Sue };-) I have a whole new respect for you .
From:
[email protected] (Palindr☻me)
Alistair Ross wrote:
New to the group, so apologies if this question has been asked before.
My car is fitted with a sensor that tells the ECU that manages the auto
gearbox what RPM's the engine is running at. The error code on the car
points to the sensor not sending the RPM's to the ECU
Before I fork out £60 for another sensor is there a way of using
digital multimeter to test it?
The unit is a plastic moulding with two wires, and has quite a strong
magnetic field.
Anyone know of a layman's guide to testing gadgets and gizmos found on
modern cars on the web??
My level of expertise?....Novice!
All help appreciated.......ttfn........Alistair
Firstly, it may not be the sensor but the electronics pack to which it
is connected. However:
The simplest of these just has a magnet with a coil of wire wrapped
around it and works by producing a small electrical output as the teeth
of a gear wheel rotate into and out for the magnetic field produced by
the magnet. As this couldn't be a lot simpler, they seldom go wrong -
but their position relative to the gear wheel is very critical. It may
be that it doesn't require replacement but simply needs to be set
correctly in relation to the gearwheel teeth. It may have vibrated out
of adjustment. The vehicle maintenance manual will have the setting up
instructions.
One of these sensors can be tested for basic functionality by simply by
putting it across the terminals of an analogue microammeter and moving
the sensor towards and away from a steel object - the needle of the
meter should swing as you do so. It is less easy to do with a digital
meter but you may be able to see that the meter is reading /something/
as you move the sensor.
You may have a different type of sensor though - some use the two wires
to power an active electronic, self-compensating, sensor from a constant
current supply. The sensor gives an output by varying the impedance of
the device as seen by the power supply and hence changes the supply
output voltage. These units can only be tested whilst connected to a
suitable supply. I can't think of any harm you can do to one by simply
connecting it across a microammeter, though - to see what it does. These
more complicated sensors are used because their exact positioning is not
so critical and their output is amplified and low impedance and thus far
less effected by ambient electrical noise - of which a lot exists in an
engine compartment. Because they produce a much larger output, the
electronics pack to which they connect can be made correspondingly
simpler and less likely to go wrong.
Testing these needs special equipment - although a 'scope
will do the job nicely.
In my experience, these seldom go wrong but much more frequently are
knocked or vibrate out of position.
