Car Immobiliser Diagnostics and Repair On Site, Same Day in Devon, Dorset and Somerset
Dean of DB Car Keys, the mobile auto locksmith from Honiton, diagnoses and repairs car immobiliser faults on site across Devon, Dorset and Somerset, arrives in 20 to 60 minutes and reads the fault codes in 15 to 20 minutes.
Most immobiliser faults are electronic and not mechanical. The fault codes are read first, the key is paired to the car again in 30 to 45 minutes in most cases, and the car is not towed. The price is quoted by phone before travel, with no call out fee.
Engine cranks and does not start? Call the locksmith
Immobiliser work is quoted by phone before travel. Dean confirms the likely fault and the price on the call.
Dean has worked as a mobile auto locksmith since 2009 and is fully insured and DBS checked. 66 Google reviews rate DB Car Keys 5 stars, and the price is given before Dean travels.
Car Immobiliser Repair Cost and Price Factors
Car immobiliser repair cost depends on the fault, and DB Car Keys quotes the price by phone before travel, with no call out fee. The table gives the price of the four immobiliser repair jobs and of the three jobs that sit closest to them.
| Immobiliser job | Price | What the price covers |
|---|---|---|
| Key and ECU synchronised again after a flat battery or battery work | £60 to £120 | The existing key is paired to the car again through the diagnostic port, in 30 to 45 minutes, with no parts. |
| Key pairing to a replacement ECU | Quoted by phone from the make | Every key is paired to the new unit, in 45 to 90 minutes. |
| New key for a failed transponder chip | £100 to £280 | A transponder key cut and programmed to the existing ECU, in 30 to 45 minutes. |
| ECU immobiliser module fault | Quoted after the diagnosis | The fault is explained before any work starts. The fix and the cost vary by make. |
| Lost car keys, every key missing | £150 to £400 or more | A new key programmed from the VIN, with no original. |
| Spare car key at the same visit | £80 to £220 | A second key cut and programmed while the equipment is connected. |
| Key fob repair and replacement, remote buttons dead | £40 to £100 for a repair | The remote part of the key, which works the locks and not the engine. |
The work uses the equipment for programming car keys, so the diagnosis and the repair happen in one visit. Three factors set the price of an immobiliser repair.
Dean states the fault, the fix and the cost before the work starts, with no call out fee. Workmanship carries a 30 day guarantee, and payment is taken on completion by cash, by bank transfer or by card where card payment is available.
Four Symptoms of a Car Immobiliser Fault
A car immobiliser fault shows four common symptoms, an engine that cranks and does not fire, a red padlock warning light, a key that is no longer recognised and all keys failing at once. The vehicle immobiliser is a mandatory anti theft system in all UK cars made from 1998 onwards, and it stops the engine starting without the correct key signal. A faulty immobiliser, or a key that has lost its pairing, leaves an engine that turns over and never starts, with no mechanical noise and no fuel smell.
Immobiliser problems are usually electronic and not mechanical. The car is not broken, and the ECU is doing its job by blocking the engine, because it does not recognise the transponder signal of the key. In many cases the fix is a synchronisation or a key pairing procedure, done with the same equipment as programming car keys, and not a parts replacement.
The Engine Cranks and Does Not Fire
The starter motor works and the engine turns over, and combustion never happens. The fuel supply or the ignition is blocked. This is the classic immobiliser symptom.
A Red Padlock Warning Light
A red padlock, a key outline or a car with a key symbol on the dashboard shows that the ECU has detected an immobiliser fault or does not authenticate the key signal.
The Key Is No Longer Recognised
A key that started the car yesterday does not work today. The fault often follows a flat battery, a battery replacement or a power interruption during a service.
All Keys Fail at the Same Time
All registered keys stop working at once. The fault points to the ECU and not to the keys, because several keys rarely fail together.
📍 Real call out, Exeter, Devon
"A Toyota Prius owner in Exeter called us after the 12 volt auxiliary battery went completely flat. After a jump start the car turned over fine and the engine did not fire, and the immobiliser warning light was lit. Hybrid vehicles have a specific synchronisation requirement after a 12 volt power loss that differs from standard petrol cars. Our diagnostic software covers the procedure for the Prius, and the car was back in use within 40 minutes of our arrival."
📍 Real call out, Sherborne, Dorset
"A BMW 3 Series owner in Sherborne had his ECU replaced by an independent garage after a fault. Afterwards, none of his three keys would start the car. The replacement ECU had no key data registered to it, because the garage had not performed the key pairing procedure after fitting the new unit. We attended his home, connected our programming software, and paired all three keys to the replacement ECU. Two hours from first call to driving away."
