Some examples of the Ford Mondeo suffer from faults in the control module of the electric tow bar, causing the tow bar not to deploy or to get stuck halfway. Although this is a rare problem, it can be quite frustrating when you suddenly need to hook up a caravan or trailer. Fortunately, the fault is often covered under warranty. A targeted diagnosis is the first step towards a solution.
How does an electric tow bar work?
An electric tow bar is not a simple mechanical flip-out construction. The system consists of an electric motor that folds the tow bar in and out, controlled by a control module. That module receives signals from various sensors and switches, such as position sensors that register the start and end positions, locking sensors that check whether the tow bar has clicked into place correctly, and current sensors that monitor the motor’s power consumption.
As soon as you deploy the tow bar using a button in the boot or on the dashboard, the module controls the motor until the tow bar reaches the correct end position. If any signals deviate, the module switches off the motor to prevent damage. This safety mechanism prevents the motor from burning out or the mechanism from seizing. Diagnosis is sometimes tricky. It is not always clear whether the problem is mechanical, electrical or in the software.
What exactly does the control module do?
The control module is the electronic brain behind the electric tow bar. This module processes information from various sensors and then controls the electric motor based on that data. Specifically, the module monitors:
- Position feedback to know where the tow bar is located
- Locking status to be sure that the tow bar is correctly secured
- Current consumption of the motor to detect overload
- Communication with other modules in the vehicle
If one of these signals is missing or deviates, the module switches off the motor as a safety measure. As a result, the tow bar can no longer move or gets stuck halfway. The system also communicates with the body control module and sends fault messages to the dashboard, so that you as the driver know that something is wrong.
How do I know if my control module is faulty?
A faulty control module gives off signals in several ways. The most common symptoms are clear and easy to recognise.
The tow bar does not respond or stops halfway
This is the most classic symptom. You press the button to deploy the tow bar, but nothing happens or the tow bar gets stuck halfway. Sometimes you can hear the motor trying to run, but it stops prematurely. This may indicate a problem with the position sensors, causing the module to no longer recognise the end position.
Warning messages on the dashboard
Many cars display a message on the dashboard when the tow bar is not correctly locked or when the system detects a fault. These messages can range from a simple warning light to a text message stating that the deploy function is not available. Sometimes this is accompanied by repeated beeps.
Intermittent faults
The tow bar works one time and not the next. This kind of unpredictable behaviour often points to moisture in the connections, a bad earth or corrosion in the wiring. It can also indicate a module that occasionally fails due to temperature fluctuations or vibrations.
What are the most common causes?
A faulty control module is rarely an isolated problem. There is often more going on than just the module itself.
Moisture and water damage
Moisture is one of the best-known enemies of electric tow bars. Water finds its way in via the tailgate, wiring in the boot or connectors under the car. Once moisture reaches the module housing or plugs, corrosion develops and signals start to go wrong. This leads to failure of the electronics.
Mechanical resistance or faulty motor
If the mechanism is stiff due to dirt, rust or wear, the motor current increases. The module detects this overload and switches off the motor to prevent damage. To the driver, this feels like a module fault, while the real cause is mechanical.
Incorrect calibration
On certain systems, the tow bar must learn its end positions during a teach-in procedure. If this calibration (setting the start and end positions) is lost due to a battery disconnection or has never been completed properly, the module no longer recognises the positions. The tow bar may then stop prematurely or fail to lock.
Sensor and cable faults
Micro switches, Hall sensors and position sensors can fail due to wear, vibrations or moisture. Cables are also damaged by movement and weather conditions. Loose or corroded connectors likewise lead to incorrect signals.
Internal faults in the module
The module itself can develop internal faults due to ageing, voltage spikes or failing electronic components. In that case, repair is sometimes possible. Often, the complete module is replaced.
‘ A poor earth often causes strange faults that appear intermittently (for example, only at certain temperatures or after use). ’
How should you approach the diagnosis?
A targeted diagnosis prevents unnecessary repair costs. Always start by reading out fault codes from the relevant modules. The tow bar module itself provides information about the problem, but the body and comfort modules also provide valuable clues. Sometimes there are no direct fault codes in the tow bar module, while other modules do provide a hint.
Then carry out a visual inspection. Check plugs, wiring, corrosion, signs of moisture and mechanical damage. Move the tow bar manually to feel whether it moves freely or is stiff. Also check the voltage supply and earth. A poor earth often causes strange faults that appear intermittently (for example, only at certain temperatures or after use).
