Oil Pressure Gauge: 40 PSI engine off, 80 PSI, engine on.

TGFB87

Original poster
Member
Dec 27, 2011
14
Hey all,
This one just started happening....

03 TB with a 5.3,

Driving down the road and noticed that my oil pressure was very high. Gauge was still slightly moving with engine RPM.

Key off - zero, like it should.
Key on, engine off- shows around 40.
Key on, engine on- shows around 70-80.

Engine is new, got about 650 miles on it. Oil pressure has displayed fine up to this point.

Any way to determine if it is the sending unit or the gauge cluster or something in between?

Thanks in advance.
 

djthumper

Administrator
Nov 20, 2011
14,955
North Las Vegas
I am thinking more in the line of the stepper motor. I don't know if disconnecting the battery again will do much for that. you can take the dash apart and check the voltage to the gauges.
 

christo829

Member
Dec 7, 2011
507
Fairfax, Virginia
If it read 40 with the key off, I'd say stepper motor. With the circuit energized but the engine not running, if it jumps
from zero to a reading, it's most likely the sender. The resistor in the sending unit has most likely broken down.
The 5.3 has a real sender, not the switch and fake reading the 4.2 uses.

If you can get a meter on the sender, you can get some resistance readings off of it with the key off and key on but
not started (I'm not going to recommend crawling about the engine while it's running). Maybe someone here has their
manuals handy (I don't) and can chime in with the "normal" resistance readings from the sender. I'll see if I can look
them up in the morning if no-one chimes in before then.

Good Luck!

Chris
 

TGFB87

Original poster
Member
Dec 27, 2011
14
As a follow up, it was the sending unit. All is working well now.

After a while, the reading just got very erratic. Had it changed out this evening. It is not in a great spot, thats for sure. Friend had to disconnect the fuel lines to get to them without taking off the manifold.
 

racsan

Member
Feb 5, 2012
15
a co-worker who has a trailblazer told me of a similar problem hers has had lately. oil pressure reads 80 while driving, says speedometer is reading wrong too, when going through town it shows 60 when she's really running about 25-35. not sure if any other of the guages are affected.
 

christo829

Member
Dec 7, 2011
507
Fairfax, Virginia
racsan said:
a co-worker who has a trailblazer told me of a similar problem hers has had lately. oil pressure reads 80 while driving, says speedometer is reading wrong too, when going through town it shows 60 when she's really running about 25-35. not sure if any other of the guages are affected.

Now find out what they read when the truck is turned off. If they don't return to zero, it's the stepper motors.

Odds of multiple sensor failures leading to multiple gauge "misreads" are statistically poor, but I can't say impossible.

A poor ground connection usually causes more erratic behavior in multiple systems.

My bet is they don't return to zero with the truck off.

Cheers-

Chris
 

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