Mercedes Specialist St Helens: Independent Mercedes-Benz Servicing, Diagnostics, Coding and Repairs
An independent Mercedes specialist services and repairs the A, B, C and E-Class, the GLA, GLC and GLE, the Vito and Sprinter and the older models to the manufacturer schedule, reads and codes them on manufacturer-level diagnostic software, and deals with the faults the badge is known for: the OM651 timing chain and injector seals, the OM642 swirl flaps and oil cooler, AdBlue and DPF on the diesels, the 7G-Tronic gearbox, the electrics and the modules, without dealer pricing. That is what we do at Boundary Road, and this page sets out what is covered, what goes wrong on each engine, and how a visit runs.
Mercedes specialist St Helens • start here
What does an independent Mercedes specialist do that a general garage does not?
An independent Mercedes specialist services and repairs Mercedes to the manufacturer schedule, with parts and oil to Mercedes specification and the work recorded in the digital service book, so the warranty stays intact, reads and codes the car on manufacturer-level software rather than a generic reader, and knows the engines and the electronics well enough to catch the faults Mercedes is known for before they become engines or modules.
- A and B Service to the Mercedes schedule, with the low-ash oil the engines are rated for, the service indicator reset and the digital service book updated.
- Manufacturer-level diagnostics and coding, so a warning is traced to the module that logged it, and injectors, batteries, modules and keys are coded to the car when replaced.
- OM651 diesel timing chain and injector seal work, caught at the rattle or the chuffing stage rather than after it lets go.
- OM642 V6 diesel swirl flaps, oil cooler seals and turbo actuators, done properly rather than blanked or deleted.
- AdBlue, NOx sensor and DPF faults, repaired and regenerated, never deleted, and the countdown cleared before it stops the car.
- 7G-Tronic and 9G-Tronic gearboxes, oil and filter serviced and the conductor plate and valve body diagnosed before a gearbox is quoted.
- Electrics, modules and ECU faults, from a SAM module to a battery that will not sleep, traced on the network rather than swapped.
What you get that a dealer does not is the conversation: what the reading means, what it costs and what can wait, before anything is done. Send the registration through the reg check below or ring 01744 808586; we look up the engine and its known points before you arrive. The pages linked through this one go deeper: Mercedes servicing for the schedule, Mercedes diagnostics for the fault-finding side, and Mercedes ECU coding for the coding and module work that brings most owners to an independent.
What is covered
What a Mercedes specialist covers at Boundary Road
Everything below is done here, on the ramp, by technicians who see Mercedes every week. Nothing is sent to a dealer.
- A Service and B ServiceTo the Mercedes schedule for the model and year, with the oil specification the engine is rated for and the digital service book updated. See Mercedes A Service and Mercedes B Service.
- Manufacturer-level diagnosticsEvery module read, live data watched, and the fault named before a part is quoted. See Mercedes diagnostics.
- ECU coding and module workInjectors, batteries, modules and keys coded to the car, and the ECU and SAM faults that a general garage cannot touch. See Mercedes ECU coding.
- Timing chain replacementOM651 and the petrol chains, tensioners and guides as a set, at the rattle stage. See Mercedes timing chain replacement.
- Injectors, seals and glow plugsOM651 injector seals and the injectors themselves, coded to the car, and glow plugs removed without snapping. See Mercedes diesel injector replacement and glow plug replacement.
- AdBlue, DPF and EGRNOx sensors, AdBlue injectors and pumps, forced regeneration and off-car cleaning, EGR valves and coolers. See Mercedes AdBlue diagnostics and repair, Mercedes DPF cleaning and Mercedes EGR valve replacement.
- Turbo and swirl flapsTurbos with their oil feeds and actuators, and the OM642 swirl flaps and oil cooler seals. See Mercedes turbo replacement and swirl flap replacement.
- Gearbox and clutch7G-Tronic and 9G-Tronic oil services, conductor plates and valve bodies, and the manual clutches. See Mercedes gearbox repair and Mercedes clutch replacement.
- Suspension, air suspension, brakes and alignmentBushes, arms and dampers on heavy cars, Airmatic on the E, S and GLE, and the alignment printout. See Mercedes suspension repair and air suspension repair.
- MOT testingOn our own lane, with the repairs done in the same building. See MOT St Helens.
