Michael White

Good evening everybody. Apologies for my first post being one asking for help but I’m out of ideas and although I’ve found mention of similar faults I can’t find anybody that’s stated a cure. Here is my issue and I’d really appreciate any help.

Everything was fine un until a week ago. I stopped at the services after a 4 hour drive (240 miles) and everything had been fine. The car was parked for one hour before I set off again. I then noticed, as I got stuck in traffic in Birmingham that the temp was low and the cooling fan was running on full speed. The fan continued running on full speed for the full 60 miles back home. When I got home and switched off the car the fan stopped but as soon as I turned the ignition back on the fan roared back in to action. I checked everything I could see (wires for damage, plugs for security) but couldn’t find any issues. However, when I then turned the ignition back on the fan didn’t run. About 1 hour later I went outside and all I could hear was my cooling fan switching on, running up to speed, switching off and the cycling again. The only way I could stop the fan was to unplug it.

Unfortunately I needed my car during the week to get to work. I left the fan unplugged, turned off the AC and drive the car keeping a very close eye on the temp gauge. It ran at the temps you’d expect and only started getting hot when stuck in traffic (I didn’t let it get over 95degrees). I then decided today to plug the fan back in to see what happened. To my surprise everything worked perfectly. With the AC on the fan would run on and off at a low speed and no big roaring noise from the fan running at full speed. I left it running for about 15 minutes and then switched it off. I then parked it up for about 5 hours with no issues (I was outside all this time so I know it was fine). I then went to the shop in it (3 mile round trip) and parked it back up again. Just before it had been parked for 3 hours I suddenly heard the cooling fan switching on and off and continuously cycling on and off. I’ve now had to go and unplug the fan again to stop it flattening the battery.

Sorry for the long long post but has anybody else had this issue and managed to find the cure?

Thank you in advance.

Michael

Mud

Hi Michael and welcome.
Do you have access to any sort of scantool that's beyond a generic obd2 type? I would be curious to see what the ecu is commanding to the fan control module. Obviously the fan is receiving power since it's running, but could be something simple like a bad/shorted fan relay.
I mentioned the ecu module as I was thinking to verify that the various inputs the ecu is seeing are correct, such as ac, engine temp, etc. If the inputs are correct then the next item to check is the fan module (not sure on cdi, on my gas engine it's on the fan). But the first easy check is the fan relay.

Michael White

Thank you for the reply.

Unfortunately I’ve currently only got generic scan tools, but I did order an icarsoft V2 last night which will be here later in the week. I’m guessing the relay is what I've currently unplugged. It appears to be part of the fan cowling with a big plug going to it with two thick wires (to power the fan) and two thin wires (to power and trigger the relay). I’d convinced myself it was going to be the AC pressure switch sending a high pressure reading therefore causing the fan to run on full speed. However, I’m not sure this would be the case to make the fan suddenly start running after it’s been parked for nearly three hours, following just a 2 mile journey.

I’ve read somewhere that the ECU, behind the driver’s wheel arch, can suffer from water ingress. I’m wondering wether to remove and check that today to see if I can see anything. The other thing I thought about was unplugging the AC pressure switch but I’m not sure if this will default to a low or high pressure value. I have already checked all the wires and plugs I can find for signs of damage or corrosion.

Thanks,

Michael

Mud

Without a wiring diagram in front of me, I believe that's the fan module you described but I would also want to verify power/ground/control circuits. Also if there is a relay located in the underhood fuse box.

Speaking of diagrams, a great item to have is the WIS/EPC for these cars. Includes factory manual work instructions, parts ID, diagrams, etc. CD under $20 on eBay but it's a huge file, something like 35gig. I keep it on a dedicated "garage" laptop and have used it a lot.

Your approach on control circuits sounds very logical - I hope you post further progress as you go further.

Edit - upon further mulling over this, I can't say for sure on the cdi but on my V6 the front F32 pre-fuse box contains a primary power feed for the fan. There is also a fuse (no relay) in the underhood fuse box. As mentioned I think these are ok in your car (never hurts to check though) since the fan is able to run on both low and high speeds. I believe that the relay is contained within the module located on the fan, so if you are able to verify that control to the fan module is good then it seems the module itself may have an internal short. In the past I would install a new module and hope for the best but these days I try to actually diagnose the problem before buying parts. Even if I had 50 cents back on every dollar spent like that I'd be happy lol.
Good luck.

kajtek1

The fan has module that takes signals from
1 AC controller
2 engine temp sensor.
So either one of those 3 items can act and with electronics, you can either keep replacing parts, or get the scanner.

Michael White

Thank you both for taking the time to reply. I have spent a couple of hours looking in to the problem today. I have removed the AC pressure switch connector and cleaned it (I couldn’t see any issues). I’ve also removed the ECU from driver’s side wheel arch to check for any water ingress etc, but agin no issues. I’ve cleaned all the connections and replaced the ECU. I then started up up whilst the front was still up on axle stands and left it idling for about 20 minutes and it behaved itself.

Its now been parked up for up for the last 4 hours and the fan hasn’t come on yet. I’ve also ordered an icarsoft V2 to check as much data as possible (my generic scan tool hasn’t found any faults) and c do for any faults. I’ve also ordered the AC pressure switch and arranged for a mobile AC guy to come and evacuate the AC system later this week and then wait whilst I fit the pressure switch so he can then re-gas it. Im hoping that the issue is that the pressure switch has gone faulty and is telling the ECU that the AC pressure is too high, therefore putting the fan on to avoid compressor damage. I’m hoping the icarsoft V2 will arrive early this week so I can read the AC pressure value before I replace the switch (does anyone know if the icarsoft V2 will read the pressure?).

I will update the post once I've been able to plug in the icarsoft V2 and I’ve replaced the pressure switch.

kajtek1

Why would you spend time and money replacing pressure switch without troubleshooting?

Mud

I agree with Kajtek.
An ac pressure switch operates off of reference voltage. Say it receives 5v reference from ECU, the return voltage designates system pressure to the ECU. It's entirely possible that the pressure switch is defective but that's not been verified. If the switch is defective and returning incorrect voltage the ECU could be thinking high speed fan is needed when it's actually not required. I understand it's a low dollar guess but you should be able to verify voltage using the scanner or even using a backprobe with digital voltmeter. However, you need a wiring diagram to know what wire is what.

Oda112

Check the CTS (coolant temp sensor) and the wiring to/from it. In most cases when the cooling fan stays on after engine shutoff and there are no codes present that's the fault. This little 17$ part fails in a weird way, intermittently. It will not throw actual DTCs until it is completely dead. Mine was doing the same for months, went away after I replaced the sensor.