I’m looking for technical help or recommendations on: __ABS sensor
I’ve been having problems with my aftermarket cruise control. It used to work fine but now surges as it attempts to find the speed I’ve set it to. I contacted the manufacturer and they said their units never fail (really?) so it must be a sensor issue. My garage has checked all four sensors and can’t find anything wrong with them. So, I decided to invest in a digital oscilloscope to see if I could identify anything wrong with the sensors.
I’ve included photographs below of the readings I got. I noticed that the rear sensors produced an almost square waveform, which is what I expected, while the waveforms from the front sensors were slightly spiked.
But, the “spiky” ones are also much lower voltage level. This suggests either a bad connection or something putting extra load on the signal lines by the point where you read them, or both. Check the plugs and sockets are clean, dry and not tarnished.
Quite often a good squirt of Servisol and some exercise (plug/unplug/plug/unplug a few times etc) can restore a good signal circuit.
It will also help remove WD40 applied in error. Original WD40 is an excellent electrical insulator.
My cruise control unit picks up the signal from one of the white wires behind the gauges. When you say ‘stable reading from the speedo’, do you mean, is the needle steady when driving?
Only ever come across that in terms of compressors, what does it mean for cruise control? Is it whether the system maintains a constant throttle or will let the speed drop and speed up again? I find this thread very interesting.
As far as I know, those sensor readings should be ok, but I’m just an enthusiastic amateur. The sensors are read as a 0 or a 1, as all they’re really doing is counting, so specific voltage values don’t matter, in as much as the signal needs to be strong enough, as long as they are sending a varying signal then the system can read 0 or 1 and count wheel speed as a result.
One would think that if you had sensor issues, you would get ABS/traction control light, or other such error notification in the vehicle’s ABS computer. Also, as CBRDeano said, if you’re reading from the same source as the clocks and the clocks are fine, you should be fine. I’m not entirely sure that the wheel speed sensors actually have a profound effect on the signal that is sent to the speedo on these particular cars, but I would love for someone to confirm or deny that for me.
If it’s not simply your settings on the CC unit, you know what causes throttle surges? Vacuum leaks. Make sure you’re only drawing in metered air!
I too am from a compressed air background.
The adjustment is to change the behaviour of the cruise control reaction.
In compressor terms - moving it from an on line/off line operation to controlled modulation.
The universal cruise control is not aware of how reactive each car is to throttle input so an ultralight caterham would react much faster than a large suv to the same throttle input.
( Much like having a large compressor on a system with low storage volume )
Tweeking the cruise control to each vehicle reduces constant throttle surge
If you install the TORQUE app and a bluetooth OBD dongle - you can have throttle % as one of the readings.
This would tell you if the cruise control is changing the throttle setting OR if the car is changing speed for the same throttle setting.
You can also put SPEED up on torque to see what the car thinks it is doing.
