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OBD injector module relay fault guide

P0612 Code Meaning UK

P0612 means “Fuel Injector Control Module Relay Control”. In plain English, the ECU, PCM or fuel injector control module has detected a problem with the relay control circuit that helps power or activate the injector control system. This can cause hard starting, no-start, misfires, cutting out, limp mode, rough running, smoke or injector control problems.

📅 Updated June 2026 🇬🇧 UK diagnostic guide 🛠 Injector relay control advice
Quick answer Diagnosis steps Fault Codes Hub
✓ Relay control fault explained ✓ UK repair cost guide ✓ Fuse and wiring checks included ✓ Links back to indexed fault-code hub
Quick answer Meaning Symptoms Causes Can you drive? Repair costs Diagnosis Common mistakes MOT impact Used car advice Related guides FAQs
Quick answer

What does P0612 mean?

P0612 means the ECU, PCM or fuel injector control module has detected a fault with the fuel injector control module relay control circuit. In simple terms, the module is unhappy with the relay or power-control circuit used to switch the injector control system on and off.

This can be caused by a bad relay, blown fuse, corroded fusebox terminal, broken wire, poor earth, weak battery, charging fault, water ingress, connector problem, failed injector control module or ECU/PCM control issue.

P0612 should be diagnosed carefully because injector control relies on stable power. If the relay circuit fails completely, the car may crank but not start, cut out, misfire or run badly.

Most important first check

Check injector control module relay operation, fuses, power feeds, earths and battery voltage.

Main risk

The car may misfire, smoke, enter limp mode, cut out or refuse to start.

Best next step

Scan all modules, record related injector codes and test the relay circuit properly.

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Code meaning

P0612 — Fuel Injector Control Module Relay Control

The fuel injector control system needs a reliable power supply. On some vehicles, a relay is used to provide or control power to the injector control module or injector control circuit. The ECU or PCM monitors this relay control circuit to make sure it behaves correctly.

When P0612 appears, the control module has detected that the relay control circuit is not performing as expected. The relay may not be switching, the control wire may be open or shorted, the fusebox may be corroded, or the module may not be receiving the correct power supply.

Because injector control affects combustion directly, a relay control problem can lead to no-start symptoms, rough running, misfires, poor emissions, smoke and limp mode.

Mechanic view

Why P0612 needs careful fault finding

P0612 should not be treated as an automatic injector control module replacement code. A relay or fusebox fault can look serious but may be cheaper to repair than a module.

If the vehicle has been jump-started, had a flat battery, water leak, fusebox corrosion, injector work, ECU work or previous no-start symptoms, those clues matter. Injector control circuits are sensitive to poor voltage and bad connections.

This is why P0612 links closely with P0611 fuel injector control module performance, P0201 injector circuit fault, P0300 random/multiple misfire, P0562 system voltage low, P0610 vehicle options error and the main OBD fault codes hub.

Symptoms

Common symptoms of a P0612 code

Symptoms depend on whether the problem is caused by the relay, fuse, wiring, battery voltage, earth connection, injector control module or ECU/PCM control circuit.

Engine management light

A warning light may appear when the ECU detects a relay control fault.

Hard starting

The car may crank longer than normal if injector control power is unstable.

No-start condition

If the relay circuit fails completely, the engine may crank but not start.

Cutting out

An intermittent relay or power feed can cause sudden stalling.

Rough idle

Poor injector control power can cause uneven running or shaking at idle.

Misfires

The engine may misfire if injector control power drops out or becomes unstable.

Limp mode

The vehicle may reduce power to protect the engine and fuel system.

Smoke from exhaust

Poor injector control can cause poor combustion and visible smoke.

Multiple fault codes

Injector, voltage, communication, relay or misfire codes may appear alongside P0612.

Common causes

What causes P0612?

P0612 is usually linked to relay control, power supply, wiring or module control problems.

Relay

Faulty injector control relay

A worn, sticking or failed relay can stop the injector control system powering up correctly.

Fuse

Blown fuse or poor fuse contact

A blown fuse or heat-damaged fusebox terminal can interrupt injector module power.

Wiring

Relay control wiring fault

Open circuits, shorts to ground, shorts to power or broken wires can trigger P0612.

Connector

Corroded connector

Moisture, loose pins or corrosion at relay, fusebox or module connectors can create intermittent faults.

Voltage

Low battery voltage

Weak battery voltage can prevent relays and modules from switching correctly.

Charging

Alternator charging fault

Unstable charging voltage can cause relay and module control issues.

Earth

Poor earth connection

Bad grounds can stop the relay control circuit or module from operating properly.

