what is p0603

What is the P0603 code on a 7.3 Powerstroke? [Meaning, Causes & Fix]

The Ford 7.3 Powerstroke engine relies on the Powertrain Control Module (PCM) to control many of its essential engine systems. 

These include ignition, timing, turbo boost pressure, throttle position, cruise control, air and fuel mixtures, transmission, and ABS.

The Keep Alive Memory (KAM) stores vital information about these systems, and the P0603 code tends to occur whenever the PCM isn’t able to reach this information stored in the KAM. 

This happens either because the KAM itself has failed, the PCM has failed, or there are issues with the car’s electrical systems.

To fix this problem, you will first need to diagnose a few of the car’s components, such as the battery, the PCM, and a bunch of wires. When you eventually do find the culprit, you will need to either update or replace certain components. 

The P0603 code is indeed a serious one, which means that it can affect the car’s driveability. You should not drive the car until you resolve it completely. 

If you have adequate experience working on delicate components such as the PCM, you can solve this problem yourself.

Lastly, the prices linked with solving these issues are highly dependent on what actually needs fixing. 

A best-case scenario involves spending a few dozen bucks on a new wire while worst-case scenarios will require you to spend upwards of $1,000 on a new PCM. 

What does the P0603 code mean on a 7.3L Powerstroke?

The P0603 code refers to a problem where the PCM has failed to read vital systems information from its own KAM system. 

The KAM stores various information about the inner workings of an engine in order to reach optimal efficiency, power, emissions, and sophistication. 

Common Symptoms of the P0603 Code on a 7.3 Powerstroke 

The P0603 fault code will be accompanied by the following symptoms: 

  1. Check Engine Light Is On
  2. Engine Stalling Issues
  3. Engine Has Difficulty Starting
  4. Rough Idling and Acceleration
  5. Badly-timed Shifting
  6. Engine Misfires
  7. Dramatically Increased Fuel Consumption

Check Engine Light Is On


Virtually all notable engine issues either start or finish with the dreaded Check Engine Light, and the P0603 code is no different.

As such, if you come across the CEL, be sure to look for further symptoms listed in this article.

Engine Stalling Issues

The KAM is tasked with providing the right software data for optimum engine operation, such as air and fuel mixtures. If such software can’t be reached, it can cause the engine to stall intermittently.

Stalling can happen both on idle and while accelerating, which means that it is sure to make your daily driving experience much worse.

Engine Has Difficulty Starting

Among other things, the KAM stores information about timing and ignition, which need to be at least adequate for your engine to kick to life. 

Sometimes, the discrepancies can be so severe that they could cause your engine to fail to start completely.

There are many potential reasons why an engine won’t start, so it’s essential to also look for other symptoms listed in this article. 

Rough Idling and Acceleration

The KAM also stores vital information about fueling the engine, which means that the KAM knows when to add more fuel and wants to back it off a little. 

If the PCM isn’t able to reach that data, it won’t be able to properly regulate the optimum mixtures which will lead to rough idling and subpar acceleration.

You will feel your car’s power delivery being weirdly inconsistent and not representative of the amount of throttle input while your RPMs are going to go up and down. 

Badly-Timed Shifting 

Various transmission-related information is stored in the KAM. This includes stuff like all the lifelong transmission resets, software updates during the car’s life, and specific values added along the way for improved shifting, efficiency, gearing, and power delivery. 

If you take the KAM out of the equation, you are essentially robbing your transmission of all the information added to make it better. 

So, if your transmission starts shifting badly, the KAM could very easily be the reason why. 

Engine Misfires

Properly diagnosing the reason behind a misfiring engine is rather difficult as there are many potential reasons why. 

However, in this case, engine misfiring is usually caused by timing issues, but can also be caused by ignition problems, fueling, and air management issues. 

All of these systems are controlled by the PCM via the info the KAM provides which means that if the KAM fails, your engine is likely to misfire. 


Dramatically Increased Fuel Consumption

Last but not least, if you notice your fuel consumption has gone haywire, be sure to check the car’s fuel injectors and fuel filters.

If the issue persists, you should also focus your attention on the KAM, which holds information about the efficient fueling of the engine. 

Understandably, if the PCM can’t get ahold of that information, your fuel efficiency is sure to suffer.

What issues cause code P0603 on a 7.3 Powerstroke?

The following issues cause the P0603 code on a 7.3 Powerstroke: 

  • KAM is Not Receiving Enough Power
  • Battery or KAM Has Shorted Out
  • Loose Connection & Battery Terminal Corrosion
  • Malfunctioning Wiring Of KAM & Keep Alive Power (KAPWR)
  • Damaged KAM or Powertrain Control Module 
  • PCM Internal Fault Due to Water Intrusion 
  • Faulty Battery & Charging System
  • Outdated PCM Software

How serious is the code P0603 on a 7.3 Powerstroke?