The service indicator in the cluster is where most Mercedes visits start, and a typical week is an OM651 diesel in for the chain listened to, the injector seals checked, the AdBlue system read and the B Service done in one visit. Mercedes come from further than most, because coding and module work is not something every garage can do and because the alternative is a dealer bill.
If yours is under manufacturer warranty, that changes nothing here: the schedule, the parts and the digital service book are the same, and the warranty stays intact. The section further down covers exactly why.
Send us your reg. Get a real price back.
No forms, no callback queue, no "prices from". Type your registration, tell us what the car is doing, and press send. It opens WhatsApp with the message already written, and a technician in the St Helens workshop picks it up.
- ✓Your MOT due date looked up for you, so you aren’t guessing.
- ✓A real price for the repair your car needs, not a range.
- ✓The next free slot at Boundary Road, Saturday mornings included.
- ✓Answered by the workshop in St Helens. Never a call centre.
Check your registration
Ten seconds. No account, no waiting on hold.
Send it on WhatsAppor call01744 808586
Mon–Fri 8:30am–5pm • Sat 9am–12:30pm
Engine by engine
What goes wrong on each Mercedes engine, and what we do about it
Every Mercedes engine has its known points. These are the ones that bring cars to Boundary Road most often, with the fix in plain terms.
| Engine and models | What you notice | What it usually is | What we do |
|---|---|---|---|
| OM651 2.1 and 2.0 diesel: A, B, C, E-Class, GLA, GLC, Vito, Sprinter, 2009 on | Rattle on cold start, timing fault | Timing chain, tensioner and guides wearing | Chain, tensioner and guides as a set. See Mercedes timing chain replacement |
| OM651, all models | Chuffing noise, diesel smell, black crust round an injector | Injector seals leaking combustion gas into the bay, a fault well known on this engine by its nickname | Injectors removed, seats cleaned, new seals, coded. See Mercedes diesel injector replacement |
| OM651 and OM654 with AdBlue: 2015 on | AdBlue countdown, engine fault, no-restart warning | NOx sensor, AdBlue injector or pump, DPF not regenerating | Read, sensor or injector replaced, countdown cleared. See Mercedes AdBlue diagnostics and repair |
| OM642 3.0 V6 diesel: E, ML, GL, Sprinter, 2005 to 2018 | Loss of power, oil in the coolant or the V, limp mode | Swirl flaps, oil cooler seals in the V, turbo actuator | Flaps and seals replaced with the inlet off, actuator repaired or replaced. See swirl flap replacement |
| M271 1.8 Kompressor petrol: C-Class, E-Class, SLK, 2002 to 2011 | Rattle, rough running, timing fault | Timing chain and camshaft adjusters stretching | Chain, adjusters and tensioner as a set |
| M270 and M274 petrol: A, B, C-Class, GLA, 2012 on | Misfire, engine light, coolant loss | Ignition coils, plastic coolant parts, occasionally the chain | Coils tested individually, coolant parts replaced before they let go. See coolant leak repair cost |
| 7G-Tronic and 9G-Tronic automatics: most models 2004 on | Delayed engagement, harsh downshifts, gearbox message, stuck in a gear | Conductor plate, valve body, oil never changed | Oil and filter, conductor plate or valve body, adaptation reset. See Mercedes gearbox repair |
| All models: electrics | Random warnings, keyless faults, battery drain, wipers or lights with a mind of their own | A SAM module, corroded wiring or earths, water in a module, software | Traced on the network, module coded where replaced. See Mercedes ECU coding |
| E-Class, S-Class, GLE, GLS with Airmatic | Sitting low overnight, one corner down, suspension fault | Air strut leak, compressor, valve block or height sensor | Tested part by part before a compressor is blamed. See air suspension repair |
| EQA, EQB, EQC and the plug-in hybrids | Charging faults, range dropping, brake noise | Battery state of health, charge port, brakes corroding from light use | Read on the tool, brakes freed and serviced. See hybrid and EV repair |
Two of those are MOT matters as well as repairs: a lit engine management lamp is a major failure and a car sitting low on failed air suspension is a dangerous defect. The Mercedes diagnostics page covers how each warning is read, and the MOT page covers the test itself.
The one that brings owners to an independent
What is Mercedes coding, and why does a repair need it?
