Fiat 500 1.4 2007 on...

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Fiat 500 1.4 2007 on...

Postby Technician » Tue Jun 20, 2017 8:01 pm

Interesting problem appeared on the above cars cooling system. The customer advised the engine overheats, someone has already established that the radiator cooling fan is not receiving a live supply. Referring to the wiring diagram I concluded that there are two relays fitted, a low speed and high speed for the fan. I checked the electrical circuits through and have found that the ECM is not grounding pins 12 and or 13, hence the fan does not operate, but if grounded the fan circuit works OK.

I ran the engine from warm to hot and observed that the cooling system temperature sensor is working OK and can see the temperature reaches up to 120 degrees C, at that point I shut the engine off as there was no possibility the cooling fan was ever going to activate.

The wiring diagram does not lead me away from the engine management system but I kept asking myself, what then triggers the engine management ECM to ground pins 12 and 13!

Looking deeper into this I ended up at the Air Conditioning system wiring diagram, there I can see the engine management ECM, in brief there is the air con A/C refrigerant pressure sensor, which looks like a potentiometer by visual description, the coolant temperature sensor, and CAN L and CAN H.

The CAN L and CAN H are connected to the multi-function control module, however this is were I seem to ask the question, what data signals should I see on the CAN system!

Maybe common sense should not come into this, but if the A/C system was discharged and the CAN system had signals/data missing, I would have thought for safety reasons these areas should not prevent the cooling fan operating when the engine temperature becomes too hot, i.e. outside of the operating safe range.

Any thoughts on this!
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Re: Fiat 500 1.4 2007 on...

Postby STC » Thu Jun 29, 2017 12:17 am

What scanner are you using ?

moving on
A/C refrigerant pressure sensor, which looks like a potentiometer by visual description,


More likely a "Wheatstone Bridge" than a simple potentiometer.

From a Diag point of view, get the PCM to run the fans first, TCU & HVAC will follow.
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Re: Fiat 500 1.4 2007 on...

Postby Technician » Thu Jun 29, 2017 12:31 am

Thanks for replying STC

I didn't use the scanner, but you know I have the VERUS. Must admit STC the AD wiring diagram showed a potentiometer and nothing like a wheatstone bridge, the latter looking like a bridge rectifier made up of four diodes, but is constructed using four resistors, the potentiometer having three connections, one input through to ground along with a varying output terminal.

There is a clear difference between a bridge rectifier and a wheatstone bridge, just so we are singing from the same hymn sheet :wink:

Sorry I might of worded the original post incorrectly where you pointed out I said the refrigerant pressure sensor looked like a potentiometer, clearly they don't look the same, I'll double check the wiring diagram for confirmation, sorry my bad on this point.
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Re: Fiat 500 1.4 2007 on...

Postby victor2k » Thu Jun 29, 2017 7:30 am

Hello,
Try to perform the active test on cooling system (ECM must give you this option).
A/C based on the measured pressure will send a signal to turn on(on a low speed) the cooling fan but will not block the engine cooling.
Regards.
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Re: Fiat 500 1.4 2007 on...

Postby STC » Thu Jun 29, 2017 5:03 pm

There is a clear difference between a bridge rectifier and a wheatstone bridge, just so we are singing from the same hymn sheet :wink:


Some (VAG, Merc ...) Will use a 3 pin component to send both Pressure & Temperature on the same wire. However, if you can see 120c then clearly the issue is ECU, Wiring, Relay or Fans ?

How many pins in the ECT ?
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Re: Fiat 500 1.4 2007 on...

Postby Dcunning35 » Thu Jun 29, 2017 5:07 pm

The resistors can fail.on the ka ,same family of powertrain and management as 500 , from memory this stops fan running , but fans also suffer from corrosion too.
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Re: Fiat 500 1.4 2007 on...

Postby Technician » Thu Jun 29, 2017 8:48 pm

STC wrote:
There is a clear difference between a bridge rectifier and a wheatstone bridge, just so we are singing from the same hymn sheet :wink:


Some (VAG, Merc ...) Will use a 3 pin component to send both Pressure & Temperature on the same wire. However, if you can see 120c then clearly the issue is ECU, Wiring, Relay or Fans ?

How many pins in the ECT ?


The fan works OK the problem being the ECM is not grounding the relays. What I don't know is what tells the ECM to ground the relays!

The ECT is a two pin.
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Re: Fiat 500 1.4 2007 on...

Postby STC » Fri Jun 30, 2017 12:39 am

What I don't know is what tells the ECM to ground the relays!


ECT would be one for sure.

Do we have a feedback signal issue here ?
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Re: Fiat 500 1.4 2007 on...

Postby Dcunning35 » Fri Jun 30, 2017 10:44 am

Ect is the input for fan control , is this not just an in acurate ect reading , thermostat housings crack . If your in doubt use a potentiometer to mimick ect signal , this will prove pcm ,relays ,fans .
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Re: Fiat 500 1.4 2007 on...

Postby STC » Fri Jun 30, 2017 11:32 pm

Could an out of range resistance across the coil of either Relay / or current consumption be paralysing it ?
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