The severity of the P0603 is fairly relative, but in order not to risk it, we are going to conclude that the P0603 code is indeed really serious.

As such, you should simply avoid driving the car when you diagnose the P0603 code as the problems can only get worse, even if they seem mild at the start. 

The reality is that the problems can range from minor trouble such as slightly worse fuel efficiency all the way up to crippling issues with the car’s power delivery or an engine that fails to start up completely.

Moreover, if something is indeed really wrong with the KAM, it is bound to get worse over time, which means that the sheer number of symptoms is likely to increase while the severity of each becomes more and more aggressive.

How to Fix P0603 Error Code on 7.3L Powerstroke

Before trying to fix the P0603 code, you need to make sure you got all the right tools for the job. These are

  • OBD-II Scanner
  • Voltmeter
  • Battery Charger
  • Hand Tools (Screwdrivers, wrenches, pliers…)
  • Vehicle Owner’s Manual/ Vehicle Repair Manual
  • A Flashlight 

After gathering the right equipment, proceed to solve the P0603 code.

Wait Or Remove Aftermarket Engine Management Products

As all of these recommendations, guides, and instructions tend to regard a non-modified 7.3L Powerstroke, the first thing you need to do is to remove all the aftermarket engine products such as tuning chips or various ECU remaps.

These do affect the same systems that are usually stored in the KAM, which means that sometimes, the problem can be solved simply by removing these. 

Sometimes, the code itself will go away after a few days with these aftermarket products, but often, you will have to either clean the code manually after making sure it’s only due to chip tuning. 

Check Your Battery Health

Sometimes the KAM system is actually working perfectly, but the only problem is that it does not get enough juice from the battery.

This means that you will have to test out the battery with a battery charger. Go ahead and charge up the battery fully, clear the code with an OBD-II scanner, and try to drive the car normally for a week or two.

If the P0603 code reapers after a week or two weeks, there is a good bit of chance that your battery simply does not have enough juice to power it. 

If your battery is old and needs to be replaced, be sure to do so soon enough as a weak battery can cause various other problems as well. After replacing it, the P0603 code should go away permanently. 

Inspect Battery-Related Wiring 

After inspecting the battery, you should immediately go ahead and inspect all the wiring that goes to and from the battery, especially those that power the PCM itself. 

Look for any signs of loose connections and try to wiggle the cables in place if needed. If some of them look damaged, heavily scuffed, or torn, you should replace these immediately and test out the battery and the wiring once more.

Also, look for signs of corrosion on the wiring and the battery terminals, and go ahead and clean it all off using industry-grade battery corrosion cleaners with the battery safely unplugged from the car. 

Check For PCM Wiring Leakage 

If the PCM isn’t getting enough juice, it is not going to be able to extract the necessary information from the KAM. This means that you will have to test out the power lines that flow from the battery to the PCM housing. 

Get ahold of a voltmeter, stick it onto the wires, and look for consistent 12.5V readings.

It’s also a good idea to wiggle the wires a little bit while doing this test just to see if any of that is going to affect the readings.

If it indeed does affect it, or if the voltage can’t seem to stay consistent, you will need to replace the power supply and try once more. 

Update to the Latest PCM Software Version

The Powertrain Control Module software gets updated a few times during a car’s lifespan. These are typically done to either solve specific problems, make the car more efficient, or make various other systems compatible with each other.

If you run your PCM on outdated software, you could very easily end up with a P0603 fault code.

Be sure to visit your local dealer and update the PCM to its latest settings, if you are lucky enough, the P0603 code is going to go away on its own.

However, if the simple update does not help and if the PCM seems to be malfunctioning, you will have to replace it.

When replacing the PCM, it is important to ensure that the new module is programmed correctly and is compatible with the vehicle’s make and model. 
This is typically done by a professional mechanic or dealership technician using specialized software and equipment.

How much does the DTC P0603 cost to solve?

The costs to solve the P0603 code depend on what needs doing. You should consult the table below for a general assessment of the final costs.

New Wiring$30 to $80
Dealership PCM Software Update$80 to $150 (free under warranty)
A New PCM$500 to $1500

These prices do not include labor costs, which can vary from state to state.

Common Mistakes to Avoid While Solving the P0603 Code

Knowing what not to do is as important as knowing what you need to do if you want to solve the P0603 or any other code for that matter.

Therefore, make sure to pay close attention to avoiding these common mistakes:

  • Reading the Voltage Wrong While Testing Power Supply Lines
  • Not Testing Everything (Connectors, Terminals, Harnesses, Wirings) Before Potentially Replacing the PCM