P1435 on Peugeot and Citroën: the Eolys additive pump fault explained

What P1435 means on a Peugeot or Citroën

PSA diesels with a particulate filter (Peugeot calls it FAP, filtre à particules) use a fuel additive to help the filter clean itself. The additive is cerium-based fluid sold under the Eolys name. A small pump, fitted to a separate additive tank next to the fuel tank, injects a measured dose into the diesel every time you refuel. Once mixed into the fuel, the cerium lowers the temperature at which trapped soot burns, from roughly 600°C to around 450°C. That is what lets the filter regenerate on normal UK roads.

On later systems the pump is multiplexed. It does not just receive a simple on/off signal. It has its own electronics and talks to the engine ECU over the CAN network, reporting its status and receiving dosing commands. P1435 is the code the engine ECU stores when that conversation breaks down or when the pump reports that it cannot do its job. Most diagnostic tools word it as "Multiplexed additive pump: CAN network fault or pump fault". The wording varies slightly by ECU and tool, so we always read the manufacturer description, not just the number.

Because the code covers both the network and the pump, it does not tell you which part has failed. A corroded plug under the car, a blown fuse, a chafed CAN wire and a failed pump can all set the same P1435. That is why replacing the additive pump on the code alone is the most common expensive mistake we see.

P1435 vs P1434: what is the difference?

The two codes often appear together. They point at the same pump but describe different failures.

• P1435: communication or pump-reported fault

  The ECU cannot talk to the multiplexed pump properly, or the pump has told the ECU it has a fault. Think network first: CAN high and low wires, the pump's own supply and earth (without which it cannot talk at all), then the pump electronics.

• P1434: pump supply or control circuit

  Usually reported as an additive pump circuit or power supply fault. The ECU sees an electrical problem in the circuit that feeds or controls the pump. A fuse, relay feed, broken wire or corroded connector is more common than a dead pump.

• Why they appear together

  A pump with no 12 V supply cannot communicate either. So a single blown fuse or a wet connector can set P1434 for the supply and P1435 for the lost messages at the same time. Fix the supply and both often clear.

• Companion codes

  U0118 (lost communication with the fuel additive control module) is the generic network code for the same loss of contact, often stored in another module. Some tools also show manufacturer network codes such as FEB0 and soot codes such as P2463 or P2002 once the filter starts loading up.

Symptoms of P1435

Drivers rarely see the code itself. They see the knock-on effects on the particulate filter.

• Engine management or service light

  The engine warning lamp comes on. Many PSA dashboards also show a spanner or a message about the anti-pollution system.

• "Risk of particle filter blocking"

  A common PSA message once dosing has stopped. The filter is collecting soot faster than it can burn it.

• No regeneration

  Without additive the ECU may stop attempting regenerations, or they fail part-way. Soot loading rises on every journey.

• Reduced power or limp mode

  When soot loading or exhaust back-pressure gets too high, the ECU limits power to protect the engine and filter. Vans often feel it first on hills or loaded.

• Higher fuel use and idle changes

  Repeated failed regenerations use extra fuel. Some drivers notice the idle rising or the cooling fan running after a short trip.

• No symptom at all, yet

  On some vehicles the code sits stored for weeks before the filter loads up. That is the cheapest time to fix it.

Most common causes, in order of likelihood

This is the order we find them in on UK Peugeot and Citroën diesels. Salt, water and road spray under the car drive most of it.

• 1. Corroded or water-logged pump connector

  The additive pump plug sits under the car beside the fuel tank. Water gets past a perished seal, the pins green up, and the CAN signal or supply drops out. Cleaning and resealing, or a new connector pigtail, fixes a large share of P1435 faults.

• 2. Damaged or chafed wiring

  The loom runs along the underside to the tank. We find it rubbed through on brackets, damaged during exhaust or tank work, or chewed by rodents. A CAN wire shorted to earth or to the other CAN wire will set P1435 immediately.

• 3. Lost supply or earth

  A blown fuse, a poor earth point or a fault in the feed from the fuse box. With no power, the pump goes silent on the network, so P1434 and P1435 often log together.

• 4. Failed additive pump electronics

  The pump itself can fail internally, especially on older pouch-type tanks. We only call this once supply, earth and CAN have been proven good at the pump connector.

• 5. Pump problems caused by the fluid

  An empty pouch, the wrong additive type, or air in the system after a refill can make the pump report a fault. The pouch can also split, which drains the fluid.

