0445020539 CP4 High Pressure Common Rail Fuel Pump for Mercedes Diesel

The application we stand behind is a Mercedes-Benz commercial vehicle diesel on a common rail system, and the vehicle OE number published for this assembly, A4300700201, points the same way. Two things carry that application and they are the two the published data actually supports: the label number pair on the unit, and the drive end it presents. We deliberately do not extend that to a model list, a cylinder count, an emission stage or a year range, because the sources we can cite contradict each other on exactly those four points and a value we cannot stand behind twice is worse than no value at all. That is the diesel injection pump this engine was built with, and an order that starts from the pump coming off is the one that arrives correct.

Three more identifiers worth having. If the vehicle is still with the customer, the VIN on the registration document settles the engine variant faster than any chart, and the chassis plate number settles which build the vehicle left the factory as. Where the pump is already off the engine, a photograph of the engine code plate and a photograph of the label on the pump settle it instead. Any one of those three alongside the label on the pump is enough for us to confirm in writing; all of them together is what stops a number-range mix-up reaching your workshop.

Why the label matters more than the number range. A Bosch distributor catalogue publishes the whole 0 445 020 5xx range as high pressure pumps, and it documents numbers from that range against different engines entirely. That tells you the family and nothing about your vehicle. The label tells you the rest: the type-part number on the top line, the type designation on the second, the service code beneath. Match those, confirm the four-bolt flange and the central spigot, confirm the metering connector, then order. A high pressure common rail pump bought that way arrives right the first time, which is the whole point of the four steps above.

What this page is not claiming. We are not saying that a neighbouring number in the same range fits your engine, that a component number for the metering unit is settled, that the published application covers a vehicle without a label check, or that a pump from a different family substitutes. 0 445 020 539 describes one build, and the label on the unit is what identifies it. Anything beyond those lines is better answered from your own parts data, and we would rather answer it with you than assert it here.

On a common rail diesel the low pressure and high pressure sides of the fuel system are separated. A lift pump in the tank pushes fuel forward at low pressure. The high pressure common rail fuel pump is what comes next, and it decides everything after that point: it raises the fuel to rail pressure inside its own body, and a metering unit on the housing decides how much of that pressure the engine is actually allowed to have, on a signal from the engine control unit. Rail pressure is therefore produced mechanically and controlled electrically, and on this pump the two halves fail in quite different ways.

The architecture is where most ordering mistakes start on this number, and the mistake has an expensive shape. A distributor pump is driven by a lobe inside the engine block: the lobe rotates, it pushes a plunger down, and the volume above the plunger is forced into the line. A CP4 pump works the other way round. The high pressure element is integrated into a housing with its own camshaft, and that camshaft is driven off the engine by a belt, a chain or a cogwheel, moving the pistons that generate the pressure. Same result at the rail, entirely different machine, and the two are not interchangeable at the flange, at the connector or in the service routine. Bosch publishes the CP4 family as modular, built around one or two such elements, and describes the delivery as demand based with a return path to the tank on a second low pressure connection.

The second thing that follows from the architecture is lubrication, and it is the most practically useful thing on this page. On this pump the diesel fuel itself is what lubricates the high pressure element; there is no separate oil feed to the pump. That is why fuel quality matters more here than on a mechanically lubricated pump, and it is why a failure can put wear metal into the fuel circuit instead of only stopping the pump. A replacement fitted into a circuit that was never flushed can therefore be destroyed within its first hour, by metal that was already loose in the tank. That is the single most expensive thing that can go wrong on this job, and it is entirely avoidable.

The numbers are the second trap. A Bosch distributor catalogue publishes the 0 445 020 5xx range as high pressure pumps, and it documents individual numbers in that range against different engines, so the range tells you the family and nothing about your vehicle. The label is the answer: 0 445 020 539 on the top line, a Bosch type designation beginning CR and CP4 on the second, a service code and a matrix code beneath. A separate published interchange group exists for this number, and where we cannot corroborate the other members from a second independent source we do not reprint them as fitments. The page therefore anchors on the label rather than on the listing number you found us through.

Once fitted, the rail feeds every injector on the engine from one common volume, which is what makes it efficient and also what makes it expensive when it fails. One pump feeds the whole engine, so a fault is not confined to one cylinder the way a single worn injector is. The engine loses pressure across the board, and the diagnostic picture looks like a fuel system problem rather than a component problem. Our fault code guide covers how to read the codes that come with that, and the point of it is always the same: read the scan data against target, not the code name.

When the pump stops behaving, the engine tells you through how it runs rather than through a warning light. A hard start that is worse when the engine is warm. An idle that hunts and will not settle. Power that arrives fine at idle and disappears the moment the engine is worked. Each of these is examined properly in the symptoms section below, together with the rail pressure comparison that separates a metering fault from a mechanical one without guesswork.

