4HP20 2.2 C5

[cachaciero]

Well I still think it sounds like a sensor fault. I don't think it is likely that an ECU fault is giving the symptoms you are describing.

Does the transmission ECU get its engine load signal direct from the throttle, or via the injection ECU? I suspect that the latter is more likely.

Via the injection ECU I dont think that it looks at throttle position as such rather a demanded torque figure which I think is derived from throttle position and engine revs.

I did take on board your previous comments as regards sensors and seriously revisited the issue,

As far as I can see the ECU only gets three bits of data from the box. input revs, output revs and oil temp and all three sensors are buried in the box, the rest of the data consists of selector and brake inputs (hardware) the rest of the data including dynamic data e.g pitch attitude comes down the CAN bus from the injection ECU and ESP/ASR ECU,

According to the Lexia the outputs from the box are fine and having done several recordings of them they all look sensible to my eye,

But just because the Lexia is being told that that they are good by the ECU and displays data that the ECU gives it doesn't mean to say that there isn't something there which gets filtered out by the ECU,

Given that even when driving the box Tiptronically the ECU still keeps a watchfull eye on the gears selected and will and does overide and change gear if the conditions are potentially damaging, I would imagine that if there were a problem with any of the sensors then this would not work either, in fact thinking about the protection aspect I wonder if there was a problem whether the box would change gear at all probably not except maybe to go to third gear emergency mode.

What I really need is a REAL expert that has the gear to really see what is happening in the ECU, and the breakouts necessary to really examine the signals between the ECU and box.

Having said all of that it has been warm these last few weeks and the other day when in that area I was suprised at just how hot the ECU was after a run, we are talking seriously hot like you didn't want it in your hands for too long. The ECu sits on top of the injection ECU and there is a plastic cover over all that with as far as I can see little possibility of any natural airflow to aid cooling I can't imagine that running at elevated temperatures is good for either the auto box ECU or the injection ECU.

I don't know yet if it is coincidence or not but the last two days the air temp has been considerably cooler and the box has for the most part worked as I would expect it to, so for a while it is a monitor it situation and try to find an autobox specialist that I can have some confidence in.

But any other thoughts or offers of the breakout cables that would allow me to scope the signals from the box to the ECU welcome


cachaciero

[cachaciero]

Well just an update on this problem, appears that I am not the only one with this issue, I have had some correspondence with someone on the Yahoo C5 group who has a similar problem.
For now I have discounted ECU temperature as a cause and come back to "something" external but what?

I have carried out some experiment with driving it through cruise control, not something I use often over the routes I do on a daily basis. The results of this are interesting, when in cruise mode the gearbox performs pretty well much as I would suspect, frequently getting up into fourth once it has achieved commanded speed and eased back on power, this over a speed range of 30 -50 mph, would that the box would do that normally.

According to such info I have the box or rather the ECU uses different maps when in cruise mode and kickdown is inhibited, well not surprising really since kickdown is derived from throttle rate of change calculated in the injection ECU so that fact may have nothing to do with the Box ECU. Thinking that what is the logic here why would the box need different changing laws in cruise?
I really really need details of the maps in the ECU if I knew which map it was following maybe I would get some clue as to what is making it choose that map.

My fear is that we are in an area where everybody can deny any responsibility for knowing anything. ZF get Bosch to produce a control box which has defined inputs and outputs and presumably hard coded defined algorithms for actually controlling the box, the software for vehicle personalization is provided by the car manufacturer. The net result is that each "knows" their own bit and nobody really knows how it all interfaces or works overall so when it goes wrong everybody points the finger at everyone elses bit.

Very frustrating am considering buying a secondhand ECU not because I feel that the one I have is U/S but at least I will have one I can dismantle with a view to seeing if there is anything I can "get at" which may give further clues, but this is all time and money which I would rather not spend.

On the other hand..........Bridgers the local scrapper is not far away.

cachaciero

[addo]

Years ago, I remember a Scandinavian website where the poster was having HDD issues.

Out of frustration, he took the HDD to his local rifle range, and blew some holes right through it. Back home, out of curiosity the deformed piece of kit was plugged in. It still worked somewhat!

