Technical No. 1 fan fault

[Rich98]

I have a citreon relay same as fiat ducato 2.2 2008 the no 1 fans not working comes up on Dianostic as po480 code. Says oc or sc earth(-) can any one help in we're I start to look for the fault

 

[moodrater]

Check for open circuit or short circuit to earth.?? Seriously though get out the multimeter and chase it back. check relays, wiring, fuses, check if fan is seized or shorted.

 

[andyk0001]

I have a citreon relay same as fiat ducato 2.2 2008 the no 1 fans not working comes up on Dianostic as po480 code. Says oc or sc earth(-) can any one help in we're I start to look for the fault

I have a similar problem on a 2021Ducato 2.3. The diagnostics say short to earth on left fan(looking from front), this is controlled by Relay 07.When checking with multimeter there is a 160 ohm resistance to earth with the fan disconnected and relay out
However, this is uni-directional ie a diode effect to earth.Is there a diode in the circuit somewhere? The diode is reversed biassed.

 

[Communicator]

I have a similar problem on a 2021Ducato 2.3. The diagnostics say short to earth on left fan(looking from front), this is controlled by Relay 07.When checking with multimeter there is a 160 ohm resistance to earth with the fan disconnected and relay out
However, this is uni-directional ie a diode effect to earth.Is there a diode in the circuit somewhere? The diode is reversed biassed.

The diode effect may be due to corrosion. (Many years ago copper oxide rectifiers (diodes) were common, then came selenium rectifiers, germanium diodes, and now we have silicon diodes.)

See Reg 65's post in this thread. Just a thought, but could the so called "rusty junction" or similar, be the cause of your problem?

 

[andyk0001]

The diode effect may be due to corrosion. (Many years ago copper oxide rectifiers (diodes) were common, then came selenium rectifiers, germanium diodes, and now we have silicon diodes.)

See Reg 65's post in this thread. Just a thought, but could the so called "rusty junction" or similar, be the cause of your problem?

Thank you.Something along those lines did cross my mind.The advice in Reg 65's post is work checking.

 

[andyk0001]

I have a similar problem on a 2021Ducato 2.3. The diagnostics say short to earth on left fan(looking from front), this is controlled by Relay 07.When checking with multimeter there is a 160 ohm resistance to earth with the fan disconnected and relay out
However, this is uni-directional ie a diode effect to earth.Is there a diode in the circuit somewhere? The diode is reversed biassed.

Further to the above. I have now checked the right fan(looking from front).There is a reversed biassed diode also showing 160 ohms but on the 12V input to the relay(06), whereas on the left fan(relay 07) it is showing on the output of the relay to the fan.This does not seem very logical, surely one would expect the diode to be in the same part of the circuit for each fan.

 

[Communicator]

Both fan relays are operated by the ECU, on the negative side, so looking towards the ECU you would expect to see an output transistor or similar device.
The Bosch convention for vehicle electrics has terminal 86 of the relay as positive. For confirmation inspect any diode fitted relay/advert. Diode is reverse biased with 86 positive, otherwise "phutt" (blown fuse).
On my x244 and I suspect on other models, Fiat do not follow the Bosch convention, and relay coils can be connected in either polarity. I recently checked my engine bay fusebox, and have recorded T06 as having 86 positive, but T07 has 85 positive. Fiat standard relays use a resistor in parallel with the coil for back emf supression., so no polarity issues.

I am wondering whether these inconsistent polarities are causing confusion?

Do you have a circuit diagram? I have a copied one for the x250. Quite basic, no diodes shown. Can attach on request.

A diode would have a forward drop of at least 0.4V. Fans draw considerable current, being fused at 40A to accommodate starting surge.
Assuming a running current of 10A, diode would dissapate 4W. May not seem much, but consider a small tungsten bulb. They get rather too hot to touch.

 

[andyk0001]

Terminal 30 of Relay O6 connects to the +12V and also to the diode.
However on Relay 07 it is Terminal 87 that connects to the diode and the fan.

Does anyone know how the ECU checks a cooling fan.On our MOHO, diagnostics show a short on Fan No 2.How does the ECU 'know' there is a short-what is it measuring?

 

[Communicator]

Terminal 30 of Relay O6 connects to the +12V and also to the diode.
However on Relay 07 it is Terminal 87 that connects to the diode and the fan.

Does anyone know how the ECU checks a cooling fan.On our MOHO, diagnostics show a short on Fan No 2.How does the ECU 'know' there is a short-what is it measuring?

I suspect that the ECU is only monitoring the relay coils, but I have not proved thas. There areconnectors close to the fans, so if you disconnect one fan, what does the ECU detect repor?

 

[Mike1alike]

I think there should be a thermal fuse on the fan. Check that out, it's probably burned.

 

[andyk0001]

Thanks for responses.

I have checked from relays 07 and 06 to the fans no short circuits. Both fans run when 12V applied to relay sockets using a wire link.Both relays change over and seem perfectly ok.
I agree that logically relay coils would be monitored from the ECU.
I have no OBD scanner at present but will get Multiecuscan once I find the Security Gateway Module which Gendan assures me will be fitted somewhere, then I can initiate fan operation from the OBD.

 

[andyk0001]

Both fan relays are operated by the ECU, on the negative side, so looking towards the ECU you would expect to see an output transistor or similar device.
The Bosch convention for vehicle electrics has terminal 86 of the relay as positive. For confirmation inspect any diode fitted relay/advert. Diode is reverse biased with 86 positive, otherwise "phutt" (blown fuse).
On my x244 and I suspect on other models, Fiat do not follow the Bosch convention, and relay coils can be connected in either polarity. I recently checked my engine bay fusebox, and have recorded T06 as having 86 positive, but T07 has 85 positive. Fiat standard relays use a resistor in parallel with the coil for back emf supression., so no polarity issues.

I am wondering whether these inconsistent polarities are causing confusion?

Do you have a circuit diagram? I have a copied one for the x250. Quite basic, no diodes shown. Can attach on request.

A diode would have a forward drop of at least 0.4V. Fans draw considerable current, being fused at 40A to accommodate starting surge.
Assuming a running current of 10A, diode would dissapate 4W. May not seem much, but consider a small tungsten bulb. They get rather too hot to touch.

Would appreciate the diagram.Thank you.

 

[Communicator]

Would appreciate the diagram.Thank you.

 

[andyk0001]

Great thanks.