P0603
Internal Control Module Keep Alive Memory (KAM) Error
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The P0603 code means the Powertrain Control Module (PCM) has lost its Keep Alive Memory (KAM). KAM is a special section of the PCM's memory that stores learned values and adaptive data even when the vehicle is turned off. This includes fuel trim adjustments, idle speed corrections, and transmission shift adaptations that the PCM has learned over time to optimize your vehicle's performance.
When KAM is lost, the PCM essentially forgets everything it has learned about how your specific engine runs best. You may notice rough idle, hesitation, harsh transmission shifts, and poor fuel economy for a period after the code sets. The vehicle will eventually relearn these values through normal driving, but the underlying cause of the memory loss needs to be addressed to prevent it from happening again.
The good news is that the most common cause is simply a weak battery or poor battery connections — making this one of the more DIY-friendly ECM codes. Start by testing your battery and cleaning the terminals. Check the fuses related to the PCM's constant power supply. If the battery and connections are in good shape and the code keeps returning, the issue may be in the wiring to the PCM or potentially an internal PCM failure, which would require professional diagnosis and possible module replacement.
Severity
Symptoms
- •Check engine light illuminated
- •Engine idles roughly or stalls after being restarted
- •Poor fuel economy or sluggish performance until the car relearns driving patterns
- •Transmission may shift harshly or at incorrect points
- •Climate control, radio presets, or other comfort settings may reset
Likely Causes
Keep Alive Memory is powered by the battery even when the vehicle is off. A weak, dying, or disconnected battery causes KAM data to be lost, triggering this code. This is especially common after battery replacement or a dead battery event.
Poor connections at the battery terminals can cause intermittent voltage drops that wipe the KAM. Even a brief loss of power can erase the PCM's learned data.
A blown fuse in the constant battery power feed to the PCM, or a wiring fault in the always-on power circuit, prevents KAM from being maintained when the vehicle is off.
In some cases, the KAM circuit within the PCM itself has failed, meaning it cannot retain learned values regardless of external power supply conditions.
Estimated Cost
Professional Repair
Includes parts + labor
Common Fixes
- Test and replace a weak or failing battery
- Clean and tighten battery cable connections and terminals
- Check and replace any blown fuses in the PCM constant power circuit
- Inspect the PCM wiring harness for damage to the always-on power feed
- Replace the PCM if internal KAM circuit failure is confirmed