Along similar lines, I've been waiting for a post in this thread "Wanted: gearbox ECU without bullet holes"...

You'd think there was enough interest in cracking the code of autobox ECUs, least far enough to get some good data feeds out of them.

[cachaciero]

Years ago, I remember a Scandinavian website where the poster was having HDD issues.

Out of frustration, he took the HDD to his local rifle range, and blew some holes right through it. Back home, out of curiosity the deformed piece of kit was plugged in. It still worked somewhat!

Along similar lines, I've been waiting for a post in this thread "Wanted: gearbox ECU without bullet holes"...

You'd think there was enough interest in cracking the code of autobox ECUs, least far enough to get some good data feeds out of them.

Yes the emotions are getting close to that although with all the other problems the car has I am thinking more like 40mm cannon holes in the whole car

[h2ocooler]

Just a thought, could it be anything to do with the TPS causing the ECU to think there is a higher demand than there really is, Mine occasionally plays up in a very similar way to yours but only very rarely, Im going to replace the MAF at the end of the month due to it being slow off the mark till the turbo kicks in.
When on cruise and it plays up she will loose speed on the motorway sometimes dropping down to 60 from 80 but it will change up to 3rd and rev like crazy, even going into manual and selecting 4th it will then change down to 3rd again within seconds.
Rob

[cachaciero]

Hi Rob

Er......! TPS????
Please clarify

Rgds cachaciero

[The Seasider]

eerrrrrr Throttle Position Sensor ???????????

[cachaciero]

eerrrrrr Throttle Position Sensor ???????????

Ah...! well that's a good suggestion

Lets consider the TPS aka Throttle Position Sensor aka Throttle Pot in relation to the auto box.

The throttle pot data (volts) is read by the injection ECU this appears to use this to calculate several bits of data which it stuffs down the CAN bus to the Auto Box ECU (and the ESP system). These data values are throttle angle, throttle angle rate of change, and demanded torque which is a calculated value one input of which is throttle position (angle)

The autobox appears to use all of these but for what and why is not clear. Traditionally an auto box would use throttle position and road speed as the basic control element and the C5 box may do the same as raw throttle angle is available but demanded torque which is derived from throttle angle is possibly used as the main control input on the 4HP20 as it can easily be compared to actual torque, but then maybe this data is used to control the torque converter lock up rather than the gearchanging, I just don't know.

There are several conditions which will either force the box to hold gears or change down, or use a different MAP, from a driving position it is not easy to work out whether the box is in the right MAP but the gear change is being held back by for instance bend detection or whether it is a completely different MAP as would be the case when "Sport Mode" is selected.

On the AL4 box which uses the same ECU there is a throttle calibration procedure however this does not seem to be required on the 4HP20 where the system appears to be self calibrating. I had reason to adjust the throttle cable just after I purchased the car as there was a lot of slack, according to the Lexia the system seems to have worked out where 0 and max is without any intervention by me.

So in answer to Robs original thought yes in theory TPS might have something to do with it but I can't see how to change anything mechanically that wouldn't change the injection side as well.

To Rob wrt to slugishness at low end i.e less than 2400 rpm have you checked the swirl valve operation, at low revs i.e idle the arm should be full forward, the swirl valve system will fail to valves open and this will make the engine noticeably less lively under about 2200revs just a thought.

cachaciero

[h2ocooler]

Hi Cachaciero
Yes I have checked the swirl valve, its working as it should, even applied vac to it and no leaks from the diaphram, the power kicks in about 1900-2000. I did have a look at the MAF before leaving for France and it was quite green, gave it a blast with carb cleaner and it did seem a bit better on the way here.
When I first got my Lexia I was looking at the real time data and found that my throttle was never going to 100%, only getting to about 87%, I did a bit if poking around and cable was or seemed to me adjusted correctly as the reading went up as soon as I moved it but the range was restricted, I just bent the pedal a bit. on the next drive I did notice that it would now kick down, it very rarely did before. I wondered if the TPS may wear and give inconsistant data to the ECU's.
Rob

[addo]

I have the same incomplete reading from my TPS (exchange rebuilt AL4) - could only get 88%. Measured similar figures on a mates' car. Both went to near or actual zero at rest.

