How do electronic oil pressure gauges work (and why does smacking it fix it)?
10-16-2011, 02:32 AM
#1
ATGATT
Thread Starter
Join Date: Nov 2008
Location: Wangan
Posts: 10,477
Likes: 0
Received 0 Likes
on
0 Posts
How do electronic oil pressure gauges work (and why does smacking it fix it)?
My oil pressure gauge has started getting stuck at the top (the gauge is such that when driving it should normally be pegged at the max). It will work again momentarily if I hit it. I have noticed that when the ignition is on but the car is off it will read 0.5bar instead of 0bar, and no amount of smacking will fix that. It is hard to find used clusters in the condition mine is in, and a new pod is over $500, so I'm hoping there is a way this can be fixed. I didn't see anything obvious when I took it out.
10-16-2011, 05:28 AM
#2
Registered member
Join Date: Nov 2004
Posts: 6,252
Likes: 0
Received 0 Likes
on
0 Posts
Re: How do electronic oil pressure gauges work (and why does smacking it fix it)?
Sending Unit:
mostly their piezo electric strain gauges. A certain area of a piezo ceramic crystal is exposed to the oil. As the pressure increases, so does the voltage output.
Common issue with these is that due to mass production, they swage everything together. For this, the crush percentage on the o-ring seal wanders. Over time, oil will get passed this seal and ground out the electronics, causing for a max PSI reading.
Actual Gauge:
I don't know your specific setup; its on your mercedes I take it? Usually its a 0-5 signal that runs through a coil on the gauge itself. As this signal increases, so does the force on the coil, essentially moving the needle (this is me being hugely electronically naive). Sounds like you have a short ground somewhere. When you hit it, you're breaking the connection. If you pull the cluster off, look for broken solder joints or areas it could be making contact somewhere else.
mostly their piezo electric strain gauges. A certain area of a piezo ceramic crystal is exposed to the oil. As the pressure increases, so does the voltage output.
Common issue with these is that due to mass production, they swage everything together. For this, the crush percentage on the o-ring seal wanders. Over time, oil will get passed this seal and ground out the electronics, causing for a max PSI reading.
Actual Gauge:
I don't know your specific setup; its on your mercedes I take it? Usually its a 0-5 signal that runs through a coil on the gauge itself. As this signal increases, so does the force on the coil, essentially moving the needle (this is me being hugely electronically naive). Sounds like you have a short ground somewhere. When you hit it, you're breaking the connection. If you pull the cluster off, look for broken solder joints or areas it could be making contact somewhere else.
10-16-2011, 05:44 AM
#3
Racetracks
Join Date: Nov 2002
Location: How long is a piece of string?
Posts: 15,668
Likes: 0
Received 0 Likes
on
0 Posts
Re: How do electronic oil pressure gauges work (and why does smacking it fix it)?
That's actually not too far off.. 
The gauge has a driver circuit that takes the signal from the sender and conditions it to drive the gauge coil. There might be a fatigued solder joint on the driver board that's causing the coil to be overdriven. Driver circuits like that rely on feedback to keep the output at the correct level, so if part of the circuit doesn't work then it can easily drive the gauge to the max or to zero.
The gauge has a driver circuit that takes the signal from the sender and conditions it to drive the gauge coil. There might be a fatigued solder joint on the driver board that's causing the coil to be overdriven. Driver circuits like that rely on feedback to keep the output at the correct level, so if part of the circuit doesn't work then it can easily drive the gauge to the max or to zero.
10-16-2011, 05:58 AM
#4
formerly si_zc_civic
Join Date: Sep 2005
Location: va beach
Posts: 101
Likes: 0
Received 0 Likes
on
0 Posts
Re: How do electronic oil pressure gauges work (and why does smacking it fix it)?
if smacking it fixes it, that usually means there is a loose connection somewhere. as Fabrik8 said, solder joints are common failure points in consumer electronics. my advice is to take it apart and look for a loose connection or fractured solder joint, loose pins/unseated pins in a connector.
Thread
Thread Starter
Forum
Replies
Last Post