P0603
Internal Control Module Keep Alive Memory (KAM) ErrorP0603 is a generic OBD-II powertrain diagnostic trouble code: Internal Control Module Keep Alive Memory (KAM) Error. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0603 means
P0603 indicates that the powertrain control module (PCM) has failed its internal self-test of the Keep Alive Memory (KAM). KAM is a small section of non-volatile RAM inside the PCM that retains adaptive fuel trim values, idle relearn data, transmission shift adaptations, and other learned calibration parameters even when the ignition is switched off. It is kept powered by a constant 12 V feed directly from the battery (not switched through the ignition). If that feed drops or the memory fails its integrity check, P0603 is set.
The most frequent cause is loss of the always-on battery voltage to the PCM — a blown memory-keep fuse, a corroded fuse holder, or a momentary disconnection during battery service. Unlike P0602, the module's main program is intact; only the learned adaptive data is lost or unreadable. The PCM then reverts to base calibration tables, which can result in noticeably different drivability until the module relearns its adaptations over several drive cycles.
Less commonly, the KAM memory cell itself degrades on older modules, particularly on high-mileage vehicles that have experienced repeated deep-discharge events. In these cases the fault returns shortly after clearing, even with a healthy fuse circuit, and module replacement becomes necessary. A weak or failing battery that hovers near its minimum keep-alive voltage threshold overnight can also cause intermittent P0603 without a blown fuse.
On vehicles equipped with a TCU (transmission control unit) with its own KAM circuit, a related code may appear alongside P0603. The repair is typically straightforward — restore the constant voltage feed, correct any ground faults, and allow the PCM to complete its relearn cycle. Only replace the module after confirming the power supply and grounds are solid.
Common causes
Most-frequently reported root causes when P0603 is logged.
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1
Blown or corroded memory-keep fuse supplying constant 12 V to PCM
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2
Battery disconnection or deep discharge wiping KAM contents
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3
Corroded or loose PCM ground connection
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4
Weak or failing vehicle battery unable to maintain keep-alive voltage
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5
Faulty wiring in the constant-power feed circuit to the PCM
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6
Degraded internal KAM memory cell in an aged or high-mileage module
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7
Short circuit on an accessory (e.g., cigarette-lighter adapter) blowing the keep-alive fuse
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8
Recent battery replacement without PCM relearn procedure
Symptoms drivers notice
How to diagnose P0603
A typical diagnostic flow when this code is present.
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1
Scan all modules for DTCs and note any battery or communication codes stored alongside P0603
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2
Measure battery voltage at rest (should be ≥12.4 V) and check for a failing battery under load
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3
Locate and inspect the PCM keep-alive memory fuse (refer to the vehicle's fuse chart for the constant-power fuse); replace if blown
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4
Check for voltage at the PCM keep-alive feed pin with the ignition off; should read battery voltage
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5
Inspect PCM ground straps for corrosion and verify resistance to chassis ground is less than 0.1 Ω
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6
Clear the code and monitor whether it returns with the ignition off overnight — a return indicates insufficient keep-alive voltage
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7
If the fault persists after confirming a solid power/ground supply, replace and reprogram the PCM as the internal KAM cell is likely degraded
Related powertrain codes
Frequently asked questions
Does P0603 mean I need a new PCM?
Not usually. The most common fix is restoring the constant 12 V feed — replacing a blown fuse or repairing corroded wiring. Module replacement is only needed when the KAM cell itself has physically failed, which is confirmed by the fault returning after the power circuit is verified healthy.
Will the car drive normally after clearing P0603?
Initial drivability may be slightly off because adaptive fuel trim and transmission shift data are reset. The PCM will relearn these values over several complete drive cycles, after which performance should return to normal.
Can disconnecting the battery cause P0603?
Yes. Disconnecting the battery wipes KAM contents. On vehicles with strict memory self-tests, the PCM can flag P0603 on the next startup. The code usually clears itself after a drive cycle once the module confirms its memory is functional.
Is P0603 related to P0600 or P0602?
They are related but distinct. P0600 covers general serial communication faults, P0602 indicates a programming/checksum error in the module's firmware, and P0603 specifically targets the keep-alive RAM section. Each has a different diagnosis path.
Disabling P0603 in software
RaceTune can permanently disable P0603 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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