1. Home
  2. /
  3. Complete List of OBD2...
  4. /
  5. P0603 – What Does...

P0603 – What Does It Mean and How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.


DTC Code P0603: Internal Control Module Keep Alive Memory (KAM) Error


DTC Code P0603 is a generic trouble code that is applicable to all OBD-II equipped vehicles (vehicles from 1996 till date). This trouble code indicates that the Powertrain Control Module (PCM) has failed in the Keep Alive Memory (KAM) self-test. This OBD-II code is stored when the PCM is working on its default parameters, while it ought to work with the information stored from drive cycles. The drive cycle, which is also the Keep Alive Memory (KAM), is the memory stored in the PCM.

This memory is constantly changing depending on the two major inputs, which are the driving inputs and the sensor inputs. However, this memory is erased the moment the battery is disconnected, and when this memory is erased, the computer goes into “numb” mode. This is because the KAM uses the in-built parameters to run the engine.

Even though this code is applicable to all OBD-II equipped vehicles, there is slight variation in the definition, troubleshooting methods, and repairs from one vehicle model to another.


There are a number of malfunctions that could lead to the presence of this code in a vehicle. Nevertheless, these faults are usually associated with the battery connection, the connection of the KAM system, as well as the PCM. Here are some of the common causes of P0603 in a vehicle:

  • The battery terminal is corroded
  • The connections of the battery terminal are loose
  • Low battery charge
  • Faulty or defective charging system
  • Open wire in the Keep Alive Power (KAPWR) circuit
  • Routing of the KAPWR circuit wire
  • Defective ignition system which results in the secondary ignition voltage inference
  • Internal fault with the Powertrain Control Module (PCM) program
  • PCM power supply circuit is either open or shorted


As in the case of other OBD-II codes, the first symptom of DTC P0603 is the illumination of the Check Engine Light (CEL). However, the symptoms can go beyond the mere illumination of the malfunction light. 

The symptoms of this code may vary from just the illumination of the CEL to difficulty in starting, amongst others. When no other fault is detected in the vehicle, it means the code is stored and the fault occurs intermittently. Here are the common symptoms you are most likely to encounter in a vehicle with P0603:

  • Illumination of the Check Engine Light (CEL)
  • Illumination of other warning lights
  • Misfires
  • Stalling of the engine
  • Difficulty in engine startup
  • Erratic or harsh shifting in transmission
  • Rough running
  • Rough idle


Diagnosing this OBD-II code, as stated earlier, varies depending on the make or model of your vehicle. However, there are diagnostic processes that are the same for all vehicles regardless of the make or model. 

The fault responsible for the presence of P0603 may vary from as simple as loose connections or corrosion on the terminal to a more severe problem as a faulty PCM. Therefore the diagnostic processes require expert attention in order to detect the exact cause of this problem. Nevertheless, here are some common diagnoses that can be conducted on your vehicle if you detect the presence of this error code:

  • Start the diagnosis by charging the battery
  • Then proceed to inspect the battery cables for loose connections and fix any connection issues detected
  • Also, check all ground connections as well as the fuse box and the PCM connections
  • Next, inspect the charging system for any irregularities
  • Having done that, run the car, first with the alternator connected, this may cause interference coming from the alternator
  • Then, run the car again with the alternator disconnected and see if the code returns
  • Should the code return, continue the diagnosis by inspecting the wiring harness across the vehicle’s ignition system
  • Also, inspect the spark plug wires and coil, looking out specifically for cracks. Equally, inspect other places where ignition voltage can leak
  • With the aid of a voltmeter, locate the power supply circuits that run towards the PCM
  • Once located, wiggle, bend or shake the harness all around the engine and fuse boxes while monitoring the voltages during the process 
  • Another important diagnostic process is the thorough inspection of the PCM itself. The PCM is usually isolated in a separate compartment in some vehicles, this may allow water to easily gain entrance into the PCM and cause a malfunction. Or, may result in vibrator transfer
  • If after the inspection, you discover that none of this has happened, then there is a high chance that the PCM itself is faulty. You should repair or replace it in this case
  • As a final tip, in vehicles that use an aftermarket chip or program, this may be the source of the problem. Meanwhile, there is usually a periodic software update by the manufacturers, you can look up any available update.

Also Read: Can A Bad Alternator Cause Engine To Shake

Common mistakes

While this trouble code may not be severe in some vehicles, there is a need to tread carefully, especially while conducting the diagnosis. A common diagnostic mistake that occurs in the process is the failure to check idle voltage and ground connections. Also, ensure that you charge the battery before you begin the diagnostic process.

How Serious is P0603?

With a careful analysis of the causes and the diagnosis of this code, you will observe that the presence of DTC code P0603 can be directly linked to a faulty PCM. This implies that the presence of this code could equally result in other more severe codes. This is because the powertrain control module is directly linked with the OBD-II system.

More so, the PCM controls a vast array of essential systems of a car, including the ignition, engine timing, fuel/air mixture, transmission, among others. Thus, it is safe to say that a defective PCM is tantamount to a vehicle’s breakdown. As a result, you need to diagnose the car as soon as you detect the presence of this trouble code.

What repairs can fix the code?

repair manualsrepair manuals

Having successfully diagnosed your vehicle with this code, here are some repairs that can be carried out to ensure the code is successfully cleared:

  • Consider replacing your battery and the alternator
  • Repair or replace defective or spoilt connectors, components, and wirings, and ensure a secured connection of the components
  • Repair or replace all defective components in individual control modules
  • Consider replacing defective PCM or battery grounds

Related codes

There are some other codes that are related to this trouble code, these codes include other OBD-II codes that also deal with the malfunction of the internal control module, they include:


Although the approaches to this code in different vehicle make or model differs, the tips given in this article are a universal approach in dealing with P0603 regardless of the make or model. This code requires expert intervention because of its delicate nature as it deals with the PCM. Therefore, as much as you try to save money and time through DIY, it is important to consider the state of your vehicle. As a final note, this code requires immediate attention and should be treated as soon as it is detected in a vehicle.

P0603 – What Does It Mean and How To Fix It