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Oil pressure gauge abnormality

A

Andrew04MN

Full Member
Joined
Oct 24, 2018
Messages
9
Location
Minnesota
:help:

I've got quite the interesting predicament with my 2004 Avalanche (5.3l v8, 216k miles). So about two years ago on one of our legendarily cold Minnesota days I started my Avalanche after work only to have my oil pressure go directly to 80psi (pegged/maxed) as soon as the key got to "Accesories" (not even on "Start") and proceded to stay at 80 after I started it and the whole way home. I figured the sensor kicked the bucket, but since I check my oil regularly and the motor ran smooth I didn't bother changing it until the next Spring.

I changed it, but the new one only lasted like a week before doing the same thing. Around the same time my dad got a new motor in his truck (Silverado with 330k miles) and I took his old working sensor and put it in my truck, but his didn't work at all in mine. After that I was at my wits end, thinking the screen I've heard mention of in the sensor hole was plugged, and I gave up.

Just to clarify, as soon as my key turns to even accessory, not even turning the motor over, the gauge pegs to 80psi. Now, in the last month or so, the gauge has started to bounce down to 0, up to 60, back to 0, and then back to 80 randomly while the truck is running. This causes the cluster to emit an annoying "ding ding ding" sometimes quite frequently. I know the truck isn't low on oil or has low pressure because its still running smoothly and quietly when it does this.

Things I've tried:
Replaced Oil Pressure Sending Unit (2 times)
Checked oil, changed oil/filter, changed type of oil in motor
Cleaned contacts on sensor plug


If anybody has any ideas for how I can fix this it would be greatly appreciated as even my mechanic has no clue (other than rewiring the truck).
 
Search STEPPER MOTOR in problems systems section.
 
My mechanic said his computer shows thats the sensor is sending it that reading though, so we didn't think it was a bad stepper motor. I've had bad stepper motors in the past, like my fuel gauge, and thats always an issue of not returning to empty or 0 or getting stuck.

Anybody else have a theory?
 
I do think this weekend I'm going to unplug the sensor and see what that does. If it continues then I know its the stepper motor, which I doubt since its pegging to 80 and then being erratic after that. Another reason I doubt its the stepper motor is the fact that my DIC chimes "Low Oil Pressure" when it drops/fluctuates, which it wouldn't do with a bad stepper since the cluster determines that off the reading not the needle. If it stops then I'll know its the wire coming from the sensor to the gauge. I can rule out the sensor itself since I've replaced that 3 times now.
 
If it helps you any, if the sensor were bad it would show 0 PSI and your mechanic will see an open circuit. HTH
 
Do you know if the wiring from the sending unit to the gauge is replaceable? If not, think I'd be fine unplugging it since all it does now is cause an annoying beeping?
 
The wiring doesn't go from the sending unit to the gauge directly - it goes through the PCM.  Since the mechanic said the computer was reading the same as the gauge the wiring problem is between the PCM and the sending unit.  That section of wiring would be much easier to bypass than between the sending unit and gauge because you wouldn't have to mess with getting through the firewall and getting under/behind the dash.
 
Okay sounds good, I'll just have to do some tracing this weekend and see if I can find a melted or broken spot or if its just a short.
 
Well, its on a loom of like 30 other wires so I just gave up and unplugged the sensor. My 4wd switch is also having issues, the lights not coming on or letting me switch between 2hi, 4hi, 4lo and such while the DIC says "Service 4WD". I just had the encoder motor replaced to fix this issue, but I guess its a wiring problem.

Considering moving on from my poor old Avvy in light of these electrical gremlins.
 
Sounds like a bad stepper motor to me. An easy way to verify would be with the Torque app connected to a Bluetooth/ODB2 adapter.
 
AirJunky said:
Sounds like a bad stepper motor to me. An easy way to verify would be with the Torque app connected to a Bluetooth/ODB2 adapter.
Click to expand...

If it was a bad stepper it wouldn't be returning to zero on its own and my mechanic's computer wouldn't be registering it as an accurate reading. I have one bad stepper on the cluster so I'm familiar with the symptoms. I also disconnected the sensor and its happily sat at 0 ever since.

I'm pretty sure its a bad wire somewhere, but idk how to go about replacing it since its in a loom of like 30.
 
Screw in a manual oil pressure gauge and see what you are actually getting.
 
EXT4ME said:
Screw in a manual oil pressure gauge and see what you are actually getting.
Click to expand...

Where do I find one that screws in to that specific hole?

Honestly I'm 100% sure now that its a wire. If my oil pressure was legitimarely at 80 all the time then suddenly 0 driving down the highway I'd be buying a new motor lol.
 
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