P0603low severityGenerally driveableP0603 Code: Internal Control Module Keep Alive Memory (KAM) Error
Written in plain English and reviewed by the eli5cars editorial team · Last reviewed June 2026
What it means in plain English
Your engine computer (PCM/ECM) constantly learns and saves adjustment values while you drive — things like fuel trims, idle settings, and transmission shift adaptations — in a special memory area called Keep Alive Memory (KAM) that stays powered even with the engine off, as long as the battery is connected. P0603 means the PCM detected that this saved data was lost, corrupted, or couldn't be read correctly. This is most often triggered by something interrupting power to the PCM — a dead or disconnected battery, a loose terminal, or a voltage dropout — rather than an actual defect in the computer itself.
Most likely causes — ranked
#1 Recent battery disconnection, a dead battery, or a battery that was fully drained
most likelyFix: If the battery was recently disconnected for a repair, went completely dead, or was replaced, the PCM's Keep Alive Memory loses its saved adaptive values, which can trigger this code the next time it's checked. Charge or replace the battery as needed, clear the code, and drive the vehicle through several normal start-stop cycles — this lets the PCM relearn its idle and fuel trim values, and the code typically won't return.
#2 Loose, corroded, or damaged battery terminal/cable connections
likelyFix: Even a battery in good health can cause KAM errors if its connection to the vehicle's electrical system is unreliable. Inspect both battery terminals and cables for corrosion, looseness, or damage. Clean corroded terminals with a wire brush and baking-soda solution, and make sure the cable clamps are tight.
#3 Voltage spikes or an unstable charging system from a failing alternator
likelyFix: An alternator producing excessive electrical noise or voltage outside the normal range can intermittently disrupt the PCM enough to corrupt KAM data. Have the charging system tested — most parts stores do this for free. Replace the alternator if its output is out of spec.
#4 Internal PCM/ECM fault preventing KAM from storing or retaining data correctly (rare)
possibleFix: If the battery, cables, and charging system all check out and the code keeps returning after being cleared and relearned, the PCM itself may have an internal memory fault. This is uncommon and should only be considered after eliminating the power-supply causes above — a shop with factory diagnostic tools can confirm before recommending PCM replacement.
Check engine light on? Get a free code scan
If your check engine light is on, most auto-parts stores (AutoZone, O'Reilly, Advance) will read the code for FREE — no purchase required, just walk in. Bring the code back here and look it up at eli5cars.com/obd2 for the plain-English explanation.
Note: a scan only helps when there's an active fault code. For purely mechanical symptoms (noises, vibrations, leaks), a scan may show nothing — the suspects listed above are your starting point.
Want to read the codes yourself?
First, the free option: AutoZone, O’Reilly, and Advance Auto Parts read your codes for free — no purchase needed. That’s the cheapest way to get the code to look up here. If you’d rather have your own so you can check anytime (and clear a code after a fix), the Veepeak OBDCheck BLE is an inexpensive, reliable plug-in reader that pairs with a free phone app and works on any car sold since 1996.
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Frequently asked questions
Can I drive with P0603?
Yes. This code by itself doesn't affect drivability — the PCM simply needs to relearn its adaptive values. You may notice slightly rougher idle or shifting for a short period until it relearns.
Will this code clear itself?
Often yes — once the PCM has relearned its idle, fuel trim, and (on automatics) transmission adaptive values over a normal drive cycle, the code typically doesn't return on its own. If it keeps coming back, that points to an ongoing power supply issue rather than a one-time event.
I just replaced my battery and got this code — is that normal?
Yes, this is one of the most common triggers for P0603. Disconnecting the battery wipes the PCM's Keep Alive Memory. Clear the code and drive normally for a while; it should not return unless there's an underlying electrical issue.
Does P0603 mean my PCM is failing?
Not usually. The far more common cause is something interrupting power to the PCM — a battery, cable, or charging system issue — rather than the computer's internal memory hardware actually being defective. Rule out the electrical basics before assuming the worst.