8 Reasons For P1222 Cummins Code and Fixes!

The P1222 code in Cummins is a diagnostic trouble code. It comes on when the Engine Control Module ECM senses an error in the fuel injection system. This is applicable for  5.9L Cummins engines from 2003 to 2007. 

While driving your Cummins truck suddenly you hear an incessant chiming noise and then the wait to start WTS light comes on. To get to the heart of the matter you hook your car to an on-board diagnostic OBD II sensor and it shows P1222 Diagnostic Trouble Code DTC code. 

So, you wonder what is P1222 Cummins Code?

Knowing the problem is just the preliminary part of the fix. Now we will walk you through the possible reasons and solutions. Keep reading to get to the nitty gritty of this DTC code. 

What Does P1222 Code Mean?

P1222 code on Cummins means the ECM (Engine Control Module) detects excessive injector return flow. This diagnostic trouble code (DTC) code will appear in the OBD II sensor for 5.9 L Cummins 03-07 engines. (1)

This Cummins engine has a high-pressure common rail fuel injection system that runs with a bosch injection pump. During the fuel injection from a common rail under high pressure, ECM controls the fuel injection start, quantity, and time.  

P1222 code translates as “leak detected during motoring”.  This “leak” is when the ECM detects more than expected fuel flow in the injection system. After the leak detection, ECM tries to counter it to a predetermined limit. After this limit is reached, ECM enables engine derate. 


P1222 code on Cummins appears when ECM notices there is excessive fuel flow in the fuel injection system. 

8 Possible Reasons And Solutions To P1222 Cummins Code 

Here is a brief table outlining all the possible reasons, solutions and symptoms that come with them. (2)

Reason Solutions
Throttle pedal IssueReplace the sensor 
ECM ProblemReprogram ECM
Water contaminationPrevent contamination 
Faulty Fuel rail pressure sensor Replace the sensor 
Fuel supply issue Check lift pump and fuel filter 
Valve Issues Fix Cascade overflow valve and pressure limit valve

Now that you have an overall idea about where to look, we will go through each reason and solution with detailed procedures. 

Reason 1: Throttle Pedal Issue 

The throttle pedal position sensor controls the amount of airflow into the engine. If this sensor is faulty then the P1222 DTC code might appear in your OBD scan. However, TPS sensors cause another fault code P1514 as well. 


Here are the symptoms to look out for in a faulty throttle pedal position sensor. 

  1. Check Engine Light ON 
  2. Trouble accelerating 
  3. Engine stalling 
  4. Increased fuel consumption 
  5. Vehicle goes to “Limp Mode”


Follow these steps to fix a faulty TSP sensor.

Step 1: Visually inspect the sensor for mechanical damage located on the pedal. 

Step 2: Check the wirings and electric connections and fix if it’s loose or disconnected. 

Step 3: Re-program the TPS sensor if there is no visible damage

Step 4: Replace the TPS sensor if all three steps above don’t work 

It costs around $110-$200 to replace a throttle position sensor including the labor charge. (2)

Maintenance Guide 

Clean the TPS sensor with a throttle body cleaner every 30,000 miles. Remove dirt around the sensor and make sure the sensor is dry after cleaning. Don’t use too much cleaning agent and use a towel to wipe it afterward. 

Reason 2:  ECM Problem 

A lot of Cummins owners have complained about a bug in their ECM. This bug can be one of the reasons for this DTC P1222 code. To fix this bug, reprogram your ECM. 


Some common symptoms of bad ECM are:

  1. Check engine light On 
  2. Engine misfire 
  3. Poor engine performance 

Showing DTC code P1222 without actual fuel injection issue shows that your ECM needs reprogramming. 


Here’s how you can Reprogram your ECM 

Usually, it is recommended to reprogram PCM at a dealership. However, if you want to do it on your own, follow the below process.

Tools Required 

  • PCM Scanner 
  • PCM software
  • Computer 

To get the exact PCM scan tool and software, contact your local dealