Eolys pump fault: how the additive pump works and how it fails

What the Eolys system is made of

Eolys is a cerium-based fuel-borne catalyst made by Solvay, formerly Rhodia. PSA uses it in the Peugeot and Citroën diesel particulate filter system. The fluid is stored in a dedicated additive tank beside the fuel tank. A small electric pump draws from it and injects a measured dose into the diesel tank. The engine ECU controls the pump and keeps a running count of how much additive is left.

Once the additive is in the fuel, it travels through the engine and ends up in the soot trapped in the particulate filter. There it lowers the soot ignition temperature from about 600°C to around 450°C. The filter can then clean itself during ordinary driving, without needing the exhaust to get as hot as it would otherwise.

The system has four main parts: the additive reservoir, the pump, the wiring and connector, and the ECU logic that decides when and how much to dose. A fault in any of them can look like a pump fault from the driver's seat.

Two generations of tank, and why it matters

PSA changed the additive hardware over the years. The right fluid and part depend on which you have.

• Older rigid additive tank

  Early systems use a rigid tank holding a fluid such as Eolys DPX42 or Eolys 176. These pumps were simpler, with less electronics, and the ECU controlled them by direct signals.

• Later flexible pouch in a rigid housing

  From around 2010, a flexible pouch sits inside a rigid housing. The fluid is Eolys Powerflex, also known as DPX10. The pouch collapses as it empties, which stops air entering the system.

• Multiplexed pump on later cars

  The newer pump has its own electronics and communicates with the engine ECU over CAN. That is why P1435 describes a CAN network fault or a pump fault.

• Fluids are not interchangeable

  Adding the wrong additive can upset the dosing and damage the filter. We confirm the correct fluid and part from your VIN, never from the model name alone.

Refuel detection and the additive counter

The pump does not run all the time. The ECU looks for a refuel event, using the fuel level signal and, on some cars, the fuel flap. When it sees a rise in the tank level, it commands the pump to inject a dose proportional to the fuel added. Every dose is subtracted from the additive counter held in the ECU.

This means a fault can come from the counting rather than the hardware. If the fuel level sender gives a false reading, the ECU might not detect refuels and so never dose. If the counter reaches its minimum, the ECU stores an additive level code, commonly P15B3 on many PSA ECUs, and shows a dash message. Topping up the fluid does not fix this on its own. The counter has to be reset with diagnostic equipment.

The same applies after fitting a new tank or pump. The ECU has no way to know the hardware has changed until it has been told. A new part that has not been coded and learned will often cause fresh faults.

Signs of an Eolys pump fault

• Stored codes

  P1435, P1434, U0118 or an additive level code. Some tools also show FEB0.

• Dash warnings

  Engine fault, anti-pollution fault or the message about risk of particle filter blocking.

• No additive counter movement after a fill

  A clear sign that the pump is not dosing. We see this in live data when we read the counter before and after refuelling.

• Failed or very frequent regenerations

  The fan runs on after a drive, the idle rises, and fuel economy drops as the ECU struggles to clean the filter.

• Limp mode

  The late sign. By this point, soot has built up and the filter may need a forced regeneration or cleaning.

• Smell or fluid near the tank

  Rare, but a split pouch or perished hose can leak additive. Cerium fluid is oily and can leave a residue.

Do not confuse the Eolys pump with the AdBlue pump

The Eolys pump is small and sits near the fuel tank. Its job is to put additive into diesel. The AdBlue pump is part of the SCR system and sends a urea solution into the exhaust to deal with NOx. They have different parts, different fluids and different codes. Fitting one fluid into the other tank is a costly mistake.

A car with both systems can have a fault on either. P1435 and P1434 point at the Eolys pump. AdBlue pump and dosing faults show as codes in the P20xx range and with AdBlue countdown messages. Our VIN check tells us which are fitted before we begin.

Testing an Eolys pump before replacing it

A pump is replaced only when the tests say it is the fault.

• Identify the generation

  VIN and engine tell us whether the car has a rigid tank, a pouch housing or a multiplexed pump, and which fluid belongs in it.

• Read counter and refuel data

  Before and after a fill, we watch the additive quantity and refuel flag. This shows whether the ECU is seeing refuels and whether the pump is delivering.

• Command the pump

  An actuator test from the tool runs the pump. A clean response and fault status change usually clears the pump.

• Measure supply, earth and CAN

  At the pump connector we check voltage under load, earth quality, and the CAN high and low lines. Faults here are far more common than failed pumps.

• Check the pouch and lines

  We look for a split pouch, perished hoses, air in the system and leaks around the housing.

• Full module scan

  We confirm that no other module is holding a related network fault that could be affecting the pump.

Pump replacement, priming and coding

We diagnose first and agree a fixed price before work begins. No fix, no fee on the agreed outcome.

When the tests show the pump or tank is at fault, replacement is done at your location. We come to your drive, yard, depot or roadside, 6am to 9pm, seven days a week. The new parts are matched to your VIN and carry a written warranty.

• Fit the new pump or pouch assembly

  The old unit is removed, the connectors are checked and replaced if needed, and the new part is fitted securely.

• Fill with the correct Eolys fluid

  We use the additive that matches your system generation, and avoid air entering the lines.

• Prime the system

  Priming makes sure the pump and lines are full and ready to dose. Without it, the first doses are unreliable.

• Code, reset and verify

  The new part is coded with diagnostic equipment, the additive counter is reset, codes are cleared and the pump is test-run before a final road test.

• Mobile diagnosis and basic repair: From £249 Callout, testing and fixes such as connector or wiring repair.
• Pump, pouch or tank replacement with coding: Fixed price after diagnosis Parts confirmed against your VIN and quoted before any work.
• Service regeneration: Quoted on the day Where the filter has loaded up during the fault.

P1435 questions

How long does an Eolys pump last?

There is no fixed life. Many last the life of the car if the wiring stays dry. Connector corrosion and wiring damage usually cause trouble well before the pump wears out.

Can I add Eolys fluid myself?

We advise against it. The wrong type can harm the system, and the additive counter will still need resetting with diagnostic equipment. We fit the right fluid for your VIN.

Why does a new pump need coding?

The ECU has to recognise the new part and start a fresh additive count. Without coding, it may keep the old fault data or refuse to dose.

How is the pouch different from the old tank?

The pouch is a flexible bag inside a rigid housing. It collapses as it empties. The older tank is a rigid container. They use different fluids and parts.

Can a fuel level fault stop the additive pump?

Yes. The ECU uses fuel level changes to spot refuels. A faulty sender can mean refuels are missed and no dose is made, even though the pump is healthy.

Does it matter if I let the additive run out?

It does. The filter then loses its help to burn soot. You may get a level code, a dash message and eventually blocking. Refill and counter reset early are cheaper than a blocked filter.