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Matt
Matt, Engineer
Category: Volvo
Satisfied Customers: 21374
Experience:  Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
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It's 11pm, you can't really be there... V70, 2003 I think

Customer Question

It's 11pm, you can't really be there...
JA: What is the model/year of your Volvo?
Customer: V70, 2003 I think the radiator fan stays on and drains the battery.
JA: Has the car been overheating? Have you checked the fuses?
Customer: I haven't checked the fuses ... I have never seen the temperature gauge indicating the car was overheating. I have had some problems with the AC ... isn't the radiator fan controlled by some portion of the AC system too?
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: I haven't done anything to it yet other than trying to recharge the battery ... I'm hoping if I can get the car to start then drive it to charge the battery I can make sure the AC system is off and when I shut the car down .... perhaps it won't happen every time ...stupid idea?
JA: Anything else you think the mechanic should know?
Customer: The Check Engine Light comes on intermittently but I don't have the equipment to get any error codes from it.
Submitted: 9 months ago.
Category: Volvo
Customer: replied 9 months ago.
I just wanted to say that my Volvo is an XC70 not the V70 and it is from 2003.
Expert:  Matt replied 9 months ago.

Hello

if you're sure the rad fan is staying on past 30 seconds or so when the engine is stopped then its likely there's a fault with the fan control module located on the back of the fan unit

This cooling fan control module located on the cooling fan frame. The key clue here is that even with the engine off the fan is running, a key indicator that the control module itself has failed. If the fan were to run at key on with a cold engine then the fault could be with the coolant temp sensor or its associated wiring or the A/C pressure sensor and its associated wiring, both of these possible's can quickly be eliminated with a scan tool and access to live data.

In over view the control module receives a permanent live feed via fuse A8, in side the module is a transistor which is a similar set up to the heater blower fan circuit. The ECU monitors engine coolant and at 100deg will send's a pulse width modulated signal to pin 4 at the cooling fan module this signal controls the base current of the transistor and then switches power to the cooling fan. By using a varying signal this can control the speed of the fan without using traditional relays.

The other control circuit that will force the ECU to command the cooling fan on is the A/C system pressure. When the AC reaches 3100Kpa the ECU will command the cooling fan to cool the A/C condenser. This is where live data is useful if with a cold engine key on engine off and live data showing a ECT over 100deg then test the ECT and also its 5v reference voltage and a ground. Likewise under the same condition if you look at A/C line pressure and its over 3100kpa then test the sensor and also its 5v reference voltage, signal voltage and ground.

In this case I suspect the transistor has blown and is creating a direct feed to the fan motor.

Expert:  Matt replied 8 months ago.

Hi

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