• 6. Software, coding or a replaced part not learned

  After a pump, tank or ECU change, the new part must be coded and the additive counter reset. Skipping that can leave P1435 or related additive codes stored.

Eolys is not AdBlue

This is the most common confusion we see on PSA vehicles, and it costs owners money. Eolys and AdBlue are two separate systems with separate tanks, separate pumps and separate fault codes. Many Euro 6 Peugeot and Citroën diesels from around 2014 onwards have both fitted at once, so both warnings can appear on the same vehicle.

Eolys is mixed into the diesel to help the particulate filter burn soot. AdBlue is sprayed into the exhaust to turn NOx into nitrogen and water. P1435 belongs to the Eolys side. AdBlue codes such as P20EE or P20E8 belong to the SCR side. Topping up AdBlue will never clear P1435, and an Eolys refill will never clear an AdBlue countdown.

How we diagnose P1435 with live data

Every step is done at your vehicle with manufacturer-level diagnostics. Nothing is replaced until the fault is proven.

• Confirm the vehicle and the system

  We check the VIN, engine and build to confirm an Eolys system is fitted and which type it is. Additive type and pump design differ by generation.

• Full scan of all modules

  We read the engine ECU and the network modules, not just engine codes. P1435 with U0118 in another module tells a different story from P1435 on its own.

• Live data from the additive system

  We read pump status, the additive quantity counter, refuel detection, soot mass and differential pressure. That shows whether the pump has been dosing and how loaded the filter already is.

• Pump actuator test

  We command the pump to run from the diagnostic tool. A pump that responds and doses rules out a dead pump straight away.

• Supply, earth and CAN at the connector

  We measure 12 V supply and earth under load at the pump plug, then check CAN high and low voltages and line resistance. This separates a wiring fault from a pump fault with numbers, not guesswork.

• Visual check under the vehicle

  We inspect the connector, loom, tank, pouch and lines for corrosion, damage and leaks before deciding on the repair.

Typical repair path and what to expect

You get a fixed price before work starts. We diagnose first, then agree the repair with you. No fix, no fee on the agreed outcome.

Most P1435 jobs are finished in one visit to your drive, yard or roadside. Where a new pump or tank assembly is needed, we confirm it on the first visit, give you a fixed price, and return to fit and code it. You keep driving carefully in the meantime unless the filter is close to blocked, which we tell you on the day.

• Connector or wiring repair

  Corroded pins cleaned or replaced, damaged CAN or supply wires repaired with sealed joints, and the loom secured away from wear points.

• Additive pump or pouch tank replacement

  Only once wiring is proven. The new part is fitted, primed, coded and checked with a pump test.

• Refill and counter reset

  The correct Eolys additive for your system is added and the ECU's additive counter is reset, so the dash stops reporting a low level.

• Regeneration and road test

  If soot built up while dosing was off, we run a service regeneration, clear the codes and confirm on a test drive that nothing returns.

• Mobile diagnosis and straightforward fix: From £249 Callout, full live-data diagnosis and fixes such as a connector or wiring repair.
• Additive pump or pouch tank assembly: Fixed price after diagnosis Quoted only once supply, earth and CAN are proven good.
• Service regeneration if soot is high: Quoted on the day Only needed when the filter has loaded up while the additive was not dosing.

P1435 questions

What does P1435 mean on a Peugeot?

It is a multiplexed additive pump fault: the engine ECU has lost reliable CAN communication with the Eolys additive pump, or the pump has reported an internal fault. The cause is often a corroded connector or wiring, not the pump itself.

What does P1435 mean on a Citroën?

The same as on a Peugeot. Citroën and Peugeot share the PSA additive system, so P1435 points at the multiplexed additive pump and its network wiring on both makes.

Is P1435 an AdBlue fault?

No. P1435 belongs to the Eolys particulate filter additive system. AdBlue is a separate exhaust system with its own codes such as P20EE. Some PSA vehicles have both, which is why they are often confused.

Can I keep driving with P1435?

Usually for a short time, carefully. Without additive the particulate filter loads up faster, and if it blocks you face limp mode and a much bigger bill. Get it diagnosed as soon as you can.

Will clearing the code fix P1435?

No. If the wiring or pump is still faulty, the code returns on the next drive cycle. Clearing it also hides the history we use to diagnose the fault.

Does P1435 always mean a new additive pump?

No. Connector and wiring faults are more common than failed pumps. We prove supply, earth and CAN at the pump plug before we ever quote a pump.