Citroën Relay P1435: tracing an additive pump fault on a working van

Relay engines and the additive question

The Relay is built by Sevel with the Peugeot Boxer and Fiat Ducato. Older 2.2 HDi vans, and some 2.0 and 2.2 BlueHDi Euro 6 vans from 2016, may use an Eolys fuel-borne catalyst. Other versions use a catalysed particulate filter that needs no additive tank at all.

We never assume. On every Relay we check the VIN and build first, then tell you which filter system the van really has. If there is no additive system, P1435 is not the cause of your problem and we look elsewhere.

Euro 6 Relays may also have AdBlue. That is a separate system with its own tank, pump and codes, so the two warnings are unrelated unless diagnosis shows otherwise.

Tank and pump position on the Relay

The additive hardware sits low, beside the fuel tank, which puts it in the line of fire from every wet road.

• Load bays and tail lifts

  Relays used for parcel, furniture and pallet work often carry tail lifts and extra underbody equipment. Fitting that gear is a common moment for the pump loom to be clipped, moved or nicked.

• Long runs of wiring

  On long wheelbase and high-roof Relays the loom is a long run along the chassis. Chafe points multiply, and a single rubbed CAN wire is enough for P1435.

• Salted roads and wet yards

  Delivery vans live outdoors in all weathers. Road salt creeps into the plug, the pins corrode, and the CAN signal becomes unreliable before the supply fails.

• Refrigerated and ambulance-style conversions

  Added power supplies and wiring around the rear chassis can interfere with the tank area. We check any conversion wiring that runs near the pump.

What a Relay driver notices

Fleet drivers rarely report a code. They report a van that has gone flat on the motorway with a full load, or a dash message about the anti-pollution system. A loaded Relay in limp mode will crawl at around the speed of a lorry and the cooling fan may run on after a stop.

Some Relays also store a low additive level, shown as P15B3 on many ECUs. That is a different job from P1435. A van can have a perfectly good pump that has simply run out of fluid, or a full tank behind a pump that cannot communicate. We read the live additive quantity to tell them apart.

If your driver has already had a regeneration fail, tell us. It helps us judge how much soot is sitting in the filter.

What makes a Relay different to diagnose

The Relay shares electronics with the Boxer and the Ducato, so tools sometimes label the same module differently. A fault that looks like an additive problem on the screen can be a gateway or network issue in another module. We scan everything and compare, rather than trusting one line of text.

Fleet history also matters. Relays often pass through several hands and workshops, so a pump may have been swapped without coding. We check for that. The sister van, the Peugeot Boxer, has its own P1435 page.

Relay additive versus AdBlue

The Eolys additive and AdBlue do two separate jobs on a Relay. Eolys goes into the diesel and helps the filter burn off soot. AdBlue goes into its own tank and cleans NOx in the exhaust on Euro 6 SCR versions.

A P1435 fault will not be fixed by filling AdBlue, and an AdBlue countdown will not be fixed by adding Eolys. If your dash shows both, treat them as two jobs. We can look at both in one visit.

How we diagnose P1435 on a Relay

We attend the van where it is working, and test with the tools and meters needed to prove the fault.

• VIN and system check

  We establish whether this Relay has an Eolys tank and pump, and which version, before testing anything else.

• Full network scan

  We read every module for U0118 or lost-communication codes and compare timing with the engine ECU's record.

• Additive and soot data

  Live additive quantity, refuel detection, soot mass and pressure readings show whether dosing is happening.

• Pump response test

  A commanded pump test shows whether the unit works when it has proper power and communication.

• Electrical checks at the plug

  We measure supply, earth and CAN voltages and resistance at the connector, ruling a loom fault in or out.

• Underbody inspection

  Loom routing, conversion wiring, tank, pouch and joints are inspected for damage or contact.

Relay P1435 repair and pricing

Diagnosis comes first. You then get a fixed price before any work starts, and no fix means no fee on the agreed outcome.

We are mobile and come to your drive, yard, depot or roadside between 6am and 9pm, 7 days a week, including bank holidays. Keeping a delivery van off the road for as short a time as possible is the point, so we aim to fix on the first visit and give a written warranty on the work.

• Connector and wiring repair

  Sealed repairs to damaged wires, new pins or a pigtail where corroded, and the loom secured clear of the chassis.

• Additive pump or tank replacement

  Only after wiring is proven. We prime, code and test the new part.

• Refill and additive counter reset

  The right Eolys fluid for the tank type, then the counter reset with diagnostic equipment.

• Service regeneration and test drive

  Where soot has built up, we regenerate the filter and road test to confirm a clean result.

• Mobile diagnosis and simple repair: From £249 Callout, full diagnosis and fixes such as a connector or loom repair.
• Additive pump or tank assembly: Fixed price after diagnosis Quoted once the cause is proven, not on the code alone.
• Regeneration on a heavily loaded filter: Quoted on the day Depends on the soot mass we find.

P1435 questions

Do all Citroën Relays use Eolys?

No. Some Relays use a catalysed particulate filter with no additive. Fitment varies by engine and year, and we confirm by VIN before any additive part is discussed.

What does a low additive level on a Relay mean?

Many ECUs show P15B3 for additive level below minimum. It means the tank needs a refill and reset, which is different from the pump communication fault in P1435.

Can you attend a Relay on a tail lift or with a body fitted?

Yes. We work around the body, but we may need clear access under the van near the tank. Tell us about the conversion when you book.

My Relay has been in limp mode with a full load. Is the filter damaged?

Not necessarily. Limp mode protects the filter. We read the soot mass and pressure, then tell you whether a regeneration is enough.

Is a Relay P1435 fault covered by the fleet service?

We offer fleet accounts for vans, with a fixed price per vehicle after diagnosis. Ask when you call.