Where our supply differs is what arrives rather than how the part works. Original equipment supply comes through the manufacturer’s own channels, and a buyer whose paperwork requires a factory boxed part does need to go there. What we supply is a high pressure pump replacement — a new compatible unit for the same job, sold under the Vidishi Auto brand, labelled with the same type-part number, at a single-piece minimum with no core return. That last point matters on this job more than on an old mechanical injection system: nothing has to come back, there is no exchange loop to manage, and the removed pump stays with you for the warranty file.

One thing we do not do is dress that up. The 0445020539 pump we ship is ours, not a manufacturer’s and not a vehicle maker’s. The part numbers, the family name and the vehicle OE number appear on this page so you can match the pump you are replacing. They are references for fitment, not a claim about who made the part, and the label and casting marks visible in the photography are recorded as markings carried by the photographed goods. The country-of-origin line printed on that label belongs to the label; it is not a statement about where the goods we supply were made, which is why no country of manufacture is claimed anywhere above. The buying guides hold the general method for confirming any diesel part from the unit itself, and the glossary explains the terminology if any of the names above are unfamiliar.

How we label data. Confirmed means a value read directly from the goods we handle, including the numbers on the data label and the drive end and connectors visible in the photography. Reference means a part number, a family designation or a cross reference quoted so your paperwork can be matched, and carrying no claim about origin. Not published means the field is left blank on purpose — a pressure figure, a component number or a fitment list that we cannot source would be worse than an empty cell, because it would end up in somebody’s parts order or somebody’s engine settings.

What is in the box. One complete high pressure common rail fuel pump: the cast housing with the high pressure element and its own camshaft behind the covers, the four-bolt mounting flange with the polished drive spigot, the capped line stubs, the electrical connectors for the metering unit, and the covers and plugs as photographed. New sealing washers and a fresh filter element are required at fitting and neither is asserted as included for this line. Nothing on this page is sold loose from the pump, and internal service components keep their own listings for buyers who want a rebuild rather than a replacement. Whether the metering valve itself is supplied fitted is confirmed against the packing list rather than claimed here, because a published catalogue lists a fuel quantity control valve as a separate service part against a closely related number.

Read the table from the top, because the order matters. 0445020539 is the supplier part number and it is the weakest identifier on the page: it is the number a listing carries, and it tells you nothing about which build you have been sent. The row that identifies the unit is the 0 445 020 539 printed on the top line of its own label, with the Bosch type designation on the line beneath it, and those are the two you will find on the metal in your hand. Used as a 0445020539 cross reference map, the table is a boundary as much as a bridge. A parts system will match one form of a number and not the other, which is worth knowing before a search box tells you the part does not exist.

The Bosch CP4 row is there for identification the way a family name is on any catalogue entry, and it is worth reading with care. It tells you which published pump family this architecture belongs to, which narrows the search and tells a parts clerk what sort of unit to look for on the shelf. It is not a statement that the unit in our box was made by that manufacturer, because it was not, and the difference matters both legally and practically when a warranty claim has to be settled. Our brand page sets out how we handle reference brands across the site and what that does and does not claim.

The three range-boundary rows are the half of the mapping that stops people over-reaching, and they are here for a reason. A Bosch distributor catalogue publishes the 0 445 020 5xx range as high pressure pumps and documents individual numbers inside it against different engines, including the neighbouring 0 445 020 515 with a Mercedes-Benz vehicle number and the neighbouring 0 445 020 538 against a different application altogether. Same range, different engines. That is exactly why a number-range search is not a fitment check, and why the label on the unit settles the match instead.

What the table deliberately does not do is extend itself. It does not say that a neighbouring number fits your engine, that a component number for the metering unit is settled, or that a pump from another family substitutes. A published interchange group does exist for this number, and we have left its remaining members out on purpose, because only one source carries them and we will not turn a single seller’s grouping into a fitment claim. Those are exactly the assumptions that turn a cheap order into an expensive week of vehicle downtime, and we would rather leave the cell empty than fill it with a guess. Our comparison charts set out the number families we can evidence, and the buying guides cover the general method for confirming any diesel part from the unit itself.

The practical difference shows up on the pressure test. When a rail reading will not reach target under load, the vehicle either runs on compromised pressure until something else breaks, or the workshop fits a known-good pump and the reading comes straight back. Keeping a matched spare — correct label, correct four-bolt flange, metering connector present — turns a two-week vehicle stop into a same-week swap. That is the case for holding one of these before anything has failed, and it is why a single-piece minimum is the sensible purchase here: one pump is one job, and the shelf spare is the one that earns its keep.