Mercedes coding is telling the car\'s control units that a new part has been fitted and what it is, and a repair needs it because a Mercedes will not accept an injector, a battery, a module, a key or a gearbox conductor plate that has not been coded to the car, so the part fits, the warning stays and the car runs badly, which is why a general garage that has replaced the right part sometimes sends the owner to a dealer to finish the job.
The coding is done here on manufacturer-level software as part of the repair, not as an extra: injectors coded with their correction values, batteries registered so the charging system knows the age, SAM and body modules programmed when they are replaced, and the gearbox adapted after a conductor plate. It is also how an ECU fault is told apart from the sensor that is feeding it bad data, which is the diagnosis most owners searching for ECU repair actually need.
See Mercedes ECU coding for what can and cannot be coded on your model, Mercedes diagnostics for how the read works, and auto electrician St Helens for the wiring side. Ring 01744 808586 with the registration and what has been fitted.
How a visit runs
What happens when your Mercedes comes to Boundary Road
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The car is looked up before it arrives
Model, engine code, mileage and the known points for that combination, so an OM651 at 90,000 miles or an E-Class with a gearbox message is on the sheet before the bonnet is up.
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Read on manufacturer-level software
Every module, not just the engine. Stored and pending codes, live data, the AdBlue and DPF counts, the coding history and the freeze-frame of when the fault happened.
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Inspected on the ramp
Chain noise listened for cold, injector seats checked for crust, oil condition checked for dilution, Airmatic height and leak tested, brakes and bushes measured.
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You get a phone call with the answer and a price
What it is, what it costs, and what can wait. Nothing is fitted on a guess and nothing extra is done without you saying yes.
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Repaired with parts to Mercedes specification
Genuine or OE-quality parts, the oil the engine is rated for, and everything that needs coding, from injectors to modules, done on the tool.
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Reset, recorded and road tested
Service indicator reset, the digital service book updated, and the car driven before it goes back.
The question we get asked most
Does using an independent Mercedes specialist affect my warranty?
Using an independent Mercedes specialist does not affect your warranty. UK Block Exemption rules mean Mercedes cannot tie the warranty to dealer servicing. Provided the work follows the Mercedes schedule, uses parts and oil to the correct specification and is properly recorded, the manufacturer warranty stays exactly as it was.
Those three conditions are how we do the job anyway. The schedule is read from the car, the oil carries the Mercedes approval for the engine, and the service goes into the digital service book, which is the record a dealer or a buyer checks. Keep the invoices; they list the oil and the parts.
What changes is the bill and the conversation. Dealer labour rates on these cars are among the highest in the trade, and a dealer will sell you a gearbox for a fault that turns out to be a conductor plate. Here the reading is explained, the part is proven before it is quoted, and the figure sits well below the franchise. A bigger job can go on Payment Assist, and it can be paired with the MOT so the car comes in once. See Mercedes servicing for the schedule detail and is a full service history worth it for what the record does at resale.
Every Mercedes job, one garage
The Mercedes work we do, page by page
Each of these goes deeper on one job: the faults, the method, the cost and the questions owners ask.
A and B Service
What each includes, to the Mercedes schedule, with the digital book updated. See Mercedes A Service and Mercedes B Service.
Mercedes diagnostics
Warnings, limp mode and faults read on manufacturer-level software. See Mercedes diagnostics.
ECU coding
Injectors, batteries, modules and keys coded to the car. See Mercedes ECU coding.
Timing chain and injectors
The OM651 chain and the injector seals. See timing chain replacement and injector replacement.
AdBlue and DPF
The countdown, the sensors and the filter. See AdBlue diagnostics and repair and Mercedes DPF cleaning.
Gearbox
7G-Tronic and 9G-Tronic oil, conductor plates and valve bodies. See Mercedes gearbox repair.
Mercedes specialist St Helens — paying over time
Mercedes repairs never arrive in a convenient month
Nobody plans for the chain rattle or the gearbox message. Whatever the diagnosis turns into can be spread across four months at nought per cent through pay monthly car repairs, decided on a soft search that does not mark your credit file.
The diesel that brings most Mercedes in
What goes wrong on the Mercedes OM651 diesel, and when should it be done?
