The 2.7 HDi V6 in the Citroën C6 can refuse to start due to problems with fuel pressure, electronics or the preheating system. What often begins as slow starting in cold weather sometimes develops into complete failure. These starting problems are often caused by a combination of small faults. Diesel technology is sensitive to this. Discover which causes are behind the starting problems and what you can do about them.
With the Citroën C6 with the 2.7 HDi engine, owners regularly report complaints about difficult starting. Sometimes the engine does turn over on the starter motor, but does not fire. In other cases, starting takes unacceptably long, especially at low temperatures.
These starting problems are rarely caused by a single issue. It is usually a combination of factors. The 2.7 HDi is sensitive to voltage drop, blockages in the fuel circuit and faults in sensors or pumps. The C6 is a complex vehicle with a lot of electronics. Small deviations therefore already have major consequences for starting behaviour.
Common causes of failure to start
Most starting problems with the 2.7 HDi engine fall into several categories. Each of these causes on its own can already lead to starting problems. They often reinforce each other.
Battery and voltage problems
The Citroën C6 is particularly sensitive to low on-board voltage. A weakened battery leads to slow cranking, but also to error messages in the electronics and engine management. This can prevent the engine from starting at all, even if the battery still seems strong enough to turn the engine over.
Owners who use the car infrequently experience this problem more often. The C6 has high power consumption when parked because of all its electronics and comfort systems. A battery that is not regularly recharged quickly becomes exhausted.
Fuel pressure and pump problems
Insufficient fuel pressure is a very common cause of starting problems in diesel engines. In the 2.7 HDi this can have various causes:
- Blockage of the fuel filter due to contamination or water
- Air leaks in the supply line between tank and pump
- Wear of the lift pump that provides the feed pressure
- Problems with the high-pressure pump that pumps the diesel at high pressure into the rail
- Pressure loss in the common rail due to leakage or sensor defects
In real-world cases, the high-pressure pump is explicitly mentioned as a cause of persistent starting problems. If this pump does not build up the correct pressure, the engine does not receive enough fuel to be able to start.
Glow plugs and preheating
For cold starts the glow system is essential. Diesel engines need preheating in order to start at low temperatures. One or more glow plugs may be defective, or the control of the glow system may not be working properly. In that case the engine starts poorly or not at all in cold weather.
This problem is easy to recognise: the car often starts well when warm, but when cold it takes much longer or fails altogether. At temperatures below zero a defective glow system can completely prevent the engine from firing.
Sensors and engine management
The 2.7 HDi engine uses various sensors to control injection and timing. Faults in these sensors can lead to incorrect engine behaviour and starting problems. The ECU then receives incorrect information about pressure, temperature or position. On that basis the ECU decides to block the engine or limit the fuel supply.
This is often accompanied by an engine warning light on the dashboard. Fault codes in the engine management usually point towards the cause, but without diagnostic equipment you are left guessing.
‘ This requires specialist diagnosis and repair, because the high-pressure system operates under extreme pressure and is not suitable for DIY repairs. ’
Diagnosis of starting problems with the 2.7 HDi
A systematic approach is needed to find the real cause of starting problems. Start with the most common and easiest causes to check. From there, work your way towards the more complex systems.
Initial checks
Always start by checking the battery. Measure the voltage and have the battery tested under load. A healthy battery delivers at least 12.6 volts at rest at 20 degrees Celsius and must not drop below 10 volts under load. In the C6 a strong battery is extra important because of the electronics.
Then check whether there are any fault codes stored in the system. Diagbox is Citroën’s diagnostic system. With an OBD scan tool or preferably Diagbox you can see whether the ECU has registered any problems. Codes relating to fuel pressure, sensors or the glow system point directly to the cause.
Checking the fuel circuit
If the battery and electronics are in order, focus your attention on the fuel circuit. Start with the fuel filter. A clogged filter causes pressure loss and difficult starting. Replace the filter if it is older than the recommended service interval, or earlier if in doubt.
Also check for air leaks in the system. Air in the fuel line prevents pressure from building up. Pay particular attention to hose connections, seals and the filter head. You eventually get the engine started after extended cranking. After the car has stood still for a day, the problems return. This points to a small air leak.
Measuring rail pressure and pump performance
If the engine does turn over but does not fire, insufficient rail pressure is often the culprit. With diagnostic equipment you can read the actual fuel pressure in the common rail and compare it with the specifications. The 2.7 HDi must be able to build up a pressure of several hundred bar during starting.
If the pressure remains too low, this points to a defective high-pressure pump, a leaking rail or a problem with the pressure control. This requires specialist diagnosis and repair, because the high-pressure system operates under extreme pressure and is not suitable for DIY repairs.