My theory here, is that the transmissions have lost their synching to the actual TPS, and are using a "fallback" reading. PSA talk about programming the pedal to the trans using Lexia, but I'm yet to see an explanation of how this is actually done.

[cachaciero]

I have the same incomplete reading from my TPS (exchange rebuilt AL4) - could only get 88%. Measured similar figures on a mates' car. Both went to near or actual zero at rest.

My theory here, is that the transmissions have lost their synching to the actual TPS, and are using a "fallback" reading. PSA talk about programming the pedal to the trans using Lexia, but I'm yet to see an explanation of how this is actually done.

I need to think about that. For awhile in the back of my mind there has been an unanswered question, why is a pedal calibration required for an AL4 but not apparently for an 4HP20 they use identical ECU's although the code they run will be different. The answer may be that the 4HP20 uses the value of demanded torque from the injection ECU rather than raw throttle angle which the AL4 presumably uses but it is just guess work, sure I have seen a description of setting the AL4 throttle pedal................somewhere

cachaciero

[h2ocooler]

Well just an update.
Drove the 450 miles back yesterday and "some" of the way back it was playing up.
I have noticed that on the motorway sitting at 90 on cruise when it is playing up if I come to a hill or upwards incline the speed will drop, it will stay in 4th until it gets to 70 then it will drop into 3rd, revs go up but it will not go any faster, just sits at 70 with the engine at about 3500-4000, if I select manual and put it into 4th after a few seconds it will drop back to 3rd, flooring the throttle makes NO difference at all, no change in engine sound, no more power etc
To me it now seems like a severe loss of power rather than a gearbox issue, if going through town it will hold onto the gears but still has a distinct lack of power, i will rev but the normal powerband is just not there.
There was no relation to temperature as it will play up and then be alright even without slowing down or stopping.
I have tried unpluging the MAF but all I got was antipollution fault and limp mode, guess I will wait until I replace it and see if there is any change.
Was going to plug the lexia in and go for a drive but dont have a clue as to what parameters I should be looking at.
Rob

[cachaciero]

Well just an update.
Drove the 450 miles back yesterday and "some" of the way back it was playing up.
I have noticed that on the motorway sitting at 90 on cruise when it is playing up if I come to a hill or upwards incline the speed will drop, it will stay in 4th until it gets to 70 then it will drop into 3rd, revs go up but it will not go any faster, just sits at 70 with the engine at about 3500-4000, if I select manual and put it into 4th after a few seconds it will drop back to 3rd, flooring the throttle makes NO difference at all, no change in engine sound, no more power etc
To me it now seems like a severe loss of power rather than a gearbox issue, if going through town it will hold onto the gears but still has a distinct lack of power, i will rev but the normal powerband is just not there.
There was no relation to temperature as it will play up and then be alright even without slowing down or stopping.
I have tried unpluging the MAF but all I got was antipollution fault and limp mode, guess I will wait until I replace it and see if there is any change.
Was going to plug the lexia in and go for a drive but dont have a clue as to what parameters I should be looking at.
Rob

Hi Rob
I agree sounds more like engine than box, might be worth having a look at demanded torque and actual torque although that would probably only confirm what you already know. My first line of attack would be to look at those parameters directly associated with fuel, pressures, third piston activation, intermittent operation of this may cause low fuel pressure etc. I wouldn't suspect the MAF at this stage, seems to me that because of the way they work if it's o.k at 90 for some of the time it is probably o.k the rest of the time.

cachaciero

[cachaciero]

Well as regards my problem have been experimenting further with cruise mode. I now have a new auto driving technique, set the cruise control for min speed i.e about 30mph then use the peddle to drive the car normally. Works a treat as far as checking box performance which selects the gears I would expect under the conditions I would expect in both normal and sport mode. Can be a bit exciting in traffic though cruise is really quite poor at aquiring it's set speed when there are large differences between commanded and actual speed.

The only difference I can see between cruise and non cruise is that the TPS is not used in cruise, is it possible that a noisy pot could keep triggering the kickdown mechanism in the box which may force it to hold a lower gear than normal without material affecting the injection side of things, need to think about that.

cachaciero

[Sid_the_Squid]

Have you tried a more manual solution of changing the box oil? That certainly wears out.