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OBD alternative fuel module memory fault guide

P0618 Code Meaning UK

P0618 means “Alternative Fuel Control Module Keep Alive Memory Error”. In plain English, the alternative fuel control module has a problem retaining its stored memory, learned values or configuration data. This can happen from low battery voltage, loss of permanent power feed, poor earths, blown fuses, wiring faults, connector corrosion, software issues or an internal module memory fault.

📅 Updated June 2026 🇬🇧 UK diagnostic guide 🛠 Alternative fuel KAM fault advice
Quick answer Diagnosis steps Fault Codes Hub
✓ KAM memory fault explained ✓ UK repair cost guide ✓ Power feed 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 P0618 mean?

P0618 means the alternative fuel control module has detected a Keep Alive Memory error. Keep Alive Memory, often shortened to KAM, is the memory a control module uses to retain learned values, settings and configuration information even when the ignition is switched off.

On vehicles with alternative fuel systems, this may relate to LPG, CNG, flex-fuel, hybrid-supporting fuel control or manufacturer-specific fuel system modules. The exact system depends on the vehicle, but the fault points towards the module’s memory, power supply or ability to retain stored data.

In mechanic terms, do not jump straight to replacing the module. First check permanent battery feed, ignition feed, fuses, relays, earths, battery voltage, charging voltage, connector condition, water ingress and whether the battery has recently gone flat or been disconnected.

Most important first check

Check permanent power feed, ignition feed, module earths, fuses and battery voltage before blaming the module.

Main risk

The alternative fuel system may lose learned data, switch fuel modes badly, run poorly or enter limp mode.

Best next step

Scan all modules and check voltage, power supply and related memory codes properly.

Back to Fault Codes Hub Use Diagnostic App
Code meaning

P0618 — Alternative Fuel Control Module KAM Error

Control modules need memory to remember learned values. This may include fuel trims, adaptation values, switching strategy, configuration, calibration data and fault history. KAM allows the module to keep that information when the ignition is turned off.

When P0618 appears, the alternative fuel control module has detected that its stored memory is not being retained or read correctly. That can happen because the module has lost its permanent power supply, the battery voltage has dropped too low, the module ground is poor, the software has a fault or the memory inside the module has failed.

This is similar in principle to other memory-type control module faults, but it is focused on the alternative fuel control module rather than the main engine ECU.

Mechanic view

Why P0618 needs proper electrical checks

A KAM error often looks like a module fault, but in the workshop I would first prove the module has a clean permanent live, good ignition feed and solid earth. If the permanent feed drops out overnight, the module can forget its learned data and store P0618.

If the customer says the battery went flat, the car was jump-started, a battery was replaced, fuses were removed, water got into the fusebox or the car has been standing, that history matters.

This is why P0618 links closely with P0603 keep alive memory error, P0607 control module performance, P0562 system voltage low, battery warning light meaning, alternator not charging battery signs and the main OBD fault codes hub.

Symptoms

Common symptoms of a P0618 code

Symptoms depend on the vehicle and the alternative fuel system fitted. Some vehicles may show only a warning light, while others may have running, starting or fuel switching problems.

Engine management light

The engine warning light may appear if the module reports a memory or configuration fault.

Alternative fuel warning

Some vehicles may show a fuel system, LPG, CNG or manufacturer-specific fuel warning.

Poor fuel switching

The vehicle may not switch smoothly between petrol and alternative fuel modes.

Rough idle

Lost learned values can cause rough idle or unstable running after start-up.

Hard starting

The car may take longer to start if fuel system adaptation data is not retained.

Limp mode

The vehicle may reduce power if the module cannot trust its stored configuration.

Higher fuel use

Fuel economy may suffer if learned fuel data or switching strategy is lost.

Code returns after clearing

If the module keeps losing memory, P0618 may return after the next drive or key cycle.

Related voltage codes

Low-voltage, charging or module performance codes may appear alongside P0618.

Common causes

What causes P0618?

P0618 is usually caused by a module memory issue, but battery, voltage and power supply faults should be checked first.

Battery

Weak or flat battery

Low battery voltage can cause modules to lose memory or store KAM-related faults.

Power

Lost permanent power feed

If the module loses its constant battery feed, it may not retain memory after ignition off.

Fuse

Blown fuse or poor fuse contact

A fuse or fusebox terminal problem can interrupt module memory power supply.

Earth

Poor earth connection

Bad module grounds can cause unstable operation and memory faults.

Charging

Alternator charging fault

Overcharging or undercharging can upset control module memory and operation.

