Violent gear changes C8 Auto

[jscadden]

For approximately the first mile after starting in the morning, I get violent gear changes. Seems to be worse on colder days. Normally no trouble for the rest of the day unless it doesn't get used again till the evening. Acceleration is a bit sluggish till it's warmed up. Once or twice, the gearbox warming has flashed up.

The gearbox was replaced August last year! The CV joint collapsed and was replaced but made no difference to the problem.

Gearbox levels were checked by a mechanic so should be OK!

[GiveMeABreak]

Do you have access to Diagbox / Lexia? If you have an error there will be a code or 2 logged in the ECU. We really need those to help with he fault diagnosis.

Also, when the gearbox was replaced, did they reset the oil counter?

[jscadden]

I've put my OBII reader on it and no codes were displayed even when the error showed up briefly.

The company who replaced the gearbox and Torque Convertor were reasonably big although not a national chain (Dashcam caught a few moments) but I have no way of knowing for certain if the oil counter was reset. They are situated at the opposite end on the M25 to me so it's not viable to pop in for a check.

John

[GiveMeABreak]

Don’t forget generic readers won’t be able to read all the ECUs. They do have problems reading dome ECUs. If there was an error flagged as a gearbox fault on the dash, then there will be a logged fault code.

[jscadden]

Took the car to a Bosch Service Centre where they connected up. A few error codes were displayed but nothing that appears to be gearbox related.

The codes were: P1442, P1435, P1537, P0115, P0401, P0246, P0380.

He did find that the Intercooler pipe was split which resulted in a loss of power and you may recall that I had problems with a faulty coolant temperature sensor connector.

He agreed that there were violent gearchanges when cold but could not find the cause.

John

[GiveMeABreak]

Ok, so I think you need to take a step back and not get too focused on the gearbox for a second:-

Although none of these codes are generated by the AL4 gearbox ECU, they are generated form the Engine Management ECU. Any issues with the air, fuelling or emissions system will impact on the engine performance and as a consequence on the drive-ability of the vehicle.

If you had a manual gearbox, these symptoms would probably appear to be like a sudden loss of power or juddering / jerking for example - but because you have an auto box, it is more prominent and natural to assume it is gearbox related.

Let's ignore the P0380 code at present as that is just primarily for pre-heating and for DPF regeneration assistance (when needed).

However, you obvioulsly have issues with both the EGR and Turbo air circuits that could be causing those errors and on top of that, you have additive system faults and one associated with the accelerator.

Any or all of these can affect the engine ECU, and that may result in the vehicle going into a backup mode which will result in restricted engine power - but can also cause stuttering and lack of power.

As a result, the AL4 Auto box may well be affected as if it comes to change a gear and there is a power loss because of the engine faults, then it may try to revert back to the previous gear and this may cause the jerking or rougher gear changes. On a manual, as the car would be put into gear manually or whilst in gear it would be interpreted as hesitation or loss of power when changing up. While this is happening, things such as cruise control will not work (although I appreciate you don't have this fitted on your C8).

P1442 Additive quantity fault
P1435 Fuel additive system fault
P1537 Fault: accelerator pedal jammed
P0115 Engine coolant temperature signal fault
P0401 EGR air circuit fault
P0246 Turbocharger pressure fault
P0380 Fault on the pre-postheating relay circuit


So I would for now, focus on getting these other issues eliminated.

Have you had any warnings about the particle filter being blocked or to top up the additive tank? If not, when was it last topped up and what is the current mileage?

I would then start getting the EGR and Turbo solenoids checked and makes sure these are operating and work from there.

[jscadden]

The engine coolant temperature sensor was replaced back in June 2019 and still produced a problem which was dealt with on another post. Turned out to be a bad connection.

The Diesel additive level warning has flashed up on a couple of occasions. I have no idea when it was last topped up! The current mileage is just under 186K.

The engine management light has started coming on but no associated warnings.

John

[GiveMeABreak]

Ok, so that is well past the top up point - and I would suspect that it has been topped up already at some point - but may be due for another top up.

The Additive system on your C8 is of the older type and has a separate Additive ECU. On newer vehicles, this function is managed by the Engine ECU directly. In the early days - these ECUs were notorious for refusing to be reset by the diagnostic equipment after the additive level was topped up. Consequently they were constantly throwing up errors. The know solution was to replace the additive ECU. It's a Marwal unit.

Part no: 1525CZ for reference.

Item 40 on the diagram:

So that may be one reason why you are getting warnings - either the ECU has not been reset and thinks there is insufficient additive in the tank (it is not physically measured with a gauge - only estimated from the top up and reset against the mileage and fuel added).

[jscadden]

Had all work done as suggested and additive topped up and reset etc.

Not much difference, although there is more power, but got my mechanic to reproduce the problem. His thoughts are that there is probably some sludge in the gearbox which is causing a slow take-up of fluid till the fluid is warm allowing it to circulate better. The problem only occurs when the gearbox is cold, i.e. first thing in the morning for the first mile. After that, gear changes are perfectly smooth.

His solution is to remove the sump plate on the gearbox and clear out any sludge etc.

As he is not specifically au fait with the C8, he would appreciate any comments.

John

[xantia_v6]

From reading this old topic viewtopic.php?t=35439 , one gets the impression that rough changes are not unusual with the AL4.

I have read that harsh shifts when cold are a symptom of the fluid level being too low, causing the pump to be picking up air with the fluid. When the transmission warms up, the fluid expands and air is no longer pumped.

[white exec]

Correct fluid, as well as level?

[wheeler]

And does your mechanic know how to check the gearbox oil level correctly? Its a very specific procedure. The oil has to be at the correct temperature (60 degrees from memory), you then need to add half a litre of oil & remove the level plug with the engine running.
They would have needed a diagnostic running reading live data of the gearbox oil temp sensor.

[jscadden]

I'm going for a fluid top-up which I believe requires a specific procedure! Have you got a link to it? I did print out one but it seems to have got mislaid!

John