Technical > Wiring & Sensors

Intermittant operation of P259 output

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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.

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