607 4HP20 auto trans temp sensor fault and other issues

[jgra1]

two useful diagnostics there guys

[dieselnutjob]

it has taken me a while to run some wires into the cabin so that i can easily monitor the sensor voltage whist I drive, and today has been the first hot day since then.
On the drive home the transmission temp was varying between about 95 deg C and 105 deg C which I believe is exactly as it should be.
However the transmission didn't go into protection mode today.
The hottest that I saw decelerating after some hard motorway acceleration.
The temp seemed to rise quite quickly and then suddenly went down again as if there's some kind of thermostatic regulation in there.
Now I need to build a proper voltage monitor (as someone suggested) that can log peek value and then wait for the fault to occur so I can see what's what.

[cachaciero]

Think I'm going to buy a MAX1496, some seven segment LEDs and a couple of opamps and knock myself up a dashboard transmission temperature monitor.

Hat fairly and squarely taken off to you on that. Excellent stuff!

I'm working on an allied project to measure gearbox oil pressure. There's a convenient test point in the main gallery from the pump and we're hoping the readings may help indicate when the filter is becoming clogged.

Excuse me if I am telling you something you already know but Lexia and I assume the Pug equivalent will allow you to record parameters while you drive, you can access this parameter and record it for about ten minutes at a time.

Of course this does assume that the ECU is good !

cachaciero

[CitroJim]

On an HP20, you can see temperature on a Lexia but I'm aprticularly interested in the hydraulic pressure inside it... Sadly, the Lexia does not read pressures.

This reminds me. I must go and buy a set of suitable gauges.

[dieselnutjob]

Think I'm going to buy a MAX1496, some seven segment LEDs and a couple of opamps and knock myself up a dashboard transmission temperature monitor.

Hat fairly and squarely taken off to you on that. Excellent stuff!

I'm working on an allied project to measure gearbox oil pressure. There's a convenient test point in the main gallery from the pump and we're hoping the readings may help indicate when the filter is becoming clogged.

Excuse me if I am telling you something you already know but Lexia and I assume the Pug equivalent will allow you to record parameters while you drive, you can access this parameter and record it for about ten minutes at a time.

Of course this does assume that the ECU is good !

cachaciero

Absolutely. I used PP2000 (pug equiv of Lexia) to formulate the voltage vs temp table.
However I don't want to drive around with my laptop on in the car all the time. I do want to monitor temperature at any time and a little discrete LED display will be better for that.

[dieselnutjob]

All through the winter I have not had this fault, and then suddenly it started misbehaving again.
I came off the motorway, did a hill climb and then through the town to my house.
It always seems to freak out after that hill climb.
Anyway when I got home I had a look.
There was a permanent fault logged of the temperature sensor, and it was reading 121 degC in live data.
I cleared the error codes and it didn't come back, despite turning the ignition off and on again etc, which I don't understand. If it's a "permanent" fault rather than intermittent then reseting the codes should not get rid of it, it should come straight back on again.
So now I was looking at an ECU with no error codes saying that the transmission temperature is over 120 degC.
I also plugged my voltmeter into the wires that are still there across the ECU input. 2.36 volts (I think it was) which is consistent with that temperature.
Maybe be transmission really is getting that hot.
Maybe it's getting so hot that the sensor goes "off the scale" and is logged as sensor fault?

So, I need to figure out how the temperature of these transmissions is controlled. Recently my fuel economy has been good and the car drives very well (except when the transmission goes nuts) so I'm hoping that there isn't anything fundamentally wrong. Maybe there is something wrong with the transmission cooler.

[CitroJim]

That's interesting...

The transmission coller is a water-cooled one fed from the top of the engine coolant circuit and returns to the bottom of the rad.

It serves both as a warmer and cooler really as it should keep the gearbox oil at troughtly the btemperature of the engine coolant.

Their water circuit is very similar to the water/oil cooler used on many XU engines and I've known these to air-lock and cause a rise in oil temperature.

The 4HP20 cooler is also very fine and can block if there has ever been any debris in the cooling system (which is why I never recommend any for on rad sealant except FSL on these) so on that basis I'd be inclined to whip the hoses off the cooler and give it a good reverse flush. New coolers by the way are eyewateringly expensive.

The majority of heat in the 'box will be generated in the torque converter when hillclimbing but strictly it should be locked up under such circumstances and therefore not get so hot.

The Xantia ECU contains hot oil maps that come into play at (I think - need to check) 140 degrees. These maps put the 'box into a cooliing regime so for yours to have tripped the over temperature fault it must have got very hot indeed. Did the engine show it was hot too?

[dieselnutjob]

no the engine was showing 90deg on the temp gauge throughout
is it difficult to remove the heat exchanger so that it can be cleaned out off of the car?

[CitroJim]

is it difficult to remove the heat exchanger so that it can be cleaned out off of the car?

It's easy enough. Two big Allen bolts on the cooler allows ot to be lifted off. Undo them equally (very important) as you gently lift the cooler and recover the rubber O rings under them.

[dieselnutjob]

I had an initial look
the hoses that attach to the heat exchanger are well attached (i.e. not coming off without a fight)?
I can see how air might be trapped in there as well as it's a lot higher than the hose from the radiator and not exactly uphill on the other side either, and there are no bleed screws.
For the moment I've chickened out as this looks like a job of a few hours. I need to get my spare car a bit better first I think.

[dieselnutjob]

update
I went to pick up my daughter from school and went with the diagnostics running.
The transmission oil temperature was occasionally jumping up or down 30 deg or so.
In fact as I reversed back onto the drive the temp was 128 degC and suddenly it dropped to 88 degC.
Now I need to monitor the voltage input whilst the temp is jumping about to see if it's the sensor resistance jumping about or if it's something inside the ECU

[CitroJim]

You know, this really sounds like a duff sensor... It's a bit of a devil to swap though as it's a valve block out job and on the Xantia at least, the valve block cover is a bit hemmed in...

A good tip for removing the cooler hoses is to move the wire clips out of the way and then gently 'work' the end of the pipe on the cooler spigots with a pair of waterpump pliers to help break their bond to the alloy. Gentle is the operative word here...

[Franchute13]

Hi.
Sorry for refloating an old thread.
Anyone know how the story ends?

I have the same problem but my 607 V6 is petrol. The box is a 4hp20.
The oil level of the box is correct.
Engine temperature is correct.
The water temperature is correct. The level also.
If the car is driven quietly, no problem.

Thanks

[xantia_v6]

Can you give the specific symptoms that your car has? Also any work or diagnosticd already done to fix your problem. It would help us to give some clear advice.

[Franchute13]

Hi.
Thanks for answering.
Symptoms that appear when the temperature of the gearbox exceeds 110 C.
1) In tiptronic mode would not engage, but with the gear pushed over to the left the dash still said D instead of pushing and pushing it backwards / forwards had no effect.
2) Pulls.

These symptoms disappear when the car is left parked for a few hours. These symptoms never happen if the car is driven slowly. (Speed less than 110km / h)