OBD-II trouble code
P0603: Internal Control Module Keep Alive Memory (KAM) Error
The PCM's Keep Alive Memory — the data it retains between key cycles, like learned fuel trims and idle settings — failed its self-check. Very often caused by a weak battery, a bad ground, or a recently disconnected battery, and frequently fixed with a simple power-side repair.
Quick facts
- System
- Powertrain
- Category
- PCM / Electronics
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $50 – $1,400
- DIY difficulty
- Intermediate DIY
What does P0603 mean?
Keep Alive Memory (KAM) is the part of the PCM's memory that holds learned, adaptive data when the engine is off — things like long-term fuel trims, idle adaptations, transmission shift adapts, and other values the computer fine-tunes over time. Unlike the main program, KAM relies on a continuous low-current power feed (a 'keep alive' or memory circuit) so the data survives between drives. P0603 sets when the PCM checks this memory and finds it didn't retain its data correctly or the keep-alive circuit isn't behaving as expected.
What makes P0603 different from the other PCM-internal codes is how often it traces to something simple on the power side. A weak or dying battery, a corroded battery terminal, a bad ground, or a blown memory-circuit fuse can all interrupt the keep-alive feed and wipe or corrupt KAM. The code very commonly appears right after a battery has been disconnected, replaced, or run completely flat. In those cases the fix is on the power side, not the computer — and the PCM simply needs to relearn its adaptive values as you drive.
Because KAM holds adaptive rather than critical run data, P0603 is usually less severe than codes like P0601 or P0602. The engine typically still runs, though you may notice a rough or hunting idle, slightly off shifting, or reduced fuel economy until the PCM relearns its trims. Persistent P0603 that returns after the battery and grounds are confirmed good points toward an internal memory or keep-alive circuit fault in the PCM itself.
Common causes
- Weak, dying, or recently dead battery interrupting the keep-alive feed
- Corroded or loose battery terminals
- Poor or corroded PCM ground connection
- Battery recently disconnected or replaced (KAM lost)
- Blown memory-circuit (keep-alive) fuse
- Damaged or corroded wiring on the keep-alive power circuit
- Internal PCM memory or keep-alive circuit failure (after power side is ruled out)
Symptoms
- Check engine light on with P0603 stored
- Rough or hunting idle, especially right after the code sets
- Slightly harsh or delayed transmission shifts until relearned
- Temporary reduction in fuel economy
- Code often appears after a battery disconnect, replacement, or dead battery
- Generally normal driveability otherwise
Diagnostic steps
- 1.Test the battery and charging system. A weak battery or low charging voltage is the single most common cause of P0603.
- 2.Inspect and clean the battery terminals and check every major engine and chassis ground for corrosion or looseness.
- 3.Check the keep-alive / memory-circuit fuse and its associated wiring for an open or blown fuse.
- 4.Note whether the battery was recently disconnected, replaced, or run flat — that history usually explains the code.
- 5.Clear the code, then drive the vehicle through a relearn cycle and see whether it returns.
- 6.Scan for related PCM-internal codes (P0601, P0604, P0605) that might indicate a broader memory problem.
- 7.If P0603 returns with a known-good battery, clean grounds, and an intact keep-alive circuit, the PCM has an internal fault and needs replacement and programming.
Repair cost
$50 – $1,400
Most P0603 cases are inexpensive: a battery replacement is $120-$300, and terminal or ground cleaning/repair is $50-$200 — these resolve the majority of cases. A blown memory-circuit fuse or wiring repair is $50-$250. Only if the memory hardware has genuinely failed does PCM replacement plus programming apply, at roughly $800-$1,400. Start with the battery and grounds; replacing the PCM for P0603 without checking the power side first is a common and avoidable mistake.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with battery replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.