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P0603 Code on 7.3 Powerstroke: Meaning & How To Fix

The 7.3 Powerstroke is a great engine produced by Ford in the mid-90s up to the mid-00s. While there are many pros of this engine, it’s known to show the P0603 error code when plugged into an OBD2 scanner. 

The P0603 code means there is an error in the PCM (Powertrain Control Module) of the car because it failed its KAM (Keep Alive Memory) test. This module controls the engine, transmission, and other parts of the car based on sensors, so the error code has many potential meanings and fixes. 

Read on to learn more about the P0603 code and how to fix it on your 7.3 Powerstroke. 

What Does a P0603 Error Code Mean?

The P0603 code denotes an error in the powertrain control module of a vehicle. The range of problems that could show this code is very wide, and older cars like those with the 7.3 Powerstroke are more likely to have serious problems when they show this code.

As such, if you encounter this code, take your car to a professional or fix it yourself (if you’re capable) immediately. 

Understanding PCM and KAM

The powertrain control module is the computer responsible for tweaking settings regarding drive cycles and other settings based on input from various sensors around your car’s powertrain. During the manufacturing process, the PCM is configured with settings that are specific to the 7.3 Powerstroke. 

Over time, the PCM makes hundreds of small changes to these settings to improve performance. These changes are based on the model, your driving practices, and weather conditions. To facilitate faster recovery of the recorded data, the PCM stores this information in the KAM. 

The KAM (Keep Alive Memory) is a volatile RAM designed so that it doesn’t get cleared when you turn off your vehicle. As such, the data that the PCM stores in the KAM stay between drives. To test access to this data, the PCM performs a KAM test. Failing this test will lead to the registration of a P0603 error by the vehicle. 

Symptoms Indicating Probable P0603

To see the P0603 code, you would need to scan your car using an OBD2 scanner (or OBD scanner for older models). Some symptoms might indicate this error code, so it’s a good idea to keep an eye out for them.

Learning to spot these signs is just as useful as detecting the symptoms of ICP Sensor Failure—it would help greatly in the diagnosis. Regardless of the symptoms, you’ll probably see the check engine light. 

Just know that this particular dashboard light shows up for various reasons and is not confined to this error code. If you see the check engine light, you generally need to do some more digging using the OBD scanner to get an accurate diagnosis. 

Here are a few known symptoms of an engine that will probably show the P0603 error code when you plug it into an OBD scanner. 

1. Shaking While Idling

You might notice that your car is a little too shaky when you’re at a stop light or any other time you’re idling. If you scan that vehicle on an OBD2 scanner, there is a high possibility that you will get a P0603 in response. This could be due to a faulty Keep Alive Memory module or a problem with the PCM

2. Engine Issues: Stalling, Misfiring, Stumbling

While a malfunctioning PCM isn’t the only possible reason for a stalling engine, there are several reasons it could be the culprit. The PCM controls several systems in your vehicle that potentially lead to stalling. Settings regarding ignition, engine timing, ABS, and even transmission are stored in the KAM. 

Any malfunction in those systems could lead to a stalling engine and, thus, a P0603 error code. If you find that your engine is stalling, take the car for a check-up immediately. 

Additionally, other problems with your engine, such as misfires and frequent stumbling, can be a symptom of a malfunctioning PCM. 

3. Poor Fuel Economy

After driving your vehicle for some time, you should have a rough idea of how much fuel it typically uses. That is, you should know how many miles per gallon (or kilometers per liter) you are getting when driving. If you find that your car is suddenly using up more fuel than usual, it’s advisable to take the vehicle for a check-up. 

The engine control unit (ECU) – also known as the engine control module (ECM) – is a micro-computer responsible for controlling fuel injection into the engine and spark ignition. The PCM saves data about this unit, and when it malfunctions, the dashboard computer registers the P0603 error. 

A malfunction in the ECU likely leads to inefficient gas mileage. You can notice if your vehicle’s fuel consumption has increased if you need to fill up the tank more often despite driving similar distances. 

Possible Causes of P0603 Error Code

There are two generalized causes of the P0603 error code registration: electrical issues and problems in the PCM.

Let’s take a look at each:

1. Electrical Issues

There are several issues in the electrical system that could prevent the PCM from passing its KAM test. This includes a dead or malfunctioning battery, charging system problems, or faulty wiring

Problems in the PCM ground circuit (such as short circuits) can also prevent the test from reaching completion. As a vehicle ages, the lifespan of its electrical circuits inevitably reaches its end, and you can expect malfunctions. 

Additionally, as different parts of a vehicle are replaced or fixed, there is an increased likelihood of damage to the electrical circuits. 

2. Malfunctioning PCM

Any malfunction in the powertrain control module or the Keep Alive Memory can cause the P0603 to register. This includes:

  • Water damage 
  • Old software
  • Corroded battery terminals
  • Incorrect installation

How To Fix P0603 Code on 7.3 Powerstroke

It’s important to note that the P0603 error code is generic. That means that you can get the same code for multiple engines on a wide variety of vehicles for several reasons. Fixing the problem depends on the specific diagnosis and the make and model of the car. 

If you are not confident about opening up and fixing your car on your own, I highly suggest hiring a professional auto electrician. Connecting the wiring incorrectly could lead to bigger problems than the P0603 code. 

Here are steps you can take to fix this error on a 7.3 Powerstroke.

1. Clean Up Electrical Connections

The first thing you should do is clean up any corrosion in the battery terminals or wiring. Make sure that all electrical connections are secure. You should also remove and replace any wires that look too old or frayed. 

Take the time to go through the entire electrical circuit, or hire an auto electrician to do this check-up.

2. Replace Faulty Parts

Depending on which parts are causing the malfunction in your vehicle, you should remove and replace them. Check the battery and replace it if it is dead or damaged beyond repair. 

You might also need to replace your PCM if you think it’s broken.

Here’s how to do that:

  1. Ensure your car is switched off, and take the key out of the ignition.
  2. Locate the PCM. It’s usually under the parking brake, but you may need to consult the owner’s manual of your car. 
  3. Disconnect the PCM, taking note of its chip code.
  4. Purchase a new compatible PCM (with the same chip code). 
  5. Connect the new PCM in place of the old.

Note: In some models, you may find the PCM under the passenger seat, behind kick panels, or even under the floorboard. The only definitive way to know exactly where to look is to consult the owner’s manual.  

3. Remove After-Market Chips

Given the age of your vehicle, it is understandable if more than a few parts have been replaced over the years. You’ve probably got a few after-market chips installed, which aren’t always manufactured or configured correctly. 

Try taking out any after-market chips installed in your vehicle and check if the error code resolves by itself. If you have several chips installed, it is best to take them out one by one and run the scanner after each. This way, you should be able to pinpoint which chips need replacement. 

4. Update Software

As you would do with any other computer, updating the software on your PCM will give it a chance to automatically reconfigure any errors.

Needless to say, this fix will not work if the issue is caused by physical problems such as corroded battery terminals or frayed wire connections. 

Final Thoughts

The P0603 error code is a common diagnostic result for 7.3 Powerstroke engines. It’s probably caused by a fault in the powertrain control module where a standard testing procedure fails to reach completion. 

Using the four fixes mentioned above, you should be able to troubleshoot and fix the problem easily. Take your vehicle to a professional if you are hesitant to fix it yourself.