Peugeot 407 Cooling problem

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Joined: 17 Jul 2019, 18:24

Peugeot 407 Cooling problem

Post by lulupapa »

Hi guys!

I ned Your help, I am not sure 100% what could resolve my problem.

Firstly the parameters of my car:

Peugeot 407 sedan
2.0i RFJ (EW10A)

About the issue:
The cooling fan does not kick in at low speed at all. The high speed operates as expected.
I checked the car with diagbox, no fault codes.
I tried to test if I can turn on the low speed with the diagbox, but without any success. However during the highs peed test the cooling fan kicks in as expected.

When I turn on the A/C the pressure switch clicks and the cooling fan start operating.
I checked also the measured engine temperature and the cooling fan speed command field.
When the A/C is on, the cooling fan speed command value is about 50-60%.
When the A/C is off and the engine coolant temperature is above 98°C the cooling fan speed command field in the diagbox shows 0%, and the low speed does not kick in :(
When the engine coolant temp reaches 111°C, the high speed fan kicks in and keep operating for about 10-20 sec.
When the engine coolant temp is above 105°C, after turning off the engine it does not kick off the low speed to cool back the engine.

I also checked in the ServiceBox when should kick in the low and the high speed stage of the cooling fan:
low speed at 98°C
high speed at 105°C

I checked the connectors around the cooling fan. the connectors and the relay seemed to be OK, no corrosion at all.
The wiring diagram is attached here:

I assume the fuse Nr. F1 and MF01 are fine as well as the relay, because the cooling fan kicks in at high speed and when the A/C switched on.

I measured the control signal coming from the motor controller using an oscilloscope.
I checked the control wire (Nr. 1540) coming from the motor controller to the fan's controller. The control signal is PWM. When the high speed test was running from the diagbox, I saw a correct PWM signal on the control wire. When I turned on the A/C the result was the same.
Now the interesting part, when I run the low speed test with the diagbox, there was not any PWM signal on the control wire (Nr. 1540). Very interesting.
And the most interesing thing is when the engine temp reaches 98°C, the motor controller doesn not send an increasing PWM signal to the cooling fan controller (commanding the ecu of the cooling fan to start spinning), neither at 108°C. It only sends almost a full PWM signal to the fan when the motor temp reaches 111°C.

I assume the cooling fan is fine as well as the wiring loom. There should be some isse with the motor controller itself.
Can't figure out why does not send the motor controller control signal to the cooling fan above 98°C.

What do you think?

Is it possible to fail the motor controller in this way?

Is there any chance to replace the motor controller with an used one?

I would really appriciate if You could help me with your knowledge and experience.

Thank You for reading this post and for making effort to help me out :)

Best regards,