Oil pressure coming and going

[Mounce]

Alright, today the TB started acting up. I haven't driven it yet to validate anything but I figured I'd go ahead and throw it out here to go ahead and get other opinions.

It was driven about 10 miles then when put in park the oil pressure went to zero (I know the gauge is a fabricated number) and the check gauges light came on because of it. I left work and got to it about 30 minutes after the incident.

Oil full, no codes, nothing appeared to be leaking. Started it a few times and it acted fine so I left and it got driven home. Going down the driveway (decent decline) it repeated, no pressure and check gauges light.

Couple hours later it was driven about 4 miles, issue repeated again when put in Park. Drove about 4 miles back home and coming down the driveway it happened again but then cycled back and forth, pressure coming and going. I'm told it runs and sounds fine while this all is happening.



I'm thinking pressure switch and that's why I let it get driven a couple more times. Doubt oil pump because it shouldn't come and go like that, if it went I figured it would stay gone. Filter is suspect of course but it's ACDelco so surely not. About 1500-2000 miles since oil was changed. Around 125,000 miles on the clock and of course has the 4.2.

Any other ideas? I'm thinking go ahead and get a pressure switch and possibly change the oil filter. About to go drive it and see if it'll act up for me.

 

[littleblazer]

If the oil pressure is marginal it would do it as well. If it's dropping at idle and fine while cruising I'd try and test idle pressure. I would say it's probably just the switch though.

 

[Mounce]

Took about 30 minutes but I got it to replicate. Pressure goes down, give it gas and it comes back but drops right back off as soon as idle. No noise or anything like it actually has no pressure. Hopped out and opened the hood and all sounded good. Looked down around the oil filter and can just barely see the sensor plug, noticed it was kinda wet when first looking at it before going on the drive. Also noticed it was wet below it on the frame and such. Hopped back in it and revved it up around 2k and held it for a little while. Got back out real quick and looked again and the oil looked real fresh. Then I saw it drip. Sensor is dripping oil. So, 95% sure that it's the sensor, since that's a common thing. Oil coming through the sensor, that is.

 

[Mounce]

ACDelco replacement ordered through Amazon prime. Can't believe the cost of that little sucker. Advance wants $50 and amazon had it for $37.

D1843A is the ACDelco part number in case someone searches and finds this thread in the future.

 

[littleblazer]

Think that's more then I paid at autozone for an actual sending unit for the escalade.

 

[Sparky]

Yeah switch sounds like a good place to start given the symptoms.

 

[Mike534x]

I had the exact same issue with my Envoy when we still had it. Once it was warmed up and driven for a bit, it would drop to 0 and the check gauges light would come on. The year prior we changed the pressure sensor because it failed, and used a BWD one from O'Reilly, a month or too later it did the same thing. Bought a Delco one from Amazon, installed it and sure enough it happened again, tried another Delco and the same thing.

The issue itself was sporadic, sometimes we could replicate it and sometimes we couldn't. It mostly did it if the steering wheel was turned a certain way. Tried different oils (changed from 5w-30 to 10w-30), 3 sensors, and a new Throttle body. It was in the dealer at the time for the blend door actuator failing, before taking it apart we had them test the oil pressure and it was showing no drops or anything when it was left running. No knocks (besides the spark knock on #6 since the plug worked its way loose), no metal shavings and a clean test result from Blackstone labs.

We contributed it to either a short somewhere in the wiring connector leading to the sensor or just getting unlucky and kept getting bad sensors. It kept doing it for almost 2 years before trading it in for my Avalanche.

 

[Moore]

Mine did exactly the same thing in July. The shop tested it out and put in a new sensor or oil sending unit. Has been fine since. I may have been lucky.

 

[Mounce]

I've seen that the connector can go bad from the oil intrusion as well when the sensor starts passing oil through. So, you fix the real issue but the symptoms persist. I'm hoping mine will be fine, just gonna spray it out with some brake clean or something to get the oil out.

If it comes down to it, connector + harness is readily available though. PN: S-955 on amazon.

 

[mrrsm]

The symptom @Mike534x describes is something rare that might be traced back to the point where the weight of the Dash Panel Harness pulls downward on the place where it plugs into the Dash Panel Circuit Board. What can happen is that some of the soldered contacts that are fairly thin can vibrate enough to cause the Cable and Plug to loosen the Pin Matrix Board attachments to the Dash Panel Circuit Board's soldered contacts at anything from individual pins to entire rows of pins... hence the sketchy electrical behavior when the Steering Wheel was being turned... making a contact when the local motion allows the wire harness to contact the pins and force the pins against the circuit board itself.

