PSD dashboard light
04-20-2017, 06:35 PM
#1
5th Gear
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PSD dashboard light
Hi,
My s4 1991 was half parked on the pavement with its right wheels up and the left wheels on the road. The height is around 7 inches up from the road.
On two occasions now, I've started her up after an hour or so parked like this. as the dashboard lights have gone off, the PSD light remains on for around 30 seconds.
I was wondering if the light is indicating a low fluid warning caused by the lift up, is there even a fluid system involved in the PSD?
It doesn't stay on like this if its not lifted up by that type of parking.
Any ideas? is there anything I should do or be worried about?
Thanks,
Dom
My s4 1991 was half parked on the pavement with its right wheels up and the left wheels on the road. The height is around 7 inches up from the road.
On two occasions now, I've started her up after an hour or so parked like this. as the dashboard lights have gone off, the PSD light remains on for around 30 seconds.
I was wondering if the light is indicating a low fluid warning caused by the lift up, is there even a fluid system involved in the PSD?
It doesn't stay on like this if its not lifted up by that type of parking.
Any ideas? is there anything I should do or be worried about?
Thanks,
Dom
04-20-2017, 06:49 PM
#2
Drifting
The psd has a fluid tank in the rear driver side wheel well. You can check the fluid and also when was it flushed the last time. The psd uses brake fluid so should be changed every couple of years as it absorbs moisture.
04-20-2017, 10:17 PM
#3
Rennlist Member
The fact that it only occurs on an angle park, and goes out when back to level seems an indicator that it could be the lateral acceleration sensor under the LHS seat, triggering the PSD due to the angle. Doesn't sound like anything to worry about to me, but flushing the system is still a good idea no matter what.
Here's a very recent thread, which will give you a better understanding of the operation of the system, and give a few other things to double check and clean ... https://rennlist.com/forums/928-foru...m-for-psd.html
Here's a very recent thread, which will give you a better understanding of the operation of the system, and give a few other things to double check and clean ... https://rennlist.com/forums/928-foru...m-for-psd.html
04-21-2017, 06:48 AM
#5
Rennlist Member
Presumably we are tallking about the green PSD lamp.
The lateral acceleration sensor is quite a neat piece of kit but like everything else in the car that has not been replaced it is now 25 years old and most probably has not seen the light of day since since it was made.
As Dave astutely noted, when the car is at an inclination there will be a lateral component of "G" force albeit a very small one. The sensor measures that component very accurately and sends this feedback to the brains [the ABS computer] that reads this signal and the inputs from the wheel speed sensors to compute via a control algorithm an output signal to the PSD system that gives a controlled amount of lock up to stabilise the situation.
Until my recent thread I understood the green light to mean that some corrective signal was being sent to the diff but was advised that it only indicates that there is a condition that needs correcting [if I understood the advice correctly]. This surprised me somewhat but to be fair, no one attempted to correct that piece of advice so I tend to work on the principal that it is the highest level of info available and thus treat it with respect until such time as I have a better reason to believe otherwise.
Either way, it is the PSD system's way of giving the driver some feedback that a condition of some sort exists and hence a caution "to be wary". It would have been more useful if it could have a number advising the amount of lock up signal being applied but it is what it is and in theory should be a vast improvement over the earlier generation mechanical LSD units that are an on/off affair but not everyone thinks that way.
That your signal is going out - presumably after you move off, sugggests that the system is working correctly- whether it is being a bit over sensitive for some reason who knows but sady it is yet another of those "black boxes" that cost a shed load of $$$'s to fix when they go south as invariably they will do sooner or later. I removed my unit, took the lid off the unit - it looked spotless- blew it out with some air and boxed it up again. The sensor has what looks to be a spring arm and a Hall sensor detects lateral movement of said arm. FYI- If it does go south John Speake now does a rather neat looking piece of solid state kit as a bolt in replacement.
If when back on "flat land" the system is behaving as it should all well and good. What you are seeing may be a pre-cursor to failure but until that happens I suspect it is better to put it to the back of your mind and just do the PSD flush religiously every two years as you should with the brake fluid.
Although my system has been flushed from time to time over the last 11 years, I was surprised when I checked that it was over 3 years since it had last been done. The fluid in the reservoir looked fine, the fluid that came out of the accumulator looked fine, but the stuff in the business end of the unit looked decidedly dodgy [I deliberately collected it in a separate catch vessel to test for this].
In the final analysis it was quite an easy procedure but as with most first time jobs I was a bit concerned about taking such on and the only real difficulty I had was getting the accumulator bleed nipple undone. Then rather stupidly on the final step of the operation I forgot to snap home the pump connector firm and was then faced with a system alarm until I went back in and found my gaff.
Having this list to help with inputs and suggestions was geat for both moral and technical support and wearing good eye protection is a "must".
The lateral acceleration sensor is quite a neat piece of kit but like everything else in the car that has not been replaced it is now 25 years old and most probably has not seen the light of day since since it was made.
As Dave astutely noted, when the car is at an inclination there will be a lateral component of "G" force albeit a very small one. The sensor measures that component very accurately and sends this feedback to the brains [the ABS computer] that reads this signal and the inputs from the wheel speed sensors to compute via a control algorithm an output signal to the PSD system that gives a controlled amount of lock up to stabilise the situation.
Until my recent thread I understood the green light to mean that some corrective signal was being sent to the diff but was advised that it only indicates that there is a condition that needs correcting [if I understood the advice correctly]. This surprised me somewhat but to be fair, no one attempted to correct that piece of advice so I tend to work on the principal that it is the highest level of info available and thus treat it with respect until such time as I have a better reason to believe otherwise.
Either way, it is the PSD system's way of giving the driver some feedback that a condition of some sort exists and hence a caution "to be wary". It would have been more useful if it could have a number advising the amount of lock up signal being applied but it is what it is and in theory should be a vast improvement over the earlier generation mechanical LSD units that are an on/off affair but not everyone thinks that way.
That your signal is going out - presumably after you move off, sugggests that the system is working correctly- whether it is being a bit over sensitive for some reason who knows but sady it is yet another of those "black boxes" that cost a shed load of $$$'s to fix when they go south as invariably they will do sooner or later. I removed my unit, took the lid off the unit - it looked spotless- blew it out with some air and boxed it up again. The sensor has what looks to be a spring arm and a Hall sensor detects lateral movement of said arm. FYI- If it does go south John Speake now does a rather neat looking piece of solid state kit as a bolt in replacement.
If when back on "flat land" the system is behaving as it should all well and good. What you are seeing may be a pre-cursor to failure but until that happens I suspect it is better to put it to the back of your mind and just do the PSD flush religiously every two years as you should with the brake fluid.
Although my system has been flushed from time to time over the last 11 years, I was surprised when I checked that it was over 3 years since it had last been done. The fluid in the reservoir looked fine, the fluid that came out of the accumulator looked fine, but the stuff in the business end of the unit looked decidedly dodgy [I deliberately collected it in a separate catch vessel to test for this].
In the final analysis it was quite an easy procedure but as with most first time jobs I was a bit concerned about taking such on and the only real difficulty I had was getting the accumulator bleed nipple undone. Then rather stupidly on the final step of the operation I forgot to snap home the pump connector firm and was then faced with a system alarm until I went back in and found my gaff.
Having this list to help with inputs and suggestions was geat for both moral and technical support and wearing good eye protection is a "must".
