Alko ATC jammed / stuck on ... evidently not a 'fail safe' system

Aug 15, 2017
A general Google reveals what I mention below to not be uncommon but it searching ATC / ATC stuck and similar variations on this forum yields little, the most promising at first glance being something from 2008 which I chose not to reply to.

Basically, we noticed when taking the caravan to be serviced that the ATC light didn't come on nor did it do its usual whirring kerclunk self test. Never mind. Took it to be serviced. Eventually collected it, what with the Boris Bug and all, late last year and it still didn't seem to work. Dealer connected their workshop 12V supply and it worked. Back on the car, nothing. The dealer warned that it must be the car and that if there was an intermittent connection or some other related fault in the car's socket then its quite likely the ATC unit could start its self test procedure, put the brakes on, then lose power before releasing the brakes. ie. you could end up with the caravan's brakes jammed on. I thought it unlikely as the apparent fault had existed without apparent bad side effect for probably the last two or three times we'd towed it, and I drove for about 40 minutes down the A1. Got home ... wheels/brake drums quite a lot warmer than usual. Drove it next day 15 minutes to our storage site, wheels/brake drums very very hot!! Looked underneath and could see the rod that comes in and out of the ATC unit depending whether brakes on / off had, just as the dealer forewarned moved to the brakes on position then stopped. I rigged up a spare 12V battery to the caravan's trailer plug and watched the rod retract to its normal position once powered on. So the dealer was right. Google reveals this is not at all uncommon. Seems highly dangerous to me that the system is not fail safe and reverts to brakes off in the event of no power. Anyone know if this is some kind of glitch in a particular era or model number of somesuch of ATC units? I've taken the car to a supposed trailer electrics specialist who reckoned there wasn't anything wrong the car. What's other's experiences of this? Is there a fix ... besides have done with ATC and remove the appropriate fuse from the car to disable it completely? Anyone ever found much real detail or point of contact for ALKO? I see Google would have you believe they're a lawn mower manufacturer, persevering you get as far as seeing they make trailer chassis, but any deeper or technical than that is hard.
Mar 14, 2005
First of all if you have a safety concern, then I think you should be first contacting your supplier or the manufacture of the device and raise it with them.

Basically becasue you are not required to have ATC or other similar systems fitted to towed trailers, they cannot be taken or assumed to be part of an essential safety system, and they should not be treated as such. In essence you should load and use a trailer as if it only has the normal braking system, and consider the likes of ATC in the same way that you would consider seatbelts, they are there in case of a momentary lapse of control, they should not be used to bring a wayward trailer under control so it can be towed. Given that perspective, it is perfectly normal and reasonable for such a device to revert to being inactive in the event of a loss of power.

Wikipedia is not a reliable source for all information.

Check out the manufacturers web site on

Aug 15, 2017
Thanks for the link.

Yes, you would have thought it would be reasonable for such a device to revert to being inactive in the event of a loss of power, not potentially get stuck in the 'on' position! I see they in fact have premises in Coventry, so will be seeking their thoughts!


Mar 14, 2005
I suspect that the premises in Coventry may only be a service centre.
The main Al-KO premises is in Southam, Warwickshire and that is where your questions should be directed.
Nov 16, 2015
I have had the AlKo System on my last two caravans, and at times have had spurious connections , which have required , disconnections and reconnections, or with a flashing green , a gentle pull forward and a reverse to get a steady green light. I have done the same with a red light. As yet never had a solid red light stay on and have to , " do the job underneath" if I get a red light I will have to read the destructions .

AlKo at Southam are very nice to talk to. A great bunch of folk.
Jun 16, 2020
I sympathise with the OP. I once had an outfit with awkwardly positioned 7 pin sockets. Unplugging was not always quick. And on a few occasions it accidently reconnected causing the self test system to start. I then would find the brakes fully applied when I came to manoeuvre the van. Having realised the issue, I fitted a 13 pin plug. And made sure on that, and subsequent cars. That the power supply lead is oversized and well installed. Any hint of intermittent supply can lead to the brakes being applied while in motion. Don’t fancy that happening.

On some vehicles, I believe the permanent power supply is of a lesser gauge than that recommended by Alko.

Oct 8, 2006
For a start, if the caravan or ATC is still under warranty the OP should be hammering the dealer, not contacting Al-Ko. Having said that in the few contacts I have had with Al-Ko I have always found them very helpful.

To me this sounds like a power problem on the vehicle - I didn't read in the above anything about whether the vehicle (or caravan for that matter) had been used with ATC before or if this is/was new. Assuming a 13 pin connection, the OP needs to make sure that 12V is present all the time on pins 9 (+ve) and 13 (-ve) - it is just possible that it may have been wired through a smart relay so that 12V is only present when the car engine is running or at least when the ignition is switched on. If it has been so wired it is WRONG and needs fixing. Was the LED checked for operation when the ignition was switched on or when the engine was running - might give some pointers? (The socket pin numbers/positions are embossed on the inside of the socket cap.)

It is also possible that there could be a fault in the supply wiring which means that the ATC is not getting the full 12V which is why it might have moved to brakes part or fully on but does not retract as the electronics is still sensing some supply volts. AFAIAA the ATC should/will default to a safe state, i.e. brakes off, which is why the system cycles when power is first applied.

Finally a thought: this could be an earthing issue. It would be well worth taking some time to check earth continuity around both the car socket and the caravan plug, for instance making sure the earth on the car (pins 11 for fridge and 13 for supply) is to a substantial body earthing point that has had the paint cleaned off to bare metal before attachment and (IME at least) I would lather some Waxoyl on the earthing point once it is tight to ensure there is no corrosion. If the worst comes to the worst a pair of jumper cables connected in series could be used to take earth direct from the battery negative to the socket earthing point and see what effect it has on the ATC cycling?


May 7, 2005
Another potential aspect that needs checking is the car's fuse to the maintained 12 V positive pin.
The current rating with this pin also powering the ATC can be higher than some vehicle makers provide, Land Rover having been a case. They permitted the dealer to upgrade the fuse, specifically because I had the ATC and with it might see high "spikes" greater than the car's wiring system was conceived to take.
If this fuse blows whilst the ATC is drawing power the brakes can be left on almost anywhere; clearly if it is going to blow then whilst the ATC is moving its actuator is when it is likely to happen.
From memory, the factory fitted fuse was 15 Amps, the dealer refitted a 20 Amp fuse. I have never blown a fuse, but never used a 15Amp one either knowing the issue from Al-Ko's data, and thus asked the dealer to sort out things with LR's technical people.

As the OP had the service people function the ATC, it should at least for the run home have freed the brakes. If it was dragging, or anything up to the 40% max applied the system can do, then the brakes will be stinking hot after quite a short run.


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