P0603🔧 Engine computer (PCM) memory and power supplyStop and fix promptly

P0603: Internal Control Module Keep Alive Memory (KAM) Error (Meaning, Causes, Fixes)

Reviewed 2026-10-22 · Based on 2 cited source(s)

What P0603 means

OBD-Codes.com explains that the keep alive memory (KAM) is the part of the powertrain control module's (PCM) memory that stores learned values, such as fuel trims and shift adaptations, that change with driving and sensor inputs. It is kept alive by a constant battery feed, the keep alive power (KAPWR) circuit. Disconnecting the battery erases it and the PCM falls back on its built-in base settings until it relearns, which is not the same as limp mode. P0603 sets when the PCM detects an error in this memory. OBD-Codes.com calls it a generic code that applies to all 1996 and newer vehicles, though repair steps vary by model. The sources describe it differently: RepairPal's short explanation says P0603 sets when the PCM loses communication with one or more control modules, while OBD-Codes.com ties it to the PCM's own keep alive memory and its power supply. Related internal module codes are P0601 (memory checksum), P0602 (programming error), P0604 (RAM error) and P0605 (ROM error).

Severity: can I keep driving?

Stop and fix promptly

Get it checked soon. RepairPal rates P0603 Urgent, meaning immediate action is needed. OBD-Codes.com says the check engine light may be the only sign, but lists engine stalling and no-start conditions as possible symptoms. If the engine stalls or won't idle, don't rely on the vehicle, since stalling in traffic is a real safety risk.

Common symptoms

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

  1. Corroded battery terminals or loose battery connections (OBD-Codes.com)
  2. An open wire or poor routing in the keep alive power (KAPWR) circuit to the PCM (OBD-Codes.com)
  3. A charging system fault, such as alternator interference (OBD-Codes.com)
  4. An ignition system fault leaking high voltage into nearby wiring, such as cracked plug wires or coils (OBD-Codes.com)
  5. A damaged PCM, including water intrusion or an internal fault (OBD-Codes.com)
  6. An internal PCM software fault, or an aftermarket chip or tuner (OBD-Codes.com)
  7. Lost communication between the PCM and other control modules (RepairPal)
  8. The sources differ: RepairPal gives only module communication loss as the trigger, while OBD-Codes.com lists power, ground, interference and PCM causes and says it can be hard to isolate

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

  1. Clean and tighten the battery terminals and cables, and check the main grounds, fuse box and PCM connectors (OBD-Codes.com).
  2. Test the battery and charging system. A weak battery or bad alternator output can upset the PCM's power supply.
  3. Inspect wiring that runs near ignition parts, and check spark plug wires and coils for cracks where voltage could leak (OBD-Codes.com).
  4. If you have a multimeter, check the PCM power supply circuits while gently wiggling the harness around the engine and fuse boxes to find an intermittent drop (OBD-Codes.com).
  5. Look for signs of water getting into the PCM or its connectors (OBD-Codes.com).
  6. If an aftermarket tuner or chip is installed, return the PCM to stock programming and see if the code comes back (OBD-Codes.com).
  7. Check for technical service bulletins (TSBs) and PCM software updates for your vehicle (OBD-Codes.com).

Typical fixes

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

  • The engine stalls or won't start
  • Power and ground checks pass and the code returns, which can point to the PCM
  • The PCM needs a software reflash or replacement and programming, which needs dealer-level tools
  • Several module communication codes are stored at once

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Is P0603 serious?

It can be. RepairPal rates it Urgent, and OBD-Codes.com lists stalling and no-start as possible symptoms. Some cars run normally with it, but have it diagnosed soon.

Can a dead or disconnected battery cause P0603?

It can be related. OBD-Codes.com says disconnecting the battery erases the keep alive memory, and it lists corroded or loose battery connections as a cause. Check the battery and its cables before suspecting the computer.

Do I need a new PCM for P0603?

Not necessarily. OBD-Codes.com says it has been caused by both wiring and PCM faults, and some cases are fixed with a software reflash. Check power, grounds and wiring first.

How much does it cost to fix P0603?

Neither source gives a repair cost. It can range from cleaning a battery terminal to a reflash or PCM replacement, so get a diagnosis or a written estimate first.

Sources

  1. OBD-Codes.com: P0603 Internal Control Module Keep Alive Memory (KAM) Error
  2. RepairPal: P0603 Internal Control Module Keep Alive Memory (KAM) Error (rated Urgent)

Last reviewed 2026-10-22. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.