Cintroen c3 al4 2003

[Kakjim23]

I have a 2003 Citroën C3 1.4 with an AL4 automatic transmission.

The transmission intermittently starts slipping, and the Sport and Snowflake warning lights come on. After turning the engine off and restarting it, the transmission can sometimes work completely normally again. There are also times when I can drive for about an hour without experiencing any problem at all.

A diagnostic scan reportedly showed “slipping clutch/brake.” However, the mechanic who performed the scan only spent about 5 minutes checking the car and did not inspect the transmission fluid, hydraulic pressure, solenoids, or valve body.

He told me that the transmission definitely needs a complete rebuild, costing around €3,000.

My question is: can a complete transmission rebuild really be diagnosed with certainty from a diagnostic scan alone? Could the same symptoms be caused by pressure problems, pressure-regulating solenoids, the valve body, or another issue that could potentially be repaired for significantly less?

I would especially appreciate an answer from someone with actual experience working on AL4/DP0 transmissions.

What tests would you recommend performing before concluding that a complete rebuild is necessary?

[mickthemaverick]

How many miles has the car done and has the transmission fluid ever been changed?

[ozvtr]

The transmission intermittently starts slipping, and the Sport and Snowflake warning lights come on. After turning the engine off and restarting it, the transmission can sometimes work completely normally again. There are also times when I can drive for about an hour without experiencing any problem at all.

Sounds like the main pressure regulator solenoid if the gearbox works fine after shutting the engine own and restarting.

A diagnostic scan reportedly showed “slipping clutch/brake.”

There are three clutch packs and two brake bands. Which one is slipping? Its a rhetorical question.

Could the same symptoms be caused by pressure problems, pressure-regulating solenoids, the valve body, or another issue that could potentially be repaired for significantly less?

The main pressure regulator is cheap and relatively easy to replace. It's the cause of a lot of AL4 failures. I would replace that and definitely change the fluid.

What tests would you recommend performing before concluding that a complete rebuild is necessary?

The AL4 is very compact and you need to literally pull the gearbox apart to get to anything! So while you are in there you would change the friction plates, seals and bands.
Another failure mode is that the brake band friction material can wear down and expose a rivet on the band causing the rivet to ride on the planetary gear drum instead of locking the drum. This also damages the drum!

[Kakjim23]

Do you think it would be worth replacing the pressure control solenoids and the gearbox oil first, before considering a gearbox replacement or rebuild?

I'm asking because every garage I've visited so far has recommended replacing or rebuilding the entire gearbox, without giving me a more specific diagnosis. Since the fault temporarily disappears when I turn the engine off and restart it, do you think I should try replacing the solenoids and the oil first, or is there a serious possibility of internal mechanical wear? the car has 100000

[ozvtr]

You need to find an auto transmission specialist. I'm not sure a regular garage could do it. Maybe, but most don't go into the "guts" of the transmissions.
If it was me, I would give it a try. It wouldn't take a specialist long to change the fluid and the solenoids.
If you get it done tell them to only use a synthetic fluid and add Lucas transmission fix.

You could try the synthetic fluid and Lucas transmission fix first, if you want, it's not hard to do. The cost of the fluid and the transmission fix is about £50. So it's worth a try.
If you are not getting a "pressure regulation fault" it might not be the main pressure regulator solenoid.
Can you hear the solenoid buzzing (from outside the car) when you put the gearbox in reverse or drive? Start the car and just open the drivers door and listen for the buzzing from under the car. Move the selector between N and D and listen. If you can hear buzzing the solenoid might not be faulty.

[Kakjim23]

I took the car to an automatic transmission specialist. They inspected it and told me that the gearbox oil was in very poor condition. As far as we know, it may never have been changed before.
They also found an issue with the hydraulic pressure and believe that the old oil could be contributing to the problem.
They recommended changing the gearbox oil first (€270) and then checking how the transmission behaves. They haven't checked or replaced the solenoids yet. They said that if the problem persists after the oil change, they will investigate the pressure solenoids further.
One thing worth mentioning is that the car drives normally most of the time. The Sport and Snowflake warning lights appear intermittently, and restarting the engine usually makes them disappear temporarily.
They also mentioned that the clutch packs/friction discs could potentially have suffered wear due to the old oil, but checking their condition would require opening the gearbox.
What do you think? Do you believe there is a good chance that changing the oil will solve the pressure issue, or should I expect the pressure solenoids to need replacing as well?

[ozvtr]

What do you think? Do you believe there is a good chance that changing the oil will solve the pressure issue, or should I expect the pressure solenoids to need replacing as well?

See my previous post. Did you try listening for the buzzing solenoid?

On the surface it sounds like they know what they are doing. Changing the oil is a good start. At least they didn't go in headfirst and say you need a rebuild! Never make assumptions. Look at the symptoms. See if any known failures fit the profile. Old fluid is a known failure point. Always start with the quick, cheap and easy fixes...there is far less to lose if it's wrong.
I have just found out, personally, that the fluid is critical to the operation of the gearbox! Even brand-new fluid of the wrong type will cause gearbox problems, so old fluid will not help.
As I said, you are not getting a pressure DTCs (Diagnostic Trouble Codes), so at least the gearbox doesn't think there is a problem with that.

[ozvtr]

One thing worth mentioning is that the car drives normally most of the time. The Sport and Snowflake warning lights appear intermittently, and restarting the engine usually makes them disappear temporarily.

You do have a "slipping clutch" DTC. Every time a clutch slips, even for a moment, the gearbox ECU may "down grade" the gearbox action. That is; flash the * and S symbols and lock the gearbox in third. When you turn the ignition off, it resets the ECU. The car will usually drive fine until a clutch (or something else) fails, again, and the ECU downgrades the gearbox again. The gearbox ECU will not downgrade the gearbox for every failure, just some. And the failure only needs to happen for a moment, and then go back to normal, but the ECU will log the fault and downgrade the gearbox until reset again. Despite the fact that the fault might have only been temporary.