Hi speed cooling fan trouble

[Brett_jjj]

Ive already tried removing the temp sensor wiring with the engine running a few times now for the test you mention,the fan starts as normal after approx 12 seconds ,but doesnt change to hi speed like its meant to approx 6 seconds later.I just dont know,Ive used different relays,the fan works on both speeds when jumpered to the battery,theres no fuses or fusible links blown,the fan switches on with the AC no worries,and also switches on when temp gauge gets to half,which is normal for it to do.and no wiring has been disconnected or tampered with.And lastly when the fan is commanded on with a tech 1 the low fan speed works,but the hi fan speed doesnt.

 

[Cheap6]

If instead of connecting a jumper wire from the 86 pins to earth you use a test light or voltmeter you will be able to see if the switching side is OK or not. There should be battery voltage at the 86 pins with the relays not being switched by the PCM or BCM, ignition on for high speed, no voltage with them switched via either Tech 1 or fooling the coolant temp input.

If the voltage drops with the switching, the fault is on the switched side (or in the relay but you've already checked that by swapping it).

If the 86 pin voltage at the relay doesn't drop, look for the voltage (+ drop) at the PCM terminal. If it's got the voltage but not the drop it's in the PCM. No voltage is a broken wire.

If you need to ID the 5 pin relay pins, 30-87a has continuity across it (open circuit when switched), 30-87 is open circuit (closed circuit when switched), 85-86 should have a resistance of ~75 ohms or so. Pin 85 is the one with power to it (to differentiate between 85 and 86).

Theres 12v available to pin sockets 86 and 30 with the key on, on the hi speed relay.With key off there is 12 v available at pin socket 30 only.

If there is power to the 30 terminal on the high speed then jumping that to the 87 terminal should turn the high speed on. If not then the wire from the 87 terminal is not reaching earth. That should be spliced into the same wire that earths the low speed winding so the fault would be between the splice and the relay terminal (the low speed switching works).

 

[Brett_jjj]

Thanks mate, Im going to have another go at it this morning,some lowlife knocked off the spare VS fan I had,so I cant check that,although this one Im using showed up fine when jumpered to the battery.

 

[Brett_jjj]

The terminal 86 has 12v available with the hi speed off,when hi speed is commanded on nothing changes with terminal 86,it stays at 12v.

 

[admir87]

one of the terminals always has 12v, its the constant, with engine on

that might be the 86

its the signal terminal that will get 12v when the fan is commanded to come on, but dont know without looking which terminal it is

 

[Brett_jjj]

Ive tried what cheap6 said about terminal 86 dropping voltage once the Hi fan is commanded on.It just stays at 12 v.Theres no change at all.Has anyone know of anything else I can try,this is really p*****g me off.If theres no hi fan signal from the ECU I guess that the next step is to try another ECU,Does anyone know how much a wreckers would want for a VS V6 auto ECU.

 

[Cheap6]

Before you replace the PCM, what happens on the wire for high speed fan switching at the PCM end. The PCM may be working OK and switching the terminal to earth but the wire or a connection to it may be the problem.

On a VT the terminal is F6, the wire is blue with a white trace. VS may be different but from my experience there is a lot the same as VT.

There is more than one way to check the same thing: Using a low current draw - less than 300mA when connected across the battery - test light connected to battery voltage and to the PCM terminal (F6 or VS equivalent) that is switched to earth should also tell you if it is working or not. The test light should come on as the earth transistor is switched inside the PCM.

 

[RX25SE]

^^^ as above. Use and LED test lamp.

 

[Brett_jjj]

Blue/white trace wire at the ecu end tests the same as the terminal 86 where the relay goes,there is no change when the fan is switched on.It just stays the same.The test light stays lit.Is this wire meant to drop its voltage when the fan is switched on?Also in the Gregorys manual it says that the cooling fan will constantly run on hi fan if the ECU is in limp home mode,how can I make the ECU go into limp home mode to see if the hi speed comes on them?

 

[Brett_jjj]

I just rechecked it all and the blue/white trace wire goes to pin 85 on the hi speed(large)relay not 86.It was difficult to see exactly which terminal it was going to,.but anyway it is showing 5.25 volts at the relay terminal and at the ECU.It doesnt change when the hi speed fan is commanded on and off,Its just staying at around 5 volts.