📍 Real call out, Plymouth, Devon
"Ford PATS (Passive Anti Theft System) faults are the most common immobiliser call out we see around Plymouth and Exeter. A Ford Focus owner called us after her car developed an intermittent no start issue. It would start fine some days and then refuse completely on others. Our equipment read a stored PATS fault code. The transponder in the key head had developed an intermittent connection, which is common on older flip key housings. A new key head programmed to the existing ECU resolved the issue completely."
⏱ Eight times an immobiliser fault appears
Six Checks That Point to an Immobiliser Fault
Six checks point to an immobiliser fault or away from one, and each check takes a minute at the car. The table gives each check with what it shows and the next step. A driver who wants to fix a car immobiliser at home starts with the first check.
| Check | What the check shows | Next step |
|---|---|---|
| Try the spare key | The spare starts the car, so the transponder chip in the first key has failed. | A new key is cut and programmed to the existing ECU. |
| Look for the immobiliser warning light | A red padlock or a car with a key symbol stays on or flashes while the engine cranks. | An immobiliser fault is likely, and the fault codes confirm it. |
| Think back to the last battery work | The fault appeared straight after a flat battery, a jump start or a battery replacement. | The key and the ECU are synchronised again, in 30 to 45 minutes. |
| Check whether the ECU was replaced | No key starts the car after a garage fitted a new ECU. | Every key is paired to the new unit, in 45 to 90 minutes. |
| Count the keys that fail | All keys stopped working at the same time. | The fault points to the ECU, and the fault codes are read before any quote. |
| Check for no light and no recent work | No warning light shows, and no battery or ECU work was done. | A fuel pump failure or a crankshaft sensor fault causes the same symptom, which is a job for a garage. |
One call with the make, the model, the year and the symptom gets a likely fault and a price, across Devon, Dorset and Somerset.
Six Immobiliser Fault Types Diagnosed and Repaired
The six immobiliser fault types are diagnosed from the fault codes, and the exact cause is named before any repair starts.
Key and ECU Synchronisation
The most frequent immobiliser fault is a key and an ECU that have lost their pairing. The fault often follows a flat battery, a battery replacement, a power interruption or a service with the battery disconnected. The key is fine and the ECU is fine, and the two have lost communication. A synchronisation procedure through the diagnostic port restores the pairing with no parts.
Key Pairing After an ECU Replacement
A replacement ECU holds no memory of any key, so all keys registered before lose their pairing. Every key is paired to the new unit through the diagnostic port. A garage with no specialist equipment does not perform this step, which is why many vehicles stay stranded after straightforward ECU work.
Failed or Intermittent Transponder Chip
The transponder chip in the key head fails from physical damage, water, extreme heat or age. An intermittent chip gives an unreliable no start fault, with a car that starts on some days and refuses on others. The fault codes identify a transponder chip issue, and the fix is a new key head programmed to the existing ECU.
ECU Immobiliser Module Fault
The immobiliser module of the ECU develops a fault of its own in some cases, on higher mileage vehicles most of all. The fault is less common than a key or a pairing issue. The diagnostics separate a module fault from a pairing issue, which matters because the fix and the cost are very different. The finding is explained before any work starts.
Power Loss and the Immobiliser Memory Reset
Some models are sensitive to power loss, Ford, Vauxhall and Peugeot most of all. A completely flat battery or a jump start makes the immobiliser module lose one or more key registrations. The key worked before the battery fault, and then one key or all keys are not recognised. The fix is a pairing or a registration procedure, and the key and the ECU hardware are sound.
Immobiliser Systems of Each Make
Each manufacturer uses its own immobiliser architecture, Ford PATS, VW and Audi Immo3 and Immo4, BMW EWS, CAS and FEM, and the Vauxhall system in the BCM. Each takes its own diagnostic software and procedures. The equipment carries software for the major makes on UK roads, to read fault codes, synchronise and pair keys across virtually all common systems.
Immobiliser Diagnostics in Four Steps
Immobiliser diagnostics runs in four steps at the car, and the exact fault is named before any quote.
The Call
Describe the symptoms, an engine that cranks and does not start, a warning light or a key that is not recognised. Dean asks a few diagnostic questions and gives an arrival time.
The Fault Code Scan
The diagnostic equipment is connected to the diagnostic port of the vehicle. A full immobiliser fault code scan shows what the ECU reports before any work starts.
The Diagnosis
Dean states the fault, the fix and the cost before the work starts, with no hidden charges. Most common faults are resolved in the same visit.
The Repair and the Test
The key is synchronised or paired again. The engine start is tested and every key is checked before Dean leaves, with no towing and no waiting.
Immobiliser Repair Times at the Vehicle
Immobiliser Systems by Vehicle Make
Immobiliser systems differ by vehicle make, and the diagnostic software covers the six system families on these cards.
