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lynall

TD5 air con fan stuck on

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Just noticed the other day when i start my engine the air con fan is running permanently. with the climate set to off ie no air con or internal fan running, only runs with engine running

Not sure how long its been doing this but as i drive with windows up it may have been for ages!

Coolant level is spot on

Coolant is circulating

Gauge reads normal

Sender okay with multimeter set to ohms according to rave specs

Relay okay swapped with one next to it, when pulled fan stops so its getting a signal from somewhere possibly the ecu?

Ta

Lynall

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From the electrical library it would appear to be ECU controlled as you suggest:

"Cooling Fan Description

The cooling fan is located on brackets forward of the radiator. The fan motor is

operated by a cooling fan relay controlled by the Engine Control Module

(ECM). The main relay supplies a feed to the coil of the cooling fan relay. A

permanent feed is supplied to the coils of the main and cooling fan relays

located in the engine compartment fusebox. On V8 models a coolant

temperature sensor is located in the inlet manifold, on Td5 models the sensor

is located in the outlet housing.

The ECM controls the operation of the main and cooling fan relays. At a preset

temperature the ECM receives an input from a coolant temperature sensor

above the values stored in the ECM. The ECM logic enables the earth path for

the coil of the cooling fan relay. The fan motor then gets a feed from the closed

contacts of the cooling fan relay.

When the engine temperature falls, the sensor gives an input below the values

stored in the ECM. When the input from the coolant temperature sensor is low,

the ECM interrupts the earth path to the coil of the cooling fan relay. The

contacts of the cooling fan relay open, this action breaks the feed to the cooling

fan motor, and the motor stops. The cycle will start again when the engine

coolant temperature rises and the sensor sends a high input to the ECM.

The ECM has an engine off function, when the ignition is turned off the ECM

logic goes into a watchdog routine and monitors the coolant temperature for

approximately seven to ten seconds. If the coolant temperature is still high,

over 100 C (212 F) V8, 110 C (230 F) Td5, the ECM logic can control the

operation of the fan motor.

On V8 engines the ECM will only enable the fan if the inlet air temperature is

over 60 C (140 F). The ECM will allow the fan to run for a maximum of ten

minutes, however the ECM continues to monitor the coolant temperature. The

ECM logic will stop the fan if the coolant temperature is below the acceptable

values stored in the ECM. To prevent a flat battery, the fan will be stopped

(regardless of coolant temperature) if the battery voltage falls to 12 V.

Cooling Fan Supply

Circuit supply

A permanent feed from the battery positive terminal is connected by an R wire

to the engine compartment fusebox. A feed from this wire is connected to the

contacts of the main relay and also to fuse 13. The feed passes through fuse

13 and to the inertia switch on a NB wire. The feed from the inertia switch flows

on a WG wire to the engine compartment fusebox and is connected to the coils

of the main relay. in this condition the coil and contacts of the main relay

receive a permanent supply.

The permanent feed from the battery on a R wire to the engine compartment

fusebox is also connected via fusible link 1 to fuse 5. From fuse 5 the

permanent feed is connected to the contacts on the cooling fan relay. In this

condition the contacts of the fan relay receives a permanent feed from the

battery via fuse 5.

Main relay - ignition supply

When the ignition switch is a position II, the ECM switches on the earth path for

coil of the main relay. Current flows through the coil of the main relay and flows

on a UR wire to pin C0635-23 V8/C0658-21 Td5 on the ECM. With the coil of

the main relay energised the main relay contacts close, power is now available

to the coil of the cooling fan relay, via the closed contacts of the main relay.

Cooling Fan Operation

V8 engine

The engine coolant temperature sensor sends an input on a G wire to pin

C0636-22 on the ECM. The engine coolant temperature sensor is earthed on a

RB wire to pin C0636-21 on the ECM.

When the coolant temperature is high, the value of input from the coolant

temperature sensor causes the ECM logic to switch on the earth path for the

coil of the cooling relay, on a GW wire to pin C0636-31 on the ECM. With the

coil of the cooling relay earthed the coil is now energised. The cooling relay

contacts close and current flows on a BN wire to the cooling fan motor.

Td5 engine

The engine coolant temperature sensor sends an input on a KG wire to pin

C0158-7 on the ECM. The engine coolant temperature sensor is earthed on a

KB wire to pin C0158-18 on the ECM.

When the coolant temperature is high, the value of input from the coolant

temperature sensor causes the ECM logic to switch on the earth path for the

coil of the cooling relay, on a BP wire to pin C0658-4 on the ECM. With the coil

of the cooling relay earthed the coil is now energised. The cooling relay

contacts close and current flows on a BN wire to the cooling fan motor.

