OBD-II Diagnostic Trouble Code
P0603 — Internal Control Module Keep Alive Memory (KAM) Error
P0603 means the control module detected a fault in its keep-alive memory, the memory that holds learned values (fuel trims, idle and transmission adaptives) while the key is off. The module saw the stored data was lost or invalid, usually because its constant battery power was interrupted.
Severity 3/5
Truck-relevant
Service this week
Severity
Service this week
Internal Control Module Keep Alive Memory (KAM) Error
Code
P0603
Category
Powertrain
Subsystem
Network
Truck-relevant
Yes
What this means for truckers
P0603 (Internal ECM KAM Error) — Keep-Alive Memory error. Battery may have been disconnected, or KAM circuit has a fault.
Before you replace parts — try this first
P0603 on the Network system is most often batteries disconnected, discharged or replaced, wiping the memory — not a dead part. On commercial diesels especially, work these in order before spending money on parts:
- Confirm the symptoms. Match what your truck is doing to the Symptoms section below. If the code is set but the symptoms are not there, clear the code and re-test after a drive cycle — it may not return.
- Clean and dry the sensor connector. Water, road salt, or oil seeping into a connector is the #1 fake sensor failure. Disconnect, look for green corrosion or moisture, spray with electrical contact cleaner, dry, reseat. Many faults clear here for $0.
- Inspect the wiring harness. Trace the wire from the sensor toward the ECM — look for chafing against the engine block, melted insulation near the turbo or exhaust, or pinch points where a clamp has rubbed through.
- Test the sensor before swapping it. Most Common Causes (below) list the expected voltage or resistance range — a $20 multimeter saves a $300 sensor swap that does not fix the problem.
- Only then, replace the part. Use the OEM or a tier-1 aftermarket. Cheap sensors throw the same code in two weeks.
Symptoms
Often there's no driveability symptom beyond the check-engine light. Idle quality, shift feel or fuel economy may be off for a while as learned values relearn. If it keeps coming back, suspect a constant-power problem that also causes a no-start or a dead battery.
Common causes
- CommonBatteries disconnected, discharged or replaced, wiping the memory ($0–$150)
- CommonBlown fuse or poor connection in the ECM's constant battery feed ($50–$300)
- OccasionalCorroded battery cables or a poor ECM ground ($100–$400)
- RareInternal ECM memory fault ($1200–$3500)
How to fix
Clear the code and see whether it comes back after several key cycles
When to use: When the batteries were recently disconnected or replaced
Check the ECM's constant battery feed fuse and circuit, and test voltage at the ECM connector with the key off
When to use: When the code keeps coming back
Clean and tighten the battery terminals, the main grounds and the ECM ground
When to use: When there's voltage drop or corrosion
Reflash or replace the ECM
When to use: Only when power and grounds test good and the code comes back right away
Affects most
No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.
Related
- → Browse all DTC trouble codes
- → Decode a VIN to check codes for your truck
- → Owner-operator maintenance guides
- → P0670 — Glow Plug Control Module Circuit
- → P0671 — Cylinder 1 Glow Plug Circuit
- → P0672 — Cylinder 2 Glow Plug Circuit
- → P0673 — Cylinder 3 Glow Plug Circuit
- → P0674 — Cylinder 4 Glow Plug Circuit
Frequently Asked Questions
Can I drive with code P0603?
P0603 is severity 3 — plan service within a few days. Performance is likely degraded already (you may feel reduced power, harsher shifts, or slightly worse fuel economy). Continuing to drive risks additional damage to adjacent components.
How much does it cost to fix P0603 on a commercial truck?
Total repair cost ranges varies depending on the root cause. The cheapest fix is usually the first one listed below — Batteries disconnected, discharged or replaced, wiping the memory — which is also the most common. On commercial trucks the cost is usually higher than passenger vehicles due to part availability and shop labor rates ($120–185/hour at most truck shops, vs $90–130 at general auto shops). DIY-capable fixes (sensors, hoses, filters) are at the low end; major component replacements (turbo actuator, high-pressure fuel pump, transmission solenoid pack) are at the high end. Always diagnose with a scan tool BEFORE replacing parts — guessing wrong on a $1,500 turbo actuator when the actual issue was a $30 boost hose is a common expensive mistake.
Will P0603 fail a DOT inspection?
P0603 is generally not a direct DOT inspection fail item by itself. Inspectors focus on safety-critical systems (brakes, steering, tires, lights, hours-of-service). However, the check engine light alone can trigger additional inspection scrutiny. Best practice: fix the code and clear it before a planned inspection.
What's the difference between P0603 and related codes?
P0603 is closely related to: P0670 (Glow Plug Control Module Circuit), P0671 (Cylinder 1 Glow Plug Circuit), P0672 (Cylinder 2 Glow Plug Circuit), P0673 (Cylinder 3 Glow Plug Circuit). These codes share the same subsystem (network) and often appear together. If you see this code, scan for the full code list — fixing the root cause usually clears multiple companion codes at once. If only P0603 is set without the companions, the issue is more isolated.
How do I prevent P0603 from coming back after a repair?
For P0603 (Internal Control Module Keep Alive Memory (KAM) Error), prevention centers on the network system. Pay attention to ground connections at every PM — bad grounds are 70% of communication codes. Inspect harness routing for chafe points. Don't disconnect modules with the key on.