Water

Water ingress

Water in the fusebox, scuttle area, ECU area or connectors can cause relay control faults.

Module

Injector control module fault

The module may fail internally, especially if relay, fuse, wiring and voltage checks all pass.

Safe to drive?

Can you drive with P0612?

Driving with P0612 depends on how the car behaves. If the engine starts normally, idles smoothly, has no smoke, no limp mode and no obvious misfire, a short journey to a garage may be possible.

Avoid normal driving if the vehicle is hard to start, cuts out, misfires, smokes heavily, smells of fuel, enters limp mode or refuses to start. A relay control fault can cause injector control to drop out unexpectedly.

✅ Lower risk: warning light only, normal starting, smooth idle and no smoke.

⚠️ Medium risk: intermittent starting, occasional hesitation, stored injector or relay codes.

🚫 Higher risk: no-start, cutting out, misfire, heavy smoke, fuel smell, limp mode or flashing engine light.

Can You Drive With Engine Light? Car Won’t Start Diagnosis
Relay warning

Do not ignore intermittent no-start faults

A failing relay or poor fusebox connection can work one moment and fail the next. This is why some P0612 vehicles start normally sometimes, then suddenly crank without starting.

If P0612 appears with P0611 injector control module performance, P0201 injector circuit fault or P0562 system voltage low, the relay, voltage supply and injector control wiring should be checked first.

If the vehicle has recently had a flat battery, jump start, alternator fault or water leak, mention this to the technician because it can change the diagnostic direction.

P0611 Injector Module P0562 Voltage Low Battery Warning Light
UK repair costs

Typical UK repair costs for P0612

Costs vary because P0612 may be caused by a cheap relay or fuse issue, a wiring problem, fusebox corrosion or a more expensive module fault.

Diagnostic scan and relay testing

Typical range: £60–£150.

Relay replacement

Typical range: £20–£120+ depending on relay type and access.

Fuse or fusebox terminal repair

Typical range: £50–£250+.

Wiring or connector repair

Typical range: £80–£350+.

Battery and charging checks

Typical range: £40–£120, more if parts are required.

Earth strap repair

Typical range: £60–£220+.

Water damage or fusebox repair

Typical range: £120–£600+.

Injector control module testing

Typical range: £120–£350+.

Injector control module replacement

Typical range: £300–£1,200+ depending on vehicle, coding and availability.

Repair Costs Guide UK OBD Fault Codes Hub
Diagnosis flow

How to diagnose P0612 properly

A good diagnosis should prove whether the relay control circuit is working. The relay, fuse, power feed, ground, control wire and injector control module supply should be checked before replacing expensive modules.

✅ Scan all vehicle modules, not only the engine ECU.

✅ Record all injector, relay, voltage and communication codes.

✅ Check whether P0612 returns immediately after clearing.

✅ Check battery voltage and alternator charging voltage.

✅ Locate the injector control module relay and related fuses.

✅ Check whether the relay clicks and switches correctly.

✅ Test relay power supply, ground and control signal.

✅ Inspect relay terminals for heat damage or corrosion.

✅ Inspect fusebox terminals for water ingress or burning.

✅ Check injector control module power feeds with ignition on and during cranking.

✅ Inspect wiring between ECU/PCM, relay and injector control module.

✅ Check earth straps and module grounds.

✅ Check related codes such as P0611, P0201, P0300 and P0562.

✅ Confirm module failure only after relay, fuse, wiring and voltage checks pass.

Real experience

What I would check first

On a real P0612 fault, I would not start by ordering an injector control module. I would first check the relay, fuse, battery voltage, fusebox condition, power feeds and grounds.

If the vehicle is a no-start, I would check whether the injector control system is receiving power during cranking. If the power disappears or the relay does not switch, the problem may be in the relay control side rather than the module itself.

Only after proving the relay circuit, wiring, voltage and earths are good would I suspect a failed injector control module or ECU/PCM control problem.

P0611 Injector Module P0201 Injector Circuit Diagnostic App
Common mistakes

Mistakes to avoid with P0612

P0612 can become expensive if simple relay and power supply checks are skipped.

Replacing the module too quickly

A relay, fuse, fusebox or wiring fault can make a good module look faulty.

Ignoring fusebox corrosion

Water and heat damage around relay terminals can cause intermittent no-start faults.

Ignoring low voltage

Weak battery or charging faults can stop relays and modules operating correctly.

Only scanning one module

Other modules may store voltage, communication or immobiliser clues.

Clearing the code without recording it

Freeze-frame and related codes can show when and why the relay control problem happened.

Ignoring intermittent faults

A relay may work during testing but fail when hot, wet or under vibration.