The Mercedes OM651 diesel in the A, B, C and E-Class, the GLA, GLC, Vito and Sprinter has two known points: the timing chain, tensioner and guides, which wear and show as a rattle for a second or two on a cold start, and the injector seals, which leak combustion gas into the engine bay and show as a chuffing noise, a diesel smell and a black crust round the injector, and both are cheapest the week they start.
The chain is confirmed on the tool and by listening with the engine cold, and done as a set with the tensioner and guides, because a chain caught in time stays a chain job. The injector seals are dealt with by removing the injectors, cleaning the seats, fitting new seals and coding the injectors back to the car, and left alone the crust seizes the injector in the head, which turns a seals job into an extraction.
Both engines also carry the AdBlue and DPF systems that fail on short journeys, and the oil dilution that comes with them, so the read at every service covers all four. See Mercedes timing chain replacement, Mercedes diesel injector replacement and timing chain replacement cost. Ring 01744 808586 the first morning you hear either.
The schedule
What does Mercedes servicing need that other cars do not?
Mercedes servicing needs the A and B Service pattern followed rather than a generic interim and full, the oil to the exact Mercedes sheet approval the engine is rated for, every visit written into the digital service book, and on the diesels the AdBlue and DPF counts, the oil dilution and the injector seats read at every visit, because half the faults on a modern Mercedes start with an oil or a record that was treated as generic.
The A Service is the smaller one and the B Service the larger, alternating year by year, and the car tells you which is due; the B adds the filters, the brake fluid on its two-year cycle and the deeper inspection. Both are done here to the Mercedes list, not a menu, and the digital service book is updated on the tool so the record reads exactly as it would from a dealer.
The record matters at resale on a Mercedes more than most, because the digital book is what a buyer or a dealer checks. See Mercedes A Service and Mercedes B Service for what each includes, Mercedes servicing St Helens for the schedule detail, and what is included in a car service for how the tiers compare.
The numbers
Six numbers behind a Mercedes
The figures that decide what we look at first on your car.
Where the cars on our ramps come from
Mercedes specialist St Helens, and the towns owners drive in from
Boundary Road is a couple of minutes off the A58 and the Linkway, and minutes from junction 23 of the M6. Mercedes come from further than most of what we see, usually after a dealer quote for a gearbox, injectors or coding.
Cars also come over from Liverpool, Wigan, Warrington and across Cheshire. Mercedes servicing covers the routine work and Mercedes diagnostics the faults.
Worth knowing
Why a Mercedes gearbox fault is so often a £300 plate and not a £3,000 gearbox
The 7G-Tronic automatic in most Mercedes from 2004 on is controlled by a conductor plate inside the gearbox that carries the speed sensors and the electronics. When it fails, the gearbox loses a gear, holds a gear, engages late or throws a message, which looks exactly like a gearbox that has had it. It is a plate and an oil change, with the adaptation reset on the tool, and a dealer quote for a reconditioned gearbox for those symptoms is worth a second opinion every time.
The read on the tool tells the two apart in minutes, and it is why the gearbox conversation here starts with the plate and the oil rather than the gearbox.
The cars we see
A-Class, C-Class, E-Class, GLA, GLC, Sprinter: the Mercedes on our ramps
The C-Class and A-Class are the cars we see most, because there are more of them and because the OM651 diesel brings them in; the E-Class, GLA and GLC follow for the same engine, the gearbox and the electrics; and the Vito and Sprinter vans make up the rest of a typical month with the same diesel worked harder, plus the older E-Class and ML with the OM642 V6.
Each has its own pattern. The OM651 cars are chains, injector seals, AdBlue and oil dilution. The petrols are coils and coolant parts. The E-Class and GLE add Airmatic and the electrics, and the older V6 diesels are swirl flaps and oil cooler seals. Every one of them is the coding that a general garage cannot do.
The EQ electrics and the plug-in hybrids add battery state of health and software, and the manufacturer-level tool is what makes them workable outside a dealer. Whatever the badge on yours, Mercedes diagnostics covers the fault-finding side, Mercedes servicing the routine work, and the registration tells us the rest.
Been quoted by a Mercedes dealer and want a second figure?
Send the registration and the quote. We tell you whether the diagnosis stands up, what our price would be, and the next free slot. Gearbox, injector and AdBlue quotes in particular are worth a second look.
Mercedes specialist St Helens — get in touch
Tell us the model, the engine and what it is doing
A rattle on a cold start, a chuffing noise, an AdBlue countdown, a gearbox message or a service due. That tells us what to look at first, and the price follows the reading rather than the badge.