If the mechanism is stiff, first clean it and lubricate where permitted. A motor or module can switch itself off if the resistance becomes too high. With many electric tow bars you need to carry out a new adjustment or reset. This means that you let the tow bar learn its start and end positions again. If the end points have been lost, the tow bar will sometimes work normally again after a successful teach-in procedure.
If the problem persists and the wiring, mechanism and sensors are in order, the module remains as the suspect and testing or replacing it is the logical next step.
How expensive is replacement of the control module?
The cost of a new or refurbished control module varies greatly by make and model. For the Ford Mondeo, the price of a new module is often between 300 and 600 euros, excluding labour. At a dealer you will usually pay more than at a specialist garage.
Specialist companies repair some modules. This often costs between 150 and 300 euros and is an attractive alternative if the module is not yet completely defective. Do bear in mind that repair is not always possible, especially not in cases of water damage or internal short circuits.
If the problem is covered by warranty, you can often have the repair carried out free of charge at the dealer. Always check first whether you still have warranty before you start working on it yourself or call in an external party.
Practical tips for maintenance and preventing problems
Regular use of the electric tow bar prevents the mechanism and motor from seizing. Even if you do not use a trailer, fold the tow bar in and out from time to time to keep the moving parts operating smoothly.
Keep the area around the tow bar free of mud, salt and dirt. After wintry conditions, it is best to check for corrosion or seized parts. Have any moisture in the boot or around the rear light area dealt with immediately, as this can seep through to the module.
Only lubricate where the manufacturer allows it. Using the wrong lubricant can actually attract dirt and cause additional resistance. Make a note of exactly when faults occur, such as in cold weather, after washing or after longer periods of standing still. This information helps with diagnosis.
‘ Some systems respond with repeated warnings as soon as a component is missing, which makes further diagnosis more difficult. ’
When should you see a specialist?
Go to a specialist if the tow bar gets stuck halfway, the motor makes a noise but nothing moves, there seems to be water in the module, fault codes keep coming back or the teach-in procedure fails. A specialist garage or dealer has the right diagnostic equipment and knowledge to locate the problem quickly.
Do not try to disconnect components yourself without knowing whether the car will continue to display a fault message. Some systems respond with repeated warnings as soon as a component is missing, which makes further diagnosis more difficult.
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Frequently asked questions
You can recognise a potentially faulty control module from a tow bar that does not fold in or out fully, gets stuck or will not lock. Warning or fault messages often appear on the dashboard and/or you hear beeping or warning signals. The operation may also be intermittent: the tow bar works one time and not the next, for example after rain or washing (moisture/corrosion). If the mechanism and power supply appear to be in order but these symptoms persist, the module itself is suspect.
The most common causes of a faulty control module for an electric tow bar are moisture or water damage to the module and connectors, and cable or plug problems (corrosion, broken cables, poor earth). In addition, a faulty electric motor or excessive mechanical resistance often leads to overcurrent, causing the module to switch off as a safety measure. Faulty sensors (position or locking sensors) and incorrect or lost calibration of the end positions also cause many faults. Finally, the module itself can fail internally due to ageing, voltage spikes or electronic component failures.
In theory, you can replace the control module yourself, but because diagnosis, teach-in/calibration and integration with other vehicle modules are required, it is strongly recommended that this is carried out by a specialist. Repairing the circuit board yourself is usually not worthwhile unless you are very experienced with automotive electronics. As a rough guide, expect to pay around €300–€700 at an independent specialist or tow bar specialist for diagnosis, (dis)assembly, teach-in and a new or refurbished module. If only moisture or plug problems are resolved and the module itself is still good, the costs may be limited to around €100–€250.
Use the tow bar regularly and keep the mechanism, pivot points and the area around the tow bar clean from dirt, mud and salt, only lubricating where the manufacturer permits this. Periodically check the cables, plugs and earth connections in the boot/rear bumper for damage, corrosion and signs of moisture and have any leaks repaired immediately. During servicing or after a fault, have the end positions/teach-in procedure run again where necessary so that the module correctly recognises the positions. If you have repeated fault messages or are in doubt, go to a specialist in good time to prevent overloading of the motor, sensors or the module itself.
With a faulty control module, the tow bar may unexpectedly fail to deploy, get stuck halfway or not lock correctly, which is unsafe when towing a trailer. The system may continue to issue fault and warning messages and switch itself off as a safety measure. There is a risk of further damage to the motor, mechanism or electronics due to incorrect loads or repeated incorrect movements. In addition, from an RDW perspective, the car may be regarded as incorrectly equipped if an unreliable towing device is present.