What is Keep Alive Memory and why does losing it matter?

It is the part of the controller's memory that stays powered when the ignition is off, held up by a small permanent feed from the battery, and it stores what the controller has learned about your specific vehicle rather than what it was programmed with at the factory — fuel trims, learned actuator positions, idle adaptations. Losing it does not break the controller. It makes it forget, so it reverts to base calibration and the vehicle runs the way it did before any adaptation had happened. On a factory bi-fuel car that is a few rough days. On an aftermarket conversion, where those adaptations were doing real work, the difference can be much more noticeable.

Does this mean I need a new alternative fuel control module?

Usually not, and it is worth resisting that conclusion for a while. Because this memory is kept alive by battery power with the key off, the most common causes sit in the power path rather than in the module: a tired battery, a corroded terminal, a missing or blown fuse on the permanent feed, or a high-resistance ground. Any of those can wipe learned memory while the vehicle still starts and drives normally, so nobody suspects a supply problem. Check those first — they are cheap, quick, and account for a large share of this code.

Can this be caused by simply disconnecting the battery?

Yes, and it is one of the most frequent triggers. Disconnecting the battery, replacing it, jump-starting the vehicle or letting it go flat while parked all interrupt the standby supply that holds this memory. On a controller whose retention is already marginal, that is enough to set the code. If the fault appeared right after battery work, clear it, drive the vehicle normally for several days, and see whether it returns — a one-off that never comes back is consistent with a simple power interruption rather than a fault.

My alternative fuel system was fitted after the car was built. Does that change anything?

It changes quite a lot. A converted vehicle's controller usually takes its permanent power from a splice into an existing circuit rather than from a dedicated factory-fused supply, and its ground is often taken to a convenient body point. Those joints are the standard weak spot, and they will not appear on the vehicle manufacturer's wiring diagram, so finding the installation wiring is part of the job. It also affects who can help: alternative fuel controllers are frequently outside generic scan tool coverage and are supported by the conversion system's manufacturer rather than by the car's dealer network, so it is worth establishing who holds the software before booking the car in anywhere.

OBD-II trouble code

P0618: Alternative Fuel Control Module KAM Error

Keep Alive Memory is everything the controller learned about your specific vehicle, and it is held there by battery power with the key off. That is why the leading cause of this code is not the module — it is the power path that keeps the module's memory alive overnight.

Medium severityPowertrainPCM / ElectronicsDrivable short-term

Quick facts

System: Powertrain
Category: PCM / Electronics
Severity: Medium severity
Drivable: Usually safe to drive short-term
Repair cost range: $80 – $1,600
DIY difficulty: Shop recommended

What does P0618 mean?

P0618 is set when the alternative fuel control module reports a fault with its Keep Alive Memory. It applies to vehicles that run on something other than conventional petrol or diesel — compressed natural gas, liquefied petroleum gas, and various bi-fuel arrangements — and it concerns a specific kind of memory inside that controller rather than the fuel system itself.

Keep Alive Memory is worth understanding properly, because the name gets used loosely and the distinction is what makes this code make sense. It is the area of memory that stays powered when the ignition is switched off, held alive by a small permanent feed from the battery. Its job is to store what the controller has learned about this particular vehicle rather than what it was programmed with at the factory: fuel trim corrections, learned actuator positions, idle adaptations, the accumulated small adjustments that turn a generic calibration into one that suits this engine, this fuel supply and this installation.

That tells you what a KAM error actually costs you, and it is a more subtle answer than 'the module is broken'. The controller still works. Its program is intact and it can still run the engine. What it has lost is everything it learned, so it falls back on base calibration — and the vehicle runs the way it ran on the day the system was first commissioned, before any adaptation. On a factory bi-fuel car that is merely a bit rough for a few days. On an aftermarket conversion, where the base calibration was only ever a starting point that the adaptations were quietly correcting, it can be markedly worse: poor idle, hesitation, higher consumption and stalling on the alternative fuel.

The second and more useful consequence is where to look. Because this memory is kept alive by battery power with the key off, the most common cause is not a failed module at all — it is the power path. A battery that has been disconnected, replaced, jump-started or simply run down overnight interrupts the standby supply. So does a corroded battery terminal, a high-resistance ground, or a missing fuse on the permanent feed circuit. Every one of those wipes or corrupts learned memory while leaving the vehicle starting and driving well enough that nobody suspects an electrical supply problem. Checking the battery, its terminals, the constant-power fuse and the controller's ground is cheap, quick and resolves a large share of these codes.

The third fact worth stating plainly is about the population of vehicles that set this. Many of them were not built as alternative fuel vehicles — they were converted afterwards, often by a specialist installer, sometimes years ago and sometimes by somebody who is no longer trading. A converted vehicle's controller usually takes its permanent feed from a splice into an existing circuit rather than from a dedicated factory-fused supply, and that splice is the weak point. A crimp that was never soldered, insulation tape that has unwound behind a kick panel, a ground taken to a painted seat bolt: these are ordinary findings on converted vehicles and they produce exactly this fault. Finding the installation wiring is a real part of the job here, and it is not documented in the vehicle's factory wiring diagram.

