Intermittant operation of P259 output

[dnb]

I'm a little confused about this...

I noticed that one of my fans was not working correctly, the cause was the drive relay (fed from P259 output no 6) chattering.  Swapping the relay made no difference to operation, and swapping the fan and water pump (fan 1 and fan 2 on my car) outputs over in software didn't change the problem either.

I therefore assume it's a hardware problem with my P259 chip.  Has anyone had one fail in this way?  The other P259 outputs - I use most of them - all seem to work properly. 

Needless to say I would prefer to avoid needless rework of the circuit board.

Thanks

[rob@vems.co.uk]

Thats a new one on me, are you sure that there's no other control function set for that pin?  They might be fighting each other turning the channel on and off.

[dnb]

That's exactly what I thought Rob.  Unfortunately I couldn't find anything...

It could be a firmware bug - I am using one of the new alpha builds after all.

[rob@vems.co.uk]

It doesn't seem like the sort of fault you get with semiconductors, they tend to work or not work...
Its almost worth reverting and seeing if the problem persists.

[dnb]

I will revert to 1.0.73 when I get a chance.  That's the last time I remember it being OK.

[Bat]

Hi,
Low voltage causes relay chatter have you checked the winding feed?
Are you using the VEMs loom with relays?
Cheers,
Gavin

[dnb]

Not using the VEMS loom because it didn't exist when I did this install.  I made my own loom with parts from Vehicle Wiring Products.

Feed looks to be good to the relay, but it could always be a high resistance connection in the fuseboard.  I was hoping to avoid pulling the fuseboard out this month, but I ought to check.

[Bat]

Hi
You could try scoping the VEMs output or stick a test light between a good pos and the VEMs output and see if it flickers for a lo-tech test
Cheers
Gavin

[peter_jensen]

I have seen the same thing on a consumer car using 1.0.36 but we haven’t got time to analyze the problem. Maybe you could tray connect a proper – to the relay and see if the chatter stops.

Peter

[dnb]

I think I found a solution...  I will try to explain it, but it may not be clear.

The temperature sensor is a non-linear device - the resistance of the sensor varies exponentially with temperature, so a lookup table is used to linearise the input for the ECU.  This means that at the steepest part of the resistance/temperature curve (the most useful bit in my case), a large temperature change might only cause a single bit change in the A to D converter. 

So, given that there might be a bit of noise in the readings, a single bit change in the A to D may in fact be a larger temperature than the hysteresis parameter for the fans.

So I increased the hysteresis until the problem went away.  It is now 4 degrees instead of 3 and no sign of the bad behaviour.

[Bat]

Hi,
Sorted. Easy fix too
Cheers,
Gavin