• Hard starting that is worse when warm — A metering unit that is slow to respond lets rail pressure fall away as the engine heats up, and a common rail engine needs pressure to start, not only to run. A start that is brisk cold and long hot is a signature worth reading properly.
• An idle that hunts or will not settle — At idle the rail pressure has to be held steady for every cylinder at once. A pump that cannot hold it shows up as an idle that will not hold, often with a shake that no mounting fault explains.
• Loss of power only when the engine is worked — When the operator asks for load the rail pressure has to rise, and that is the demand a tired pump struggles to meet. The engine feels flat exactly when it is asked for more, and fine at idle, which is what makes it easy to misread.
• Smoke under load — Fuel delivered at a pressure the engine asked for and not the one it got will not atomise the way it should, and it leaves the stack as smoke. On a pump of this type that points at the metering side and the high pressure element, not only at the injectors.
• Rising fuel consumption — Fuel that returns past a metering unit that has drifted is measured again and again, so the gauge moves faster than the work done and the tank empties sooner than the hour meter suggests.
• Rail pressure that will not reach target — The measurement that settles it. A scan tool reading actual rail pressure against target, compared at idle and then under load, points at the pump when actual sits persistently below target and no filter or injector work changes the reading.
• Metal in the filter bowl after a failure — On this architecture the diesel itself lubricates the high pressure element, so a failure can put wear metal into the fuel circuit rather than only stopping the pump. Fine particles in the filter bowl or a return line running unusually hot are the reasons to stop and flush rather than fit and drive.
• A fault code on the pressure side — A low pressure code reported on the rail, and a regulator or performance code for rail pressure, both belong on the list. Read the scan data rather than the code alone, because a code names a circuit and not always the part.

The pattern worth holding on to is the one that affects every cylinder together. A single worn injector shows up on one cylinder and leaves the engine steady on the other three. A tired high pressure fuel pump takes the whole engine down together, because one pump feeds the whole rail. That single distinction does more diagnostic work than any code name, and it is why we would rather you bring us a pressure reading than a code you have decoded from a list. The fault code guide explains how to read the data behind the code, and our maintenance guide covers the filter and water separator intervals that keep this circuit healthy.

The second pattern is specific to this architecture and worth its own paragraph, because it changes what you do next. Where the fuel itself lubricates the high pressure element, a failure can send wear metal through the tank, the lines, the rail and the filter housing along with the low pressure that stopped the engine. Fine particles in the filter bowl, or a return line running unusually hot, are the reasons to stop the engine and flush the circuit rather than fit the pump and hand the vehicle back. A replacement fitted into a circuit that was never cleared is a second failure bought on the same day.

• Step 1. Drain, depressurise and mark the drive position
  Let the engine stand, release residual pressure, and before anything is unbolted mark the position of the pump against its mounting flange. This pump is driven through a coupling, and the mark is the only thing that guarantees it goes back on the same position.
• Step 2. Flush the whole circuit if the old unit failed internally
  On this architecture the fuel lubricates the high pressure element, so a failure can leave wear metal in the tank, the lines, the rail and the filter housing. Drain all of it, fit new filters, and only then fit the new unit. This step is the single biggest cause of a second failure and it is the one most often skipped on a pump that is sold as a drop-in.
• Step 3. Clean the mounting face and the spill port before opening anything
  Wash around the pump, blow the sealing face down, and only then release the bolts. Grit that falls onto that face ends up between the two surfaces, and the new pump will weep from its first minute.
• Step 4. Unbolt evenly and support the housing
  Work the bolts in sequence rather than freeing one corner at a time. The housing has to lift straight off the engine, not at an angle, and the spigot must never be levered against the drive coupling.
• Step 5. Inspect the spigot, the coupling and the surrounding material
  Check the spigot, the coupling and the surrounding material for wear, burrs and stray debris. A drive that has been turning against a worn coupling, or against one that has picked up metal, will damage the new pump in its first hour of running.
• Step 6. Fit new seals and a fresh filter element
  A fresh seal goes under the refitted pump and the filter element is renewed rather than reused. Reused seals and a reused element are the most common causes of both a weep and an early return of the same fault.
• Step 7. Refit square and torque to the engine figure
  Drop the pump into the marked position, bring the mount up evenly, and torque to the figure for your engine. The figure belongs to the engine, not to the part, and we do not publish it for this number.
• Step 8. Prime, bleed and verify before the engine goes back to work
  Fill and bleed the system properly until it shows no air, then confirm the metering connector is fully seated and the protective caps are off every port. Verify rail pressure against target at idle and under load before the vehicle leaves, and check the filter bowl again after the first run.