One practical note on who can help. Alternative fuel controllers are frequently outside generic scan tool coverage and are often supported by the conversion specialist rather than by the vehicle manufacturer's dealer network. Establishing who holds the software and the wiring documentation for your particular installation is worth doing before booking the car in anywhere, because a main dealer may not be able to communicate with the module at all.

The vehicle remains driveable in most cases, and on a bi-fuel vehicle it can normally be run on petrol while the fault is investigated. It is not filed as trivial, though, because a controller running on base calibration is a controller not correcting for anything, and prolonged operation with badly wrong mixture on the alternative fuel is hard on catalytic converters and, on gas systems, on valve seats.

Common causes

Weak or failing battery unable to hold the standby supply overnight
Corroded or loose battery terminal interrupting keep-alive power
Missing or blown fuse on the alternative fuel controller's permanent feed
High-resistance ground for the alternative fuel controller
Poorly made splice in an aftermarket conversion's permanent power feed
Battery disconnected, replaced or jump-started, wiping learned memory
Vehicle left standing long enough for the battery to discharge below retention voltage
Water ingress into an aftermarket controller or its connector
Failed alternative fuel control module with a genuine internal memory fault
Aftermarket accessory wired into the same permanent feed and loading it down

Symptoms

Rough or unstable idle on the alternative fuel
Hesitation and poor acceleration that improves over several days of driving
Noticeably worse fuel consumption on the alternative fuel
Stalling shortly after switching from petrol to gas
Harsh or delayed shifting on some installations
Check engine light after the battery was disconnected or replaced
System refusing to switch to the alternative fuel until warmed up
Fault appearing after the vehicle has been standing unused for weeks

Diagnostic steps

1.Start at the battery, because Keep Alive Memory is battery-backed by definition and this code is frequently a power supply story rather than a module story. Load-test the battery, check its resting voltage after a night parked, and inspect both terminals for the soft green powder that forms under a clamp and is invisible until the clamp comes off. A battery that drops low overnight, or a terminal that has enough resistance to interrupt the small standby current, will wipe or corrupt learned memory without ever leaving you unable to start.
2.Confirm the constant power feed and the ground to the alternative fuel controller specifically, and confirm them with the key off. This is a different circuit from the module's switched supply. Find the fuse that provides the permanent feed, check it is present and correct — it is not unusual to find it missing entirely after a workshop pulled it to avoid a parasitic drain complaint — and verify voltage at the module connector with everything shut down.
3.Ask directly whether the battery has been disconnected, replaced, jump-started or run flat recently, and whether the vehicle sits for long periods. Every one of those interrupts the standby supply, and on a controller with marginal memory retention that is enough to set this code. It is also the most likely explanation for a code that appeared once, was cleared, and has not returned.
4.Establish whether the alternative fuel system is factory-fitted or an aftermarket conversion, because the answer changes where you look and who you call. A converted vehicle has a controller that somebody installed and wired, and its permanent feed is very often a splice into an existing circuit rather than a dedicated fused supply. Find that splice. Poorly crimped, taped and left behind a trim panel is the standard installation, and it is exactly the kind of joint that goes high-resistance after a few winters.
5.Check the ground for the controller with a voltage drop test under load rather than a continuity check. Aftermarket installations frequently ground to a convenient body panel or a seat bolt rather than to a proper chassis point, and paint, underseal and corrosion at that point produce a memory fault that comes and goes with the weather.
6.Read what the controller actually holds before you clear anything, if your tool can. The adaptive values in Keep Alive Memory are diagnostic information in themselves — fuel trims well away from centre, learned actuator positions at the end of their range, or values sitting at obvious defaults tell you either that the memory has just been wiped or that the system has been compensating hard for a separate, unaddressed fault.
7.Expect and explain a relearn period after any repair. Once the memory has been lost, the controller reverts to base calibration and has to rebuild its adaptations over a number of drive cycles. Imperfect running in the days after the fix is normal and is not a failed repair — but if the running has not settled after a week of mixed driving, look for the underlying fault the old adaptations were hiding.

Repair cost

$80 – $1,600

Diagnosis is $90 to $200, and can be higher if the alternative fuel controller is outside standard scan tool coverage and a specialist has to be involved. The cheap and common outcomes come first: a battery is $120 to $350 fitted, cleaning and re-terminating a corroded battery connection is $40 to $120, and a fuse or a repaired permanent-feed splice is $60 to $220. Repairing or re-making an aftermarket installation's power feed and ground properly runs $120 to $400 depending on how much trim has to come out to reach the wiring. Replacing an alternative fuel control module is $350 to $1,600 including configuration, and on a converted vehicle the part usually has to come from the conversion system's manufacturer rather than from the vehicle manufacturer. Note that after any repair the controller has to relearn its adaptations over several drive cycles, so imperfect running for a few days afterwards is expected.

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DIY vs shop

Leave this one to a qualified shop. It typically involves emissions-critical components, refrigerant handling, or other work that requires manufacturer-grade tooling, training, or certification. DIY attempts often produce a more expensive problem than the original code.