Wiring

Damaged wiring

Broken wires, high resistance or rubbed looms can affect module power and memory retention.

Water

Water ingress

Moisture in connectors, fuseboxes or module areas can cause memory and communication faults.

Software

Software or calibration issue

Incorrect coding, failed programming or corrupted software can trigger KAM-related errors.

Module

Internal module memory fault

The alternative fuel control module may have an internal memory fault if power and earth checks pass.

Safe to drive?

Can you drive with P0618?

Driving with P0618 depends on how the vehicle behaves. If it starts normally, runs smoothly, switches fuel modes correctly and has no limp mode, a short journey to a garage may be possible.

Avoid normal driving if the engine runs badly, stalls, cuts out, refuses alternative fuel mode, smells of fuel, shows multiple warnings or enters limp mode. Alternative fuel faults should be treated carefully because incorrect fuel control can affect emissions and drivability.

✅ Lower risk: warning light only, normal starting, smooth running and normal fuel switching.

⚠️ Medium risk: rough idle, poor fuel switching, stored voltage codes or recent flat battery.

🚫 Higher risk: limp mode, stalling, fuel smell, no-start, poor running or repeated memory loss after clearing.

Can You Drive With Engine Light? Use Diagnostic App
Mechanic warning

Do not ignore repeated memory loss

If P0618 returns after clearing, especially after the vehicle has been parked overnight, suspect loss of permanent power feed, poor earth or internal module memory failure.

If P0618 appears with P0562 system voltage low or P0603 keep alive memory error, start with battery, charging and power supply testing before replacing the module.

If the battery has recently gone flat or the vehicle has been jump-started, mention this during diagnosis because it may explain the memory fault.

P0603 KAM Error P0562 Voltage Low Battery Warning Light
UK repair costs

Typical UK repair costs for P0618

Costs vary because P0618 may be caused by a weak battery, poor fuse contact, power feed fault, earth fault, software issue or alternative fuel control module failure.

Diagnostic scan and power feed test

Typical range: £60–£150.

Battery testing or replacement

Testing may cost £40–£120. Replacement often costs £90–£250+.

Fuse or fusebox terminal repair

Typical range: £50–£300+.

Earth strap or ground repair

Typical range: £60–£220+.

Wiring or connector repair

Typical range: £80–£450+.

Alternator charging repair

Typical range: £120–£500+ depending on fault and vehicle.

Software update or coding

Typical range: £80–£300+.

Alternative fuel module testing

Typical range: £120–£350+.

Alternative fuel module replacement

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

Repair Costs Guide UK OBD Fault Codes Hub
Diagnosis flow

How to diagnose P0618 properly

A good diagnosis should prove whether the module is losing memory because of a power supply problem or because the module memory itself has failed. The basics matter: permanent live, ignition live, earth, fuses, voltage and connectors.

✅ Scan all vehicle modules and record related codes.

✅ Check whether P0618 returns immediately after clearing.

✅ Check if the code returns after the car is parked overnight.

✅ Ask whether the battery went flat, was disconnected or the vehicle was jump-started.

✅ Check battery voltage at rest and during cranking.

✅ Check alternator charging voltage at idle and under load.

✅ Check permanent battery feed to the alternative fuel control module.

✅ Check ignition feed to the module.

✅ Check module earths and voltage drop on grounds.

✅ Check related fuses, relays and fusebox terminals.

✅ Inspect connectors for corrosion, water ingress or loose pins.

✅ Check wiring for breaks, high resistance or poor previous repairs.

✅ Check software, coding and calibration where relevant.

✅ Confirm internal module memory failure only after power and earth checks pass.

Real experience

What I would check first

On a real P0618 fault, I would first check the battery history. If the battery has been flat, disconnected or jump-started, that can explain a memory fault, but I would still test whether the code returns after a proper reset and drive cycle.

Next, I would check permanent power at the alternative fuel control module. A KAM circuit needs live power even with the ignition off. If that feed disappears, the module may forget its stored values every time the car is parked.

If power, earths, fuses and wiring are all good, and the code keeps returning, then module memory, software or coding becomes more likely.

P0603 KAM Error P0607 Module Performance Diagnostic App
Common mistakes

Mistakes to avoid with P0618

P0618 can become expensive if power supply checks are skipped.

Replacing the module too quickly

A lost permanent live, weak battery or poor earth can make a good module look faulty.

Ignoring battery history

A flat battery, jump start or battery disconnection can trigger memory-related faults.