Fastlane Autocare, 232-254 Boundary Road, St Helens, WA10 2PZ. Open Monday to Friday 8:30am to 5:00pm and Saturday 9:00am to 12:30pm. Ring 01744 808586, use the contact page, or send the registration over and we will look the car up before you arrive.
Mercedes specialist St Helens • straight answers
Questions Mercedes owners ask us most
Fastlane Autocare is an independent Mercedes specialist on Boundary Road in St Helens, a couple of minutes off the A58 and the Linkway, servicing, diagnosing, coding and repairing every Mercedes from the A-Class to the Sprinter on manufacturer-level software at independent labour rates, with the digital service book updated as a dealer would.
Cars come in from across the borough, Widnes, Warrington, Wigan and Liverpool. See Mercedes servicing and Mercedes diagnostics, and the contact page for directions. Ring 01744 808586.
An independent Mercedes specialist does not void your warranty: under UK Block Exemption rules Mercedes cannot tie the warranty to dealer servicing, so provided the A and B Service schedule is followed, parts and oil meet the Mercedes specification and the work is recorded in the digital service book, the warranty stays intact.
That is how the job is done here, with the oil approval on the invoice and the book updated on the tool. See Mercedes servicing and why the record matters.
We code Mercedes parts and modules on manufacturer-level software as part of the repair: injectors with their correction values, batteries registered to the charging system, SAM and body modules programmed when replaced, keys, and the gearbox adapted after a conductor plate, which is the step a general garage cannot do and the reason a correctly replaced part sometimes still shows a warning.
See Mercedes ECU coding for what can be coded on your model and Mercedes diagnostics for the read. Ring 01744 808586 with what has been fitted.
A Mercedes that rattles for a second or two on a cold start very often has timing chain guides and a tensioner that are wearing, on the OM651 diesel and on several petrol engines, and it is worth acting on early because a chain caught in time stays a chain job, while a chain that jumps is an engine.
It is confirmed on the tool and by listening with the engine cold, not guessed. See Mercedes timing chain replacement and timing chain replacement cost. Ring 01744 808586 the first morning you hear it.
A chuffing noise and a diesel smell from a Mercedes OM651 engine, with a black crust building up round one injector, is the injector seal leaking combustion gas into the engine bay, a fault well known on this engine by its nickname, and it is dealt with by removing the injector, cleaning the seat, fitting a new seal and coding the injector back to the car.
Left alone, the crust seizes the injector in the head and a seals job becomes an extraction. See Mercedes diesel injector replacement and Mercedes servicing.
The Mercedes AdBlue warning means the emissions system has logged a fault or is running low, and on the OM651 and OM654 diesels it is a countdown: the car counts down the starts or the miles and refuses to restart once it reaches zero, and the cause is more often a NOx sensor, an AdBlue injector or the pump than the fluid level, which is why topping up rarely clears it.
The system is read, the failed part replaced and the countdown cleared. See Mercedes AdBlue diagnostics and repair and AdBlue faults. Ring 01744 808586 before the countdown gets low.
We will not delete the DPF or EGR on a Mercedes diesel, because removing or defeating either is illegal on a road-going vehicle in the UK and an automatic MOT failure, and what we do instead is find why the system is blocking and carry out a proper DPF clean or EGR valve replacement so the car runs cleanly and passes.
Short journeys are the usual cause. See Mercedes DPF cleaning and Mercedes EGR valve replacement.
We service the Mercedes 7G-Tronic and 9G-Tronic automatics with the correct-specification oil, the filter and the adaptation reset on the tool, and we diagnose the conductor plate and valve body before any gearbox is quoted, because a lost gear, a late engagement or a gearbox message on a 7G-Tronic is a plate far more often than a gearbox.
A dealer quote for a reconditioned gearbox for those symptoms is worth a second opinion. See Mercedes gearbox repair and gearbox repairs St Helens.
Swirl flaps on the Mercedes OM642 V6 diesel are small valves in the inlet manifold that improve mixing at low revs, and they fail by seizing or their linkages breaking, showing as a loss of power and a fault code, so they are replaced properly with the manifold off and the oil cooler seals in the V done at the same time, because the same strip-down reaches both.