All models

The current flows through the cooling fan motor to earth header C0018 on a B

wire. The cooling fan motor will operate as long as the ECM receives a high

signal input from the coolant temperature sensor. When the coolant

temperature is low, the ECM logic interrupts the earth path to the coil of the

cooling relay. The contacts of the cooling fan relay open, the fan motor power

supply is now broken and the motor stops. The cooling fan will cycle on and off

as the coolant temperature rises and falls."

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Today using a power probe i have sussed that the relay is getting an earth from the engine ecm (ecu) so causing the fan to run.

But i cant suss what is causing the ecu to think the fan needs to run1

I have done a check on the climate ecu and it shows no faults.

The coolant fan relay is getting an earth signal but not the air con pump relay so i am pretty sure the signal is from the engine ecu and not the climate ecu.

Rave tells me if the coolant temp sensor fails the ecu will work out the temp from the fuel temp sensor as a back up.

Which is a bit of a tosser as i am not sure what is at fault the ecu or a sensor telling the ecu to run the fan.

Lynall

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Check pin 9 from connector C0793 on AC ECU which is "Cooling fan request" to ECM. That way you will know which one issues the command for the fan to come on, AC ecu or ECM ecu.

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Right done some more testing with trusty multimeter and have found the following:- the ac ecu is switching as its meant to for the cooling fan control pin 9, the engine ecu is supplying an earth path to the fan relay as soon as engine is started black plug pin 4.

Not sure if its faulty ecu or the ecu is getting a signal from a duff sensor thats saying its hot run that bloody fan!

Any ideas?

cipx2 thanks for the pin info on the ac ecu.

Bogmonster thats a pretty extensive description! have checked all wires can see no damage, everything switchs as it should.

I have even put std chip back in ecu on the off chance but no difference.

I just know its something stupid (prob me) but am not sure what.

Only thing i have changed recently is the fuel pressure regulator which came with a new sensor this also checks out with multimeter according to Rave.

Thanks for the replies and info much appreciated

Lynall

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The answer is simple, folks. Your ECU has sensed that at some time your engine was overheating. It then switches the aircon fan on to help out. Unfortunately it will not switch it off again until the fault is cleared using a pooter. We do this all the time here, although maybe the ambient temps don't help. It is a not-really-helpful feature of the ECU. We clear the faults for free, but apparently LR stealers charge a lot just for doing this. Well, it helps pay for the tiled workshop floors and all the gear the mechanics wear.

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Hey you two thanks for that, i would never have thought of that.

Amazing and maybe a cheap fix?

Lynall

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Interesting - never heard of that before but then overheating is not a big feature of our day here :lol:

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Nor ours at the moment as it has been raining and cold (10c) for a few days now.

We have 3 overheated TD5s in the workshop at the moment.... Luckily none of them seem to have a cracked head or block, so we can get away with the gasket, hopefully.

TD5 cylinder heads are unfortunately only available from LR here, which makes them ridiculously expensive, often about as much as the vehicle is worth. The only thing to do in that case is to fit a second hand engine from a rolled vehicle. And there are a few of those around.

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On 10/8/2007 at 5:27 PM, JimAttrill said:

The answer is simple, folks. Your ECU has sensed that at some time your engine was overheating. It then switches the aircon fan on to help out. Unfortunately it will not switch it off again until the fault is cleared using a pooter. We do this all the time here, although maybe the ambient temps don't help. It is a not-really-helpful feature of the ECU. We clear the faults for free, but apparently LR stealers charge a lot just for doing this. Well, it helps pay for the tiled workshop floors and all the gear the mechanics wear.

Hi,

I have the same issue and I have taken my car to the dealership twice and they had no idea about this issue. I got them to hook it up to the system called T4 which apparently is LRs genuine diagnostic system for the TD5. However, I tried going through the menus but couldn't find any option to turn the fans off.

If anyone here is familiar with this system, can you please guide me going through what menus will lead me to an option to turn this forced assist off.
You help is much needed and would be really appreciated!!

I am from Pakistan and the TD5 Defender was never launched here but the dealer has some experience with TD5 Discos.

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The Nanocom diagnostic box can do it, but it wouldn't surprise me if the OEM one couldn't.

Maybe consider buying a Nanocom, if you intend keeping the Landy, better, too, if you have mates who have vehicles with OBD-II connectors, because all you will need then is to buy the software and the appropriate cable for the various models, and you can start making some side money doing diagnostics.

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