Ford
PATS, Passive Anti Theft System
Ford PATS is the most common immobiliser fault across Devon and Somerset. The system reads the key chip through a transponder ring around the ignition barrel. PATS faults range from the loss of a single key to a full system reset. The PATS fault codes are read, and keys are registered and synchronised again across the Ford range.
VW, Audi, Seat and Skoda
Immo3 and Immo4
The VW Group uses Immo3 on older vehicles and Immo4 on models made after 2009. Immo4 is significantly more complex and takes specific software for key pairing. All four VW Group makes share the same architecture, which makes them one of the most common ECU pairing call outs across Plymouth and Exeter.
Call 07830249408 to confirm the modelBMW
EWS2, EWS3, CAS and FEM
BMW has used several immobiliser generations, EWS on vehicles before 2005, CAS (Car Access System) on models from 2005 to 2018 and FEM or BDC on models after 2015. The BMW software covers key pairing after ECU work, synchronisation after battery faults and new keys after lost keys.
Call 07830249408 for BMW immobiliser helpVauxhall and Opel
BCM immobiliser
Vauxhall builds the immobiliser into the BCM (Body Control Module). Key pairing takes dealer level software, which the equipment carries. Vauxhall Astra and Corsa immobiliser faults after battery work are particularly common in the area, and most are resolved on site.
Peugeot and Citroën
BSI, Built in Systems Interface
French vehicles manage the immobiliser and the body electronics through the BSI module. BSI faults are common after battery work and stop every key being recognised. The work covers BSI initialisation, key pairing and fault code clearing across the Peugeot and Citroën range.
Toyota and Lexus, hybrids included
Standard and Smart Entry systems
Toyota hybrids, the Prius most of all around Exeter, have a specific synchronisation requirement for the 12 volt auxiliary battery after a power loss. The procedure differs from a standard petrol vehicle and is a common source of confusion. The software for Toyota hybrids performs the correct synchronisation.
Recent Immobiliser Diagnostic Callouts
Six recent immobiliser diagnostic callouts across Devon, Dorset and Somerset, each with its time.
Toyota Prius, 12 volt battery loss, immobiliser synchronised again
BMW 3 Series, ECU replaced by a garage, all keys paired again
Ford Focus, PATS fault after battery work, key registered again
Vauxhall Astra, BCM synchronised after a flat battery, both keys checked
Peugeot 308, BSI fault cleared, key paired to the module
VW Transporter T6, Immo4 fault, key registration completed
The list of immobiliser repairs is updated regularly. Call 07830249408 with the symptoms for an arrival time.
Dean, DB Car Keys
Mobile Auto Locksmith and Immobiliser Specialist, Honiton, Devon
Dean is the car locksmith who answers the phone, reads the fault codes and does the repair. Dean is fully insured and DBS checked, and has diagnosed immobiliser faults across Devon, Dorset and Somerset for over 15 years.
Dean on Immobiliser Fault Jobs
Three points on immobiliser fault jobs in the first person, as Dean and DB Car Keys state them.
On the diagnosis
“We tell you exactly what the fault is, what is needed to fix it, and the cost, before we start. No hidden charges. Most common faults are resolved in the same visit.”
On an ECU replaced by a garage
“When an ECU is replaced, the new unit has no key data. Every key that was registered to the old ECU needs to be paired to the replacement unit. We perform full key pairing to replacement ECUs for most major makes including Ford, BMW, VW Group, Vauxhall and Peugeot.”
On towing
“In the vast majority of cases we fix the fault at your location, at home, at the workplace, in a car park or at the roadside. Towing is only necessary if the fault turns out to be a hardware ECU failure requiring a physical replacement, which is uncommon. We always confirm the situation by phone before travelling so there are no surprises.”
What DB Car Keys Customers Say
Verified Google reviews from immobiliser and car key customers across Devon, Dorset and Somerset.
Vehicle Makes Covered for Immobiliser Diagnostics
The diagnostic software covers the immobiliser systems of all major makes.
Call 07830249408 with the registration, and Dean confirms the job before travel.
Immobiliser Diagnostics Areas in Three Counties
On site immobiliser diagnostics reaches every area of Devon, Dorset and Somerset.
EX, PL and TQ postcodes, with Exeter, Plymouth and all Devon towns.
DT postcodes, with Bridport, Weymouth, Dorchester and the coastal towns.
TA and BA postcodes, with Taunton, Yeovil and rural Somerset.
Call 07830249408 for immobiliser diagnostics in EX, PL, TQ, DT, TA and BA postcodes.
Immobiliser Diagnostics FAQs
Sixteen common questions about immobiliser faults and immobiliser diagnostics, with the answers.