This convinced me the Oil Pressure Sensor had gone bad, and I assumed that the gauge was working OK. Thinking back, I recalled that I had accidentally overfilled it during a routine oil change, and am wondering if it’s more than a coincidence that two weeks later this sensor fails.
Here’s the sensor, the object of interest. Actually this is the old part after I got it out.
Note the tab at one side of the connector. This lines up with a latch on the cable connector. Keep this in mind, because after the new sensor is screwed into place, the connector will probably be rotated to a different position than the old one was, so you’ll have to twist the wires as you reconnect them.
Remove the plastic engine cover
Overview of the position I had to get into in order to reach the sensor. Notice my right foot down next to the driver side of the engine. If your feet are bigger than size 9, you might have trouble with this one.
Area of interest, from my vantage point once I’m in position. Note the little white circle near the center, which is a capped off AC line or something….serves as a useful point of reference for the rest of the pictures.
You can’t see the sensor, but it’s in a vertical position, screwed into the top of the head. If you’re good with a dental mirror, you can find the top of it, with two wires coming out of the connector. If this photo is confusing, the mirror is oval shaped, and cracked across the center.
The connector has a latch on the side of it; you can feel your way around it. Once you unlatch it, pull the connector straight up off the sensor. Here’s what the sensor looks like in the mirror.
Reaching your hand/arm into this area would be impossible if you’re any bigger than me….5’9”, 170lb. Your arm gets pretty cut up in the process, thanks to those arbitrary sharp features GM puts on for fun.
By using the new sensor for reference I found I had to buy a deep 27mm socket. This worked fine, but after installing the new sensor, I found that the socket’s outside diameter was so large, it would wedge itself in place on the top of the engine and I couldn’t remove it once the sensor was screwed in. After removing and replacing the sensor 3 times, I finally wised up and ground down the last ½ inch of the socket to a smaller diameter, and it no longer got stuck in place. My socket was originally 1.410 inch diameter, and I ground it down so it tapered from 1.350 dia at the end, to 1.375 dia about ½ inch from the end….this was enough to keep it from getting stuck. Notice the red ring, which helps you find this in later photos.
Here’s the tool string I needed to use in order to reach in there: 27mm socket, which turned out to be ½ drive, so I used an adapter from the ½ square drive to a ¾ hex, then a ¾ hex socket, then a 3/8 universal joint, then an extension, then finally the ratchet handle.
Here’s the socket in place on the sensor, with the first adapter in it. This is tall enough so you can actually see the red ring, even though you can’t see the sensor.
Here’s the tool string in place.
Once you have the tool in place, it’s pretty simple to unscrew the old sensor, screw in the new sensor, plug the cable back in, and test. Simple, but not easy....no room for big fat hands, can't see what you're doing, getting all scraped up. Just don't drop anything or you'll never see it again, and it will eventually fall out on the road and break someone's windshield!
This solved the problem for me, the pressure reads in the high 40s, and fluctuates with engine RPM, so all is well. Good luck.
08-26-2012, 07:12 PM #2
- Join Date
- Nov 2010
- Ann Arbor, MI
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I just swapped my oil pressure sensor out on my 2003 Suburban 5.3 Flex 4WD and was going to post the procedure here but yours is well detailed and pretty much the same steps that I went through, although I did not have the interference issues you did with the 27 mm socket and used 1/2" drive socket wrench components.
My oil pressure was pegged at 80 psi when the key was in the ON posn without the engine running and also with the engine running but would return to zero when turned off. Now it is functioning properly.
I have approx 142K on my Suburban right now and my next fix is the right downstream O2 sensor. Hopefully that will take care of her for another 140K
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