Dummy gauges

[Razor]

Had a local person I was helping out with a Trailblazer. The problem is the oil pressure gauge reads from 40 drops to zero then goes back to 40. So we start thinking sending unit, gauge , etc..

Well get this, the sending unit on this 2002+ Trailblazers is just a switch that does not vary its signal. Either you have oil or you dont. If you dont have oil pressure it shuts down the motor.

The computer basically fools the owner of the vehicle by varying signal to the stepper motor on the instrument cluster making a "feels good" scenario based on RPM. So you see the gauge move but it has nothing to do with oil pressure.

Wonder how many car MFG's do this

You go buy a vehicle.. see it has oil pressure.. say to yourself.. all looks good.. NOT

Wonder if Battery volts, temp, or any other work this way?

My Mustang 5.0 factory dash has an oil pressure gauge. The screen says Low-High. The needle only goes half way becuase there is a peg in the movement that does not allow it to go any higher. So at 100 PSI.. it reads half way. Another one of those fool the owner.

 

[novaderrik]

it's easy to tell a pressure switch from a true pressure sending unit- a switch is small, and a sending unit is larger.
i looked up a 2003 Trailblazer on the NAPA website, and that does indeed look like a switch.

 

[Razor]

Especially when it only has two wires coming from it. Sending units have 3.

Why the need to fool people? What could the cost have been to have used a sending unit and an accurate gauge? Guess if you sell 100000 vehicles.. even a 1.00 is $100,000. They use stepper motors to run the gauges..

Just cant believe gauges anymore unless you go digging for the truth.

Yesterday I unplugged the switch and started the truck.. oil pressure gauge went to 40 PSI on the dash

 

[Quiky One]

The GM factory gauges are notorius for this. I run an OBII digital gauge for accurate info.

For instance, the coolant gauge reads 170 degrees when it is 120, then the coolant gauge reads 210 from 180-230. After that is starts to move...this way no one complains about the car overheating.

My oil pressure gauge is accurate though.

Jason

 

[novaderrik]

the gauges are just there to make the car feel more "sporty". notice how a lot of late model temperature gauges only have vague 'zones' on them- "cold" "normal" "hot"- instead of actual numbers? that's because most people would freak out if they saw their temp gauge running at 230 degrees all the time.

and a sending unit for a gauge doesn't need to have 3 wires- they can have a single wire if it is just a variable resister that runs the gauge varying the resistance on the ground path for the gauge.

 

[Top Speed]

Razor, my wife's 2008 Mazda MX-5 Miata does the same thing.

 

[injdinjn]

the oil pressure sender on my 85 GP is about 1.5in dia and about 2in tall with one wire.

 

[TurboDave]

Almost all the manufacturers do their gauges that way (switch type sending unit)

 

[jasjamz]

My 2001 Olds Aurora 4.0(V-8)
has the digital driver information center and reads oil pressure. It is true reading and has only been replaced once. I guess it's the make of the car, and the gauge type.