'99 D2 Td5 Auto trans warning lamp - intermittent blink

[Campaspe Man]

I've just joined (finally), and thought I'd kick off with my current annoyance/concern - so thanks for bearing with me whilst I find me feet here.

The short of it is that the auto temp warning lamp blinks occasionally. Hawk Eye shows no auto trans fault codes.

I have tried checking the oil cooler plug, cleaned and refitted and secured it with a tie-wrap so it isn't just flapping around. As I have been towing a bit in the past year or so (and being very nervous about the ability of the 4hp transmission), I have serviced the transmission filter annually. I also swapped the oil cooler with a used one I had (from my donor disco 2) as it had a very small leak -- so I'm unsure whether the changeover could have something to do with the problem...?

I am tempted to think it is an unfortunate gremlin caught somewhere in the wiring... but then I get concerned because the blink only seems to come after the vehicle has been running for a good while, and is climbing. But then it also seems to start when I'm on a bumpy surface - which is difficult because I do a lot of my driving on dirt tracks/gravel roads... which makes me think wiring or connection...

I then feel comforted when I push the vehicle more, and the blink stops - so me thinks that if the transmission was overheating, surely pushing it harder would make the lamp stay on. No? To be clear, the lamp does not stay illumined beyond a second or two, then blinks - sometimes more, sometimes less.

I'd be very grateful for any tests I can run, or tips on understanding the operation of the warning lamp. I have little mechanical training, but have been learning by doing my own servicing/repairs the past 2 or 3 years.

Thanks in advance for any help!

[shack]

It's quite likely that the sensor itself is faulty.

I fitted stand alone temp monitoring for the auto. I'm not even sure what temp the light is meant to come on at on the factory one, but it certainly shouldn't go on and off like that.

[AK83]

My money is on the temp sender in the cooler too. but it could be something else.
You said that you swapped the oil cooler, did you maintain the switch that was in the other cooler, or did you re-use the one in your original cooler?
i.e. unknown temp sender or having removed it and re-fitted could be dodgy.

I had the same issue with my Tdi years back.
I was up in the high country at the time and the trans light came on, panicked like crazy.
But, got under the car and felt both trans and transfer for any excessive heat, and while it was hot, it wasn't scolding hot!

The problem is there are two sensors. One in the auto trans cooler, the other is the transfer box sensor, and they both indicate a trans warning light.

If you're not getting any error codes, then you could disconnect each sensor one at a time and see if it happens again. I don't even know if the ecus (either BCU or ECU) will warn of trans temps).
I would disconnect the transfer sensor and if light comes on, then the auto is the problem.
That's what I had to do, as the Disco 1 doesn't do diagnostics!

The major reason in my case that the sensor was the obvious point to look into was that even when cold, the warning light would come on, before the engine had time to warm up.

IIRC, the sensor light comes on when trans or transfer reaches something like 115?C, so it will be very obvious if your mechanicals are not blistering hot, but warning light comes on.

[Campaspe Man]

Thank you very much Shack and Arthur.

I have been thinking about the sensor too, so good to hear your thoughts about this. I didn't use the sensor from my previous cooler - I obviously haven't looked closely enough as I'd assumed it wasn't possible to switch out the sensor from the cooler (I'll have another look at that).

No, I don't believe anything was blistering hot, but I'm thinking to see what sort of temperature reading I can get on the transmission oil pan now that I have Arthur's indication of 115 degC. (I don't know if this is off-track, but the Hawk Eye transmission menu includes an "Engine Temp" live reading - which confuses me as to why this is in the trans menu - could it be the transmission oil temp? Anyway, that reading was showing as being 93 - 96 deg C when I checked it whilst getting the blinking warning lamp).

Arthur, am I right in understanding you as saying a sender in the Transfer box and the trans oil cooler both connect to the warning lamp? I'll go over your description again, and give that a go.

Thanks very much again.

Myles

PS how do you create your signatures for your messages, please? Haven't worked that out yet.

[shack]

(I don't know if this is off-track, but the Hawk Eye transmission menu includes an "Engine Temp" live reading - which confuses me as to why this is in the trans menu - could it be the transmission oil temp? Anyway, that reading was showing as being 93 - 96 deg C when I checked it whilst getting the blinking warning lamp).


That will be the engine coolant temperature that is passed to the TCU via the canbus, it's used along with a software timer to prevent the auto from locking up until it is warm enough.

Nanocom reports it as well but the temp is completely wrong.

[AK83]

......