MOT impact

Will P0612 fail an MOT?

P0612 itself is not usually the direct MOT failure item. The MOT concern is what the fault causes. If it causes an engine warning light, no-start issue, rough running, misfire, smoke, poor emissions, fuel smell, limp mode or unsafe behaviour, it can become an MOT issue.

If the car is smoking, misfiring, cutting out or difficult to start, it is better to diagnose and repair the relay control problem before the MOT. Injector control faults can affect emissions and drivability.

⚠️ Higher risk: no-start, cutting out, flashing engine light, misfire, smoke, fuel smell or limp mode.

⚠️ Medium risk: intermittent starting, stored injector codes, relay codes or voltage codes.

✅ Lower risk: fault repaired, no warning light, smooth idle and normal starting.

Engine Light MOT Guide Common MOT Failures
Emissions and relay control

Why injector power faults can affect emissions

Injector control depends on stable electrical power. If the relay circuit is unstable, fuel delivery may be inconsistent. That can cause rough running, smoke, high emissions and catalyst or DPF stress.

A vehicle with active injector control relay problems may still run, but that does not mean it is safe to ignore before an MOT or long journey.

Engine Management Light Guide Fault Codes Hub
Used car buying advice

P0612 on a car you want to buy

If a used car has P0612 stored, be careful. A relay fault may be simple, but repeated relay control faults can also point to fusebox corrosion, water ingress, wiring damage, voltage problems or injector control module issues.

Before buying, check whether the engine starts cleanly from cold and hot, whether it cuts out, whether there are injector or voltage codes, and whether the fusebox or relay area shows signs of water damage or previous repair.

✅ Ask for a full diagnostic report, not just a cleared code.

✅ Check for injector, relay, voltage and communication codes.

✅ Check whether the vehicle has had water ingress or fusebox repair.

✅ Avoid cars with no-start history unless the fault is diagnosed properly.

✅ Budget carefully if wiring, fusebox or module testing is needed.

Used Car Buying Guides Inspection Checklist
Negotiation warning

Do not ignore relay control faults

Relay control faults can leave a vehicle stranded if they become intermittent. A car that starts normally during viewing may still have a heat, vibration or moisture-related relay fault.

If the fault is already diagnosed as a simple relay replacement, it may be a small repair. But if the fault is active, repeated, unexplained or linked with water damage, poor starting or cutting out, proceed carefully.

Buying With Advisories Check MOT History
Frequently asked questions

FAQs about P0612

Common questions about P0612 fuel injector control module relay control, safe driving, repair costs, relay faults and MOT impact.

What does code P0612 mean?

P0612 means the ECU, PCM or fuel injector control module has detected a problem with the injector control module relay control circuit.

Is P0612 serious?

It can be serious if it causes hard starting, no-start symptoms, cutting out, misfires, smoke or limp mode.

Can I drive with P0612?

Short driving may be possible if the engine runs normally, but avoid driving if it cuts out, misfires, smokes, refuses to start or enters limp mode.

Does P0612 always mean the injector control module is faulty?

No. The relay, fuse, fusebox, wiring, connectors, earths, battery voltage and charging system should be checked first.

Can a bad relay cause P0612?

Yes. A faulty injector control module relay or relay control circuit problem is one of the main causes of P0612.

Can low voltage cause P0612?

Yes. Low battery voltage or poor charging voltage can stop relays and modules operating correctly.

Will P0612 fail an MOT?

P0612 can affect an MOT if it causes warning lights, no-start issues, smoke, poor emissions, misfires or unsafe behaviour.

Should I replace the relay first?

The relay should be tested first. If it fails testing, replacement may be sensible, but wiring, fuses and control signals should also be checked.

Can P0612 be cleared?

It may clear temporarily, but if the relay control fault remains, the code will return. Repeated P0612 needs proper diagnosis.

How much does P0612 cost to fix in the UK?

Diagnosis may cost around £60–£150. Relay or fuse repairs may be cheaper, while wiring, fusebox or module faults can cost much more.

About this guide

Written for practical UK fault finding

Motor Vehicle Expert explains diagnostic trouble codes in clear, mechanic-style language for UK drivers. This P0612 guide is designed to help you understand fuel injector control module relay control faults, likely causes, safe driving advice, repair costs, MOT risks and used-car buying concerns before replacing expensive parts.

Fault codes should always be treated as a diagnostic starting point. P0612 can involve relays, fuses, fusebox terminals, wiring, earth straps, battery voltage, charging faults, water ingress, ECU control and injector control module power supply. Proper testing is better than guessing.

For the full fault-code library, always start with the indexed OBD Fault Codes Explained UK hub.