low speed fan relay stays on after i shut the engine off

[Graham C]

have tried new relay, no change, both fans come on before you start up and stay on when you shut the engine down

 

[Trevor loves holden.]

Is it the vt or vs. Is the key fob making good contact around the ignition slip ring, maybe going into open circuit. Also check your cooling Temperature sensor connection maybe getting bad signal. Did you use Holden relays?

 

[Graham C]

Is it the vt or vs. Is the key fob making good contact around the ignition slip ring, maybe going into open circuit. Also check your cooling Temperature sensor connection maybe getting bad signal. Did you use Holden relays?

yes it is series 1 VT, original factory relay was used,have tested sensor and connection all good, generally if key is bad they wont start, have had it since 2000 and never had this issue

 

[Skylarking]

Not sure about VTs but I thought the BMC controls the signal lines that switch on the fan relays. If so, and the particular transistors within BMC are faulty and stuck on, then when main power is switched on via ignition key, your cooling fans will kick in (and likely stay on until you turn off the car).

It could also be a wiring short between relay and BCM if BCM earths the signal line from fan relay (which is powered (hot) when IGN/ACC turned on).

But I’m also not sure how power is applied to the hot side of fan relay (whether it’s switched or always hot). It would be best if you could get the wiring diagram (fan section) for the VT as that should highlight how power is applied to BCM and to hot side of fan relay. Such wiring diagrams would make the fault finding much easier.

 

[Lex]

Is your coolant temperature sensor wire connected? When not connected the fans will switch on, when motor is started.
Not sure if they will stay on when motor is switched off.

 

[Trevor loves holden.]

yes it is series 1 VT, original factory relay was used,have tested sensor and connection all good, generally if key is bad they wont start, have had it since 2000 and never had this issue

That's correct but if you turn off the car and the key fob is somehow not touching the slip ring then the bcm will think the car is still on keeping power to your fans.

 

[Skylarking]

^ I thought the ignition slip-ring was only used to power(?) and connect the key for the immobiliser handshake process and once the handshake was accepted, the slip-ring isn’t used for anything else? I also thought the ACC/IGN mode is actually set by turning the key though the engine only fires if the immobiliser handshake was accepted (which is why a car can crank but not start).

Maybe the immobiliser / key start description within the VT workshop manual floating about the www could help in understanding this issue...

 

[Trevor loves holden.]

^ I thought the ignition slip-ring was only used to power(?) and connect the key for the immobiliser handshake process and once the handshake was accepted, the slip-ring isn’t used for anything else? I also thought the ACC/IGN mode is actually set by turning the key though the engine only fires if the immobiliser handshake was accepted (which is why a car can crank but not start).

Maybe the immobiliser / key start description within the VT workshop manual floating about the www could help in understanding this issue...

Sends signal to bcm to activate earth to fuse box under the hood I thought, it activates fuel and starter relay earth, once its on you can pull the key out and it will keep running but your light be flashing on the mode settings, this is why it needs to be making contact as you turn it off so the bcm not left in open circuit.. Well that's what I read over the years in different forums maybe wrong.

 

[mirrabucca]

OP Wrote "have tried new relay, no change, both fans come on before you start up and stay on when you shut the engine down"
So they are still running? Or have you disconnected the battery...
How long do they run after you switch the engine off?
If they start up before you start the engine, I assume they start as soon as the key is turned to Ignition?
What happens if you pull out the low speed fan relay at that stage? Do they stop? If not, then there's a short in the fan to relay wiring. If they d stop, then either that relay is faulty, or its being "told" to supply power to the fans. NCM or wiring.
Have you checked DTC's (Diagnostic Trouble Codes)? I do know uner certain circumstances the fans are switched on as a precaution.