Only checking ignition live

KAM needs permanent power, not just power when the ignition is switched on.

Ignoring earth voltage drop

A ground may look connected but still have enough resistance to upset module memory.

Clearing the code without retesting

A real memory fault may only return after a key cycle, overnight park or battery voltage drop.

Ignoring water ingress

Moisture in connectors or fuseboxes can cause intermittent module memory faults.

MOT impact

Will P0618 fail an MOT?

P0618 itself is not usually the direct MOT failure item. The MOT concern is what the fault causes. If it causes an engine warning light, emissions problem, poor running, fuel system warning, limp mode or unsafe behaviour, it can become an MOT issue.

If the alternative fuel system is not working correctly, the vehicle may run poorly or produce emissions problems. It is better to diagnose repeated memory faults before the MOT, especially if warning lights or drivability symptoms are present.

⚠️ Higher risk: engine light, poor running, fuel smell, emissions issue, limp mode or repeated memory loss.

⚠️ Medium risk: stored KAM code, recent flat battery, intermittent alternative fuel warning.

✅ Lower risk: fault repaired, no warning lights, smooth running and normal fuel system behaviour.

Engine Light MOT Guide Common MOT Failures
Emissions and memory faults

Why KAM faults can affect emissions

If a control module loses learned fuel data, the engine may need to relearn fuel behaviour. During that time, idle quality, fuel economy and emissions can be affected.

A single memory fault after a flat battery may be less serious. A repeated P0618 after every key cycle is more concerning and should be diagnosed properly.

Engine Management Light Guide Fault Codes Hub
Used car buying advice

P0618 on a car you want to buy

If a used car has P0618 stored, ask more questions before buying. It may be a historic low-voltage code from a flat battery, but it could also mean the alternative fuel module is losing memory repeatedly.

Before buying, check whether the car starts cleanly, runs smoothly, switches fuel modes correctly and has any warning lights. Ask whether the battery has recently been replaced, whether the car has been standing, and whether the alternative fuel system has been repaired or modified.

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

✅ Check whether P0618 returns after clearing and restarting.

✅ Ask if the battery has been flat, replaced or disconnected.

✅ Check for P0562, P0603, P0607 or other module memory codes.

✅ Check alternative fuel operation during a proper road test.

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

Used Car Buying Guides Inspection Checklist
Negotiation warning

Do not ignore repeated KAM errors

A one-off memory fault after a flat battery may be understandable. A repeated P0618 that returns after every key cycle suggests a power feed, earth, wiring, software or module memory problem.

If the alternative fuel system has been modified, poorly installed or recently repaired, inspect it carefully. Poor wiring and bad power feeds are common causes of module memory problems.

Buying With Advisories Check MOT History
Frequently asked questions

FAQs about P0618

Common questions about P0618 alternative fuel control module KAM error, safe driving, repair costs, voltage faults and MOT impact.

What does code P0618 mean?

P0618 means the alternative fuel control module has detected a Keep Alive Memory error.

Is P0618 serious?

It can be serious if it causes poor running, limp mode, alternative fuel system faults or repeated memory loss.

Can I drive with P0618?

Short driving may be possible if the vehicle runs normally, but avoid driving if it runs badly, stalls, smells of fuel or enters limp mode.

Does P0618 mean the module is faulty?

Not always. Power supply, permanent live, earths, battery voltage, fuses, wiring and connectors should be checked first.

Can a weak battery cause P0618?

Yes. A weak or flat battery can trigger Keep Alive Memory faults in control modules.

Can a blown fuse cause P0618?

Yes. If the fuse supplies the module’s permanent memory feed, a blown fuse or poor fuse contact can cause P0618.

Will P0618 fail an MOT?

P0618 can affect an MOT if it causes warning lights, emissions problems, rough running, limp mode or fuel system faults.

Should I replace the module first?

No. Check battery voltage, permanent power feed, ignition feed, earths, fuses, wiring and software before replacing the module.

Can P0618 be cleared?

It may clear temporarily, but if the module keeps losing memory, the code will return.

How much does P0618 cost to fix in the UK?

Diagnosis may cost around £60–£150. Battery, fuse or wiring repairs may be cheaper, while module replacement and coding 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 P0618 guide is designed to help you understand alternative fuel control module Keep Alive Memory 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. P0618 can involve battery voltage, permanent power feed, ignition feed, fuses, relays, earth straps, wiring faults, connector corrosion, water ingress, software, coding and internal module memory. Proper testing is better than guessing.

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