Solutions and prevention
You can prevent many starting problems with proper maintenance and timely replacement of wear parts. For problems that have already arisen, there are usually clear solutions.
Immediate solutions by cause
If the battery is weak, replacement is the best solution. Choose a battery with sufficient capacity, preferably at least matching the specifications of the original battery. If the car is regularly used only for short journeys, consider a trickle charger to keep the battery topped up.
For problems with the glow system, replace defective glow plugs. If in doubt, test all plugs and preferably replace them as a set. Also check the relays and wiring of the glow system.
Fuel pressure problems require a targeted approach. Replace the filter if it is blocked. Seal air leaks in the supply line. Replace the relevant pump in case of wear or failure. If the high-pressure pump is defective, replacement is necessary. This is an expensive repair that should be carried out by a specialist garage.
Preventive measures
Strictly follow the maintenance schedule. Replace the fuel filter on time, especially if the car is used irregularly or stands still for long periods. Diesel fuel contains condensed water, which causes the filter to clog more quickly.
Have engine warning lights investigated immediately. A small deviation quickly grows into more serious damage or complete failure. In the 2.7 HDi small faults in sensors or pressure systems quickly lead to bigger problems.
Test the battery regularly, especially before winter. A weak battery has even less capacity at low temperatures and that can be just the difference between starting and not starting.
When to go to a garage
You cannot solve all starting problems yourself. You have replaced the battery and the fuel filter, but the car still does not start properly. In that case a professional diagnosis is needed. Problems with the high-pressure pump, rail system or electronics require specialist knowledge and equipment.
Go to a garage with experience of Citroën diesel engines and preferably access to Diagbox. Diagbox is Citroën’s diagnostic system and offers extensive diagnostic options. It can show live data for fuel pressure, sensors and actuators, which helps the mechanic find the cause more quickly.
Do not wait too long with repairs if the starting problems persist. Extended cranking can cause damage to the starter motor and battery. In addition, an underlying problem, such as a leaking high-pressure pump, can cause further damage to the engine.
You can find more information about the automatic gearbox of the Citroën C6 in our article on the common problems with the automatic gearbox in the Citroën C6.
Frequently asked questions
The most common causes are voltage problems due to a weak or defective battery and faults in the glow system (glow plugs/preheating), especially noticeable during cold starts. In addition, fuel pressure problems often cause starting issues, for example due to contaminated fuel filters, air in the system or wear of the (high-pressure) fuel pump. Defective or deviating sensors in the engine management can also cause the engine to turn over but not fire. In practice it is often a combination of slight voltage weakness and small deviations in the fuel system or sensors.
Start with the battery: measure the voltage (at least approx. 12.4 V when stationary, above 10 V while starting) and check whether the starter motor turns the engine over briskly. Then use an OBD-II reader to read the fault codes to see whether there are indications of glow plugs, sensors or fuel pressure. Visually check the fuel filter and lines for leaks or air bubbles, and replace an old or unknown filter. Finally, pay attention to whether the problem occurs mainly with a cold or warm engine; if cold it is more likely to be the glow system, if both cold and warm it is more likely to be fuel pressure or sensors.
With the 2.7 HDi engine, problems with the high-pressure fuel pump and the fuel pressure (common rail/rail pressure) are most often mentioned as a cause of starting problems. In addition, defective glow plugs or a fault in the glow control regularly cause cold-start problems. A weak battery or voltage problems can also quickly lead to poor or non-starting with this engine. Finally, defective sensors (such as in the engine management) can prevent the ECU from injecting enough fuel, causing the engine to turn over but not fire.
Have the battery and charging system tested regularly and replace an ageing battery in good time, as the C6 is very sensitive to voltage drop. Replace the fuel filter according to the schedule (or earlier if in doubt) and have the fuel system checked for air leaks and sufficient rail pressure. At early signs such as longer cranking or warning lights, have fault codes read immediately so that emerging problems in the glow system, sensors or high-pressure pump can be tackled quickly. Drive the car regularly for longer trips so that the battery and fuel system remain in good condition.
For a Citroën C6 2.7 HDi the average costs for resolving common starting problems are usually between about €150 and €350 when it concerns the battery, glow plugs or fuel filter / small leaks. If a defective sensor or electronics in the engine management is found, repairs often cost around €200–€500 depending on the component and labour time. For serious problems with the high-pressure fuel pump or rail pressure components, costs can rise to around €800–€1,500 or more. A targeted diagnosis (± €75–€150) is usually the first step to avoid unnecessary replacements.