What Does P0603 Mean?
P0603 indicates that the ECM/PCM has detected an error in its Keep Alive Memory (KAM). KAM stores learned values such as fuel trim adjustments, idle speed corrections, and adaptive transmission shift data that the ECM retains when the vehicle is turned off. When KAM is lost or corrupted, the engine may run poorly until it relearns these values. The driver may notice rough idle, hesitation, and the check engine light.
Common Causes
35%
Battery disconnected or dead, causing KAM data loss
25%
ECM/PCM constant power circuit interrupted (blown fuse, corroded connector, wiring fault)
20%
Internal ECM/PCM EEPROM or KAM circuit failure
12%
Parasitic drain causing battery voltage to drop below KAM retention threshold
8%
Corroded or loose battery cable connections causing intermittent power loss
Diagnostic Steps
1
Check the ECM keep-alive power fuse — it should have battery voltage (12V+) on both sides with the key off. If blown, replace and check for shorts in the circuit.
2
Measure battery voltage: should be 12.4-12.8V with engine off. If below 12V, load test the battery. Check alternator output at 13.5-14.7V at idle.
3
Inspect battery terminals and cable ends for corrosion — clean with a wire brush and apply dielectric grease. Verify cable tightness; they should not rotate by hand.
4
Measure the voltage at the ECM constant power pin with key off — it should show battery voltage. If not, trace the circuit from the fuse box to the ECM for opens or high resistance (voltage drop should be under 0.1V).
5
If power supply is confirmed good and the code persists after clearing, the ECM has an internal KAM failure and requires replacement.
Estimated Repair Cost
$50 - $1,200
Parts + labor, varies by vehicle and location
P0603 indicates that the ECM/PCM has detected an error in its Keep Alive Memory (KAM). KAM stores learned values such as fuel trim adjustments, idle speed corrections, and adaptive transmission shift data that the ECM retains when the vehicle is turned off. When KAM is lost or corrupted, the engine ...
The most common cause of P0603 (Internal Control Module Keep Alive Memory (KAM) Error) is: Battery disconnected or dead, causing KAM data loss
Typical repair costs for P0603 range from $50 to $1,200, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Generally safe to drive short distances, though the vehicle may idle roughly or hesitate until the ECM relearns its adaptive values (typically 50-100 miles of mixed driving). If the code keeps returning, it could indicate an ECM failure that may worsen. Avoid long trips until resolved.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0603 to identify the root cause.
OBDHut Mobile App
Scan codes directly from your car with the OBDHut app.
Coming Soon
Quick Info
Category
Powertrain
System
Engine Control Module
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