Arthur, am I right in understanding you as saying a sender in the Transfer box and the trans oil cooler both connect to the warning lamp? I'll go over your description again, and give that a go.

Thanks very much again.

Myles

PS how do you create your signatures for your messages, please? Haven't worked that out yet.

1st point: yes. there is the sensor you already know about in the trans cooler.
There is also a sensor on the passengers side of the transfer box.
According to RAVE they're both using a black/light green wire. Both these wires end up at a 20pin orange connector on the RHS under the drivers side under dash recess.
From there, one of those Black/light green wires goes to the warning light.

Do you have a copy of RAVE?

2nd point: up at the very top RHS of the webpage you see My Profile and Settings. Hit Settings, and on the LHS column of that page under My Settings you will see the link to edit your sig.

[shack]

There is also a sensor on the passengers side of the transfer box.
According to RAVE they're both using a black/light green wire. Both these wires end up at a 20pin orange connector on the RHS under the drivers side under dash recess.
From there, one of those Black/light green wires goes to the warning light.


Quite a number of vehicles don't actually have the sensor (or the wiring) in the transfer case, in fact I've only seen 1 myself, so I'm not sure how many actually have them.

That's my knowledge on it anyway, I could be wrong and I just own a couple of unicorns..

[Campaspe Man]

Thanks Arthur and Shack.

I'll work on this today and let you know what I find -- including whether I have a sensor on my Transfer Case!

No, I don't have Rave even though I see it mentioned all the time. I think when I last tried to obtain it, the available link didn't work. Any suggestion how best to obtain it?
I do have the 3 volume LR workshop manual for D2 - a blessing and a curse.

As for Signatures, it seems that I don't yet have that option - perhaps I need to prove myself a bit more first?

Cheers, and I'm very grateful for all the help. Next up from me will be an SRS fault that has just come up...
Myles

[Campaspe Man]

Quite a number of vehicles don't actually have the sensor (or the wiring) in the transfer case, in fact I've only seen 1 myself, so I'm not sure how many actually have them.

That's my knowledge on it anyway, I could be wrong and I just own a couple of unicorns..

Just to confirm that neither my 99 nor 2004 Transfer Box's have the temp sensor -- although I see that the LR workshop manual at 41-4 indicates an "Oil temp switch - if fitted" at the location suggested by Arthur.

I've decided to swap the oil cooler temp sensors (hopefully without causing too much damage), and see whether the blink disappears.

On a test drive today I struggled to get the blinking warning lamp more than once, and when I surveyed the temperatures of the auto/engine/etc using a laser thingy, nothing seemed out of the ordinary (even allowing for some discrepancies).

[Graeme]

Moisture and dirt can get into the electrical connector for the unfitted transfer case sensor causing an over temperature indication. The connector will be tucked-up out of the way.
IIRC the sensor was only fitted to V8 autos but I fitted one to my TD5 manual.

[shack]

IIRC the sensor was only fitted to V8 autos but I fitted one to my TD5 manual.

Good call, the one I've got with a sensor in it is from a V8 auto. Interestingly the loom in D2a TD5 didn't have the wiring from memory.

I tried to replace a faulty loom in the D2a and it was somewhat different to the earlier V8 I wanted to use.

[Graeme]

It may have been my 99 to which I fitted the switch. On my 03 D2a manual TD5 I connected my engine temperature alarm to the auto temperature sensor circuit. I have recollections of having to find the unused socket at the radiator, although that may have been my manual 84 RRC which told me after a river crossing that the auto's oil was too hot.

[Campaspe Man]

So, I followed up on the advice in relation to the unused sensor wiring at the Transfer box that hooks into the auto trans oil temp warning light... (with thanks to Arthur and Graeme).

Frankly, I wasn't expecting much to come of this, but thought it made sense to follow Graeme's advice that dirt build up in the unused plug/s can lead to an incorrect warning, and so I pulled them down from on top of the box and gave them a good clean, and even put some electrical tap on to close them up.

That was yesterday. Today I decided to a proper test, so I connected my tandem trailer and collected a load of bricks about 25 mins from home. The return trip with bricks included extended hill climbs... and, I have to say, no blink at all in warning lamp! This is the first drive (with or without trailer) that I didn't get a blink in a couple of months. So fingers crossed.

Oh, and as soon as I got home, I pointed the laser temperature gun at the auto box, and the highest reading I could get was just under 90 deg C (on the upper part of the casing).

Thanks again for all the help, and hopefully this one is ticked off.

Myles