A swirl flap fault on an OM642 is one to act on rather than leave. See swirl flap replacement and Mercedes turbo replacement for the actuator that fails alongside.
A Mercedes with random electrical faults, wipers or lights with a mind of their own, keyless that stops working or warnings that come and go, usually has a SAM module problem, corroded wiring or earths, water in a module from a blocked drain, or software that needs updating, and it is traced on the network with the manufacturer-level tool rather than by swapping modules.
A cluster of warnings after a flat battery is usually the battery. See Mercedes ECU coding and auto electrician St Helens. Ring 01744 808586.
A Mercedes A Service is the smaller service and the B Service the larger, alternating year by year with the car telling you which is due, and the B adds the filters, the brake fluid on its two-year cycle and the deeper inspection to the oil, filter and checks of the A, with both done here to the Mercedes list and written into the digital service book.
See Mercedes A Service and Mercedes B Service for exactly what each includes.
A Mercedes should be serviced every 12 months or at the mileage the car's service indicator counts down to, whichever comes first, alternating A and B Services, with the years figure applying to a car that has barely moved and the oil dilution counter on a short-journey diesel sometimes asking for an oil change earlier.
Brake fluid is on a two-year cycle with the B Service. See Mercedes servicing and what is included in a car service.
A Mercedes E-Class, S-Class, GLE or GLS that sits low overnight has an Airmatic leak or a tired compressor, and we fix it by testing the air struts, the lines, the valve block and the compressor individually so the part that has actually failed is replaced rather than the whole system.
The DVSA classes an inoperative air suspension system as a dangerous MOT defect. See air suspension repair and Mercedes suspension repair.
We read Mercedes fault codes on manufacturer-level diagnostic software that talks to every module on the car, not a generic code reader, so a warning is traced to the module that logged it with the live data and freeze-frame that explain why, and coding, adaptations, the digital service book and software updates are handled on the same tool.
That matters on a car where one failed sensor lights three warnings. See Mercedes diagnostics and the engine warning light.
We use genuine Mercedes parts where the job calls for them and OE-quality parts from the manufacturers who supply Mercedes where they are the same part in a different box, and either keeps the warranty because the specification, not the logo, is what the rules require.
Injectors, conductor plates and software-dependent modules are where the genuine part earns its price; pads, filters and bushes from the OE supplier do not. See Mercedes servicing and car repair cost.
We service and repair the Mercedes Vito and Sprinter as well as the cars, and the vans carry the same OM651 diesel worked harder: the chain, the injector seals, the AdBlue system and the DPF on urban work, plus clutches, dual-mass flywheels and suspension that carries a load every day, with the read and the repair turned round as quickly as the job allows.
A van off the road costs its owner every day. See van MOT and servicing St Helens and Mercedes DPF cleaning, or ring 01744 808586.
We work on the Mercedes EQA, EQB and EQC and the plug-in hybrids, reading battery state of health on the manufacturer-level tool, dealing with charging faults, servicing the engine and the parts an electric car still has, and freeing the brakes that corrode from light use because the car does most of its braking through the motor.
High-voltage work is inspection and diagnosis by qualified technicians. See hybrid and EV repair St Helens and MOT St Helens.
An independent Mercedes specialist is usually cheaper than the dealer, because the labour rate is lower and because the fault is proven before the part is quoted, which on a Mercedes is the difference between a conductor plate and a gearbox, or a sensor and an AdBlue pump, at the same parts specification and with the warranty intact.
Where a job is genuinely big, it can be spread. See pay monthly car repairs and car repair cost.
You can spread the cost of Mercedes repairs over three, four or six months at nought per cent with Payment Assist, decided on a soft search that does not mark your credit file, which matters on a car where a timing chain, a set of injectors or a gearbox plate is a real bill.
See pay monthly car repairs for how it works and timing chain replacement cost for the figures, or ring 01744 808586.
We cover Mercedes work for St Helens and the towns around it, including Haydock, Prescot, Rainhill, Newton-le-Willows, Billinge, Eccleston, Widnes, Warrington, Wigan and Liverpool, from the workshop on Boundary Road, because chain, injector, gearbox and coding work need the ramp and the manufacturer tool.
Owners come from across Cheshire and Lancashire after a dealer quote. See the contact page for directions and garage services in St Helens for everything else done here.