High/low switch

Evening all, TD5 Defender with a D2 transfer box. We suspect the high/low maps are wrong as my Defender is undriveable in low(very sharp throttle response) and Nanocom is showing high/low correctly which they regularly don’t.

is it just a case or putting the plug on the switch on the other way around or is there more to it?

Anyone any ideas or done it before??

I didn't want to answer yesterday incase I looked stupid lol!
I'm also not familiar with the td5 or a D2 transfer box.
Buuuuttt...isn't the transfer box all mechanical?
How could an engine(I presume) remap affect the TB?
Throttle response will be sharp in the low range, for example, tickover is all that is required for 1st low. I can reverse off my mates 35 Deg drive on tickover in low box.

Flossie said:

I didn't want to answer yesterday incase I looked stupid lol!
I'm also not familiar with the td5 or a D2 transfer box.
Buuuuttt...isn't the transfer box all mechanical?
How could an engine(I presume) remap affect the TB?
Throttle response will be sharp in the low range, for example, tickover is all that is required for 1st low. I can reverse off my mates 35 Deg drive on tickover in low box.

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I think the only purpose of the switch is to dull down the throttle response in Low range. Early TD5 vehicles I believe were not fitted with the switch, which came in around 2002/3

tom1979 said:

Evening all, TD5 Defender with a D2 transfer box. We suspect the high/low maps are wrong as my Defender is undriveable in low(very sharp throttle response) and Nanocom is showing high/low correctly which they regularly don’t.

is it just a case or putting the plug on the switch on the other way around or is there more to it?

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TD5 ECU's change the throttle response when in low box - that is why there is a low position detection switch.

If you unplug the transfer box on a TD5, put it into low, then drive it it, it will be as you describe. The TD5 normal road throttle response can tear the drive train apart in low range - that is heresy but makes sense.

discomania said:

TD5 ECU's change the throttle response when in low box - that is why there is a low position detection switch.

If you unplug the transfer box on a TD5, put it into low then drive it it is as you describe. The TD5 normal road throttle response can tear the drive train apart in low range - that is heresy but makes sense.

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I understand that, what I need to do is reverse the setup as I think my ECU is reading it the wrong way around. Can the switch just be put on the wrong way around to correct it ??

tom1979 said:

I understand that, what I need to do is reverse the setup as I think my ECU is reading it the wrong way around. Can the switch just be put on the wrong way around to correct it ??

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It can't read the wrong way round - the switch is just contacts open/contacts closed. Reversing the wiring will do nothing. It sounds to me like the ECU is not detecting the signal - or it's not connected or the switch is shot. Try linking out the contacts on the plug and then try it with the contacts open on the plug and see if you can get the throttle response to change.

Does it drive OK in hi? If so then the maps are not reversed, it is just not going into low box map.

discomania said:

It can't read the wrong way round - the switch is just contacts open/contacts closed. Reversing the wiring will do nothing. It sounds to me like the ECU is not detecting the signal - or it's not connected or the switch is shot. Try linking out the contacts on the plug and then try it with the contacts open on the plug and see if you can get the throttle response to change.

Does it drive OK in hi?

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this is what we’re wondering, if perhaps the throttle response in high is dulled down

tom1979 said:

this is what we’re wondering, if perhaps the throttle response in high is dulled down

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Wait - you say Nanocom is detecting the change? Then the ECU knows fine.

It would not surprise me if Land Rover did something differently between Defender and Disco TD5/Transfer box setups - to the point that I wonder if there is some sort of incompatibility. When you removed the old T-case what connector was on it? Did they look the same? Did it work fine before you changed them?

There you go!
Now I look stupid

discomania said:

Wait - you say Nanocom is detecting the change? Then the ECU knows fine.

It would not surprise me if Land Rover did something differently between Defender and Disco TD5/Transfer box setups - to the point that I wonder if there is some sort of incompatibility.

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I have a discovery NNN ECU too though...

Flossie said:

There you go!
Now I look stupid

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It's one of these ones that unless you had ever worked on one, or had looked at a TD5 t-case etc. you would never know. every day is a learning day!

tom1979 said:

I have a discovery NNN ECU too though...

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So to all intents and purposes this is a Disco setup bolted into a Defender - did the t-case come from the same Disco as the ECU?

discomania said:

So to all intents and purposes this is a Disco setup bolted into a Defender - did the t-case come from the same Disco as the ECU?

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No, the ECU was from a different vehicle, and obviously running a Defender map. I will unplug the sensor which should have the same effect as putting it in high ?

tom1979 said:

No, the ECU was from a different vehicle, and obviously running a Defender map. I will unplug the sensor which should have the same effect as putting it in high ?

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I don't know what way it works, i.e. normally open or normally closed, try it and see - won't do any harm.

i read somewhere on here you can bypass the throttle response thingamidigy with the equivalent of a paper clip

windy81 said:

i read somewhere on here you can bypass the throttle response thingamidigy with the equivalent of a paper clip

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Yes, it's just linking out the terminals like I told the OP to do above to test it.

What I'd really like to know is how it defaults when the switch is unplugged completely - from what I can gather online from searching "TD5 fast throttle control" it defaults to high range, and when the earth is made it goes to low. The switch looks like a plunger type so may well be stuck

tom1979 said:

What I'd really like to know is how it defaults when the switch is unplugged completely - from what I can gather online from searching "TD5 fast throttle control" it defaults to high range, and when the earth is made it goes to low. The switch looks like a plunger type so may well be stuck

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Either, make up a basic little test circuit with a tail lamp to test the switch, or if you have a meter disconnect it and meter it out. £7.99 from Screwfix and you will have a little multimeter.