Two notes on what we deliberately do not print. We do not publish the tightening figure for the mount, the rail pressure figure, or the drive phasing, because all three belong to the engine application rather than to the part, and a figure copied from a product page into a workshop manual is how a good pump gets damaged on a correct fit. Take them from the engine manual for the vehicle in front of you. And we do not publish a diesel fuel injection torque figure as a shortcut, because the mount, the lines and the rail connection each have their own value and they are not interchangeable. The installation guide covers the surrounding routine, and the glossary defines the terms if any of the above are new to you.

Every 0445020539 pump is covered by a 12-month warranty against manufacturing defects. That covers a unit that arrives out of specification or fails early because of how it was made. It does not cover damage from contaminated fuel, from water in the system, from a filter changed too late, from incorrect fitting, from a drive coupling torqued beyond its figure, or from a separate fault elsewhere in the fuel circuit. It does not extend to labour or to the vehicle. It is a supplier warranty from Vidishi Auto and it is not a Bosch warranty and not a Mercedes-Benz warranty — we are not a dealer for any of the equipment makers and no cover from any of them travels with this part.

The one condition we ask about every time is whether the circuit was flushed when the old unit came out, because on this architecture that is the single most common reason a replacement pump fails early and the single easiest thing to get wrong on a job where somebody is under time pressure. The fuel lubricates the high pressure element, so metal left in the circuit is the mechanism, not a theory. Tell us what was done and we can tell you quickly whether a claim is likely to stand. If you would rather settle that question before you order, the contact page is the fastest route to a written answer.

The minimum order quantity is 1 piece, and the reasoning is worth stating rather than leaving you to work out. Demand for a pump of this type arrives one fault at a time, because a failure takes a vehicle off the road and the repair is done once, properly. A single unit covers that job, and it lets one pump sit on the shelf as the known-good unit for pressure testing before anything else is committed. From there the line scales normally — a fleet running several engines will take a set per vehicle, and a distributor will take them alongside the rest of a fuel system order.

What we do not do on this line is pretend the part is something it is not. The unit we ship is a new compatible replacement sold under the Vidishi Auto brand. It is not Bosch-branded, it is not Mercedes-Benz-branded and it is not a factory boxed original. That matters commercially as well as legally: if your incoming goods inspection needs a specific brand on the paperwork, this is not that product, and we would rather tell you now than have a delivery rejected. The brand page sets out the distinction, and the help centre covers ordering and documentation questions.

The package size and gross weight in that table are a packing estimate, and we label it that way rather than quietly presenting it as a specification. No source we can stand behind publishes a packaged figure for this number, so we give you a figure we can pack and weigh against rather than a manufacturer specification we cannot evidence. If your freight is calculated on volumetric weight rather than actual weight, tell us the destination and we will confirm the chargeable weight against the carton we actually use. The shipping page sets out the full documentation and delivery terms, and the order tracking page is where to follow a shipment once it has left.

On the protective side, the two areas we watch are the drive spigot and the electrical connectors on the body. A spigot knocked out of register will not seat properly on the coupling and will damage the new pump within hours, and a bent connector pin is a fault that looks like an electrical problem for weeks afterwards. Both are packed protected on every unit, and both are worth checking on arrival before the box goes into stores.

A high pressure common rail pump is a small number of large, precisely machined parts, so this line is checked at unit level rather than by sample. Every batch passes an incoming check for the numbers on the data label, an inspection of the four-bolt mounting flange and the polished drive spigot, a confirm that the metering connectors and the black electrical plug are present, undamaged and capped, a check that the line stubs and the threaded port are clean and free of obstruction, and a packed-weight confirmation against the documented figure. The supplier shows an ISO 9001 system certification badge on the product photography, which we record as a supplier statement rather than as a certificate we issue.

Rather than publish reviews we cannot verify, we tell you what we will actually put in writing: a written fitment confirmation against the label you send us, a written quote against your quantity and destination, and a warranty position on any claim that follows. If you need a supplier who will sign a specific inspection or conformance document with the order, ask before you buy rather than after, because the answer depends on what the document is. The help centre covers the documentation we can provide, and the partner programme page is the route for a standing arrangement that needs more than a one-off order.

Support is not an add-on on this line — it is how most of these orders get placed correctly. It costs nothing before you buy: send the numbers read off the data label of the unit you are removing, the engine code and the vehicle details, and we check the whole set against what we supply before quoting. That last item is the one people skip, and it is the one that matters most here, because a published number range tells you the family and not the vehicle, and the published fitment fields for this number contradict each other. Two minutes with the label in front of you is cheaper than a pump that arrives and does not settle the fault.

Two things we will not do, whatever the order size. We will not quote a fitment we cannot evidence, and we will not ship a pump matched on a number range when the label on the old unit is available. If that costs us an order, it is still the right call: a high pressure pump that arrives mismatched costs a workshop a second removal, and that is the failure we exist to prevent. If anything on this page is unclear, the contact page lists every route to us, and a written answer is always better than a guess on a workshop schedule.