The solution here is fairly straightforward and is very similar to the procedures used to do the R&R of the Lights and Gauges, After disassembly... the DPCB is removed exposing the individual Pin Connecting Points. After getting heated up individually... and wicked clean with Copper Wire Braid and then Fresh Flux and Solder are applied in tiny amounts. Then after examining both sides of the circuit board for all of these connection points demonstrating solid connections... upon re-assembling the Dash Panel Unit and plugging in the Harness... all of the Gauges and Lights should function properly. The Dash Panel (Motherboard) is fairly Solid State and generally only has problems at the points where parts attached with Soldered In connections are prone to these rare failures. This video will demonstrate precisely how all of this should be done:

This is the Pin-out Diagram for a Typical GM Silverado 24 Wire Dash Panel Connector. Please Note the Position for the Oil Pressure Sending Unit:

This Video demonstrates the Soldering Repair on a Dead Cluster that Worked:

This video shows how to repair the Harness Connection Side as well:

 

[AtlWrk]

Good information but our oil pressure switch (on the 4.2L, and actual sensor for the 5.3L folks) goes to the PCM, not directly to the cluster.
The PCM then sends (faked) data over the databus to the cluster to tell it where to position the gauge. Same applies to coolant temp, fuel level and battery voltage.

Side note: the speedometer and tachometer are fed on separate dedicated lines between the PCM and cluster due to the need for accuracy and refresh rate that would overwhelm the databus.

 

[mrrsm]

Absolutely... and Thanks for rendering such an Elegant Explanation of how it all works. I only specify this to Mike's Case because other than a Cut Wire between the Oil Pressure Sensor and the PCM (Which may also have been a culprit here)...that Last Arbiter for viewing the output of any of these various circuits would be what the Driver can see on the Dash Panel... and so it is possible to have both conditions misbehaving simultaneously.

Its quite the shame really... because perhaps right along with some other repeating mechanical difficulties... he was obviously concerned enough to wind up getting a replacement vehicle. When our Oil Pressure registry disappears... nothing could be more frightening if that is really what is happening inside of these engines. Thanks Again @AtlWrk !

It would be nice if they made an Automotive Application of this Wireless OPG... but using a Bluetooth-to-Analog Tech in a small and rugged design ...and skip all of this "Digital Micky Mouse" in between what used to be something so very simple,direct and reliable:

http://www.us.stauff.com/index.php?id=3632

 

[AtlWrk]

Funny you mention that. I saw this a few weeks ago: http://www.mouser.com/ProductDetail/Measurement-Specialties/U5600-000005-100PA

Granted I'm not about to spend $200+ for the novelty but it's still pretty neat.

Edit: better link:
http://www.mouser.com/new/measurement-specialties/measurement-specialties-u5600/

 

[Mike534x]

Absolutely... and Thanks for rendering such an Elegant Explanation of how it all works. I only specify this to Mike's Case because other than a Cut Wire between the Oil Pressure Sensor and the PCM (Which may also have been a culprit here)...that Last Arbiter for viewing the output of any of these various circuits would be what the Driver can see on the Dash Panel... and so it is possible to have both conditions misbehaving simultaneously.

Its quite the shame really... because perhaps right along with some other repeating mechanical difficulties... he was obviously concerned enough to wind up getting a replacement vehicle. When our Oil Pressure registry disappears... nothing could be more frightening if that is really what is happening inside of these engines. Thanks Again @AtlWrk !

It would be nice if they made an Automotive Application of this Wireless OPG... but using a Bluetooth-to-Analog Tech in a small and rugged design ...and skip all of this "Digital Micky Mouse" in between what used to be something so very simple,direct and reliable:

http://www.us.stauff.com/index.php?id=3632

I appreciate the thought on the matter MRRSM, I wish I did hold onto it because I still think back once in a while on what of caused the check gauges warning to sporadically occur, other then that there was really nothing else wrong with it. I was concerned at first, but after seeing it had good oil pressure and nothing abnormal showing up in the oil sample I just learned to live with it. If I didn't come across the Avalanche browsing online, marked lower then the Dealers listed price, I would of kept the Envoy.

 

[Mounce]

Oil pressure switch replaced and all is good so far.