Joe wrote:
On Wed, 11 Sep 2019 13:30:13 +0100
"Dave Plowman (News)" wrote:

In article ,
tim... wrote:
Well some of the exhaust sensors can fail and the engine will run,
just at high emissions for example.

some sensors can fail and the engine will still run normally

Which ones would those be?


Not the crankshaft position sensor.


Possibly the worst one to go :-)

But the emissions sensors generally provide feedback. If one fails, the
engine light will come on and the engine management system will use the
last available settings from when the sensor was working. In the long
term, the engine will drift out of emissions spec. but it will go on
running reasonably well for a while.

Early engine management systems used a default set of values after
sensor failure, which would generally get you home but was quite poor.
It's a bit more sophisticated today.

But to drift back to the topic, my current car has tyre pressure
sensors, which are literally more trouble than they are worth, as they
are worthless. They are not particularly accurate, and apparently put
more wear and tear on valve bodies than formerly. I've had to replace
two valves, at a cost of about thirty pounds, which have torn around the
seating. Again, light on, MOT fail, regardless of the actual tyre
pressures, which of course are a potential failure point in their own
right.


Did you have an actual fail for a tyre pressure warning? That seems a
bit harsh, unless they are are obviously visually low.