What Does the Engine Code P0603 Mean?

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A P0603 code means that your vehicle’s Powertrain Control Module (PCM) has registered an unexpected error in its Keep Alive Memory (KAM). Your car or truck’s Powertrain Control Module continually runs diagnostic tests on a variety of key functions, including your anti-lock brakes and transmission. The KAM stores the results of these diagnostics.  A P0603 error indicates the KAM has registered a failed self-test.
While the Diagnostic Trouble Codes (DTCs) indicate a problem with your engine, you may need an OBD-II code reader to interpret what the problem is. Keep in mind that you will likely need the help of an expert to identify the specific cause(s) of a P0603 engine code.
Fortunately, car insurance app Jerry has put together this guide for what a P0603 might mean, what to do about it, and how to fix your car and be on your way. 
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What does the engine code P0603 mean?

This code indicates a problem with your vehicle’s Powertrain Control Module (PCM)’s computer system—specifically its Keep Alive Memory (KAM). The problem may simply involve a problem with your car’s battery not sending enough power to the KAM, but it may be more involved.

How much will it cost to fix?

While many problems can be diagnosed in about an hour (and repair shops typically charge $75-150/hour), a P0603 error may take longer to isolate. This is because it may signal a problem with your car’s wiring system.
If your problem is a bad battery, a professional will likely charge between $186-222 to replace the battery, depending upon your vehicle’s make and model. If your PCM is bad, this will likely cost you around $1,000.

What can cause the P0603 engine code?

Some common causes include:
  • Problems with your vehicle’s battery or battery terminal connection
  • Bad power supply to your Powertrain Control Module (PCM) or Engine Control Module (ECM) 
  • Software problem with either ECM or PCM
  • Defective PCM

Common symptoms of the P0603 engine code

Drivers will likely notice the following symptoms:
  • Engine light is on
  • ABS/traction control light is on
  • Service engine soon light is on
  • Vehicle stalls
  • Erratic shifting
  • Engine misfires
  • Failed emission inspection
  • Problems starting

How serious is the P0603 code?

This code may indicate a simple problem with your battery or it may signal a serious problem with your car or truck’s Powertrain Control Module (PCM). Because the P0603 code indicates a problem with your vehicle’s Powertrain Control Module—essentially your car’s “brain”—it is important to diagnose the problem as soon as possible. It may mean a simple fix, but it may also indicate a problem with the car’s main computer.

Can I fix the P0603 engine code myself?

While complex problems will require a professional, if you get a P0603 code, you can easily check for some common issues with your vehicle’s battery.

Check your battery voltage

Sometimes your battery is not supplying enough power to the PCM. Using a multimeter, check your battery. If the voltage is below 12 volts with the engine off—or under 14 volts with the engine idling—then charge the battery (or replace it if the battery is more than 4 years old). 
Reset the code and see whether the P0603 code shows up again after a few days of driving.

Check your battery contacts

Also, inspect your battery contacts. Corroded or dirty contacts can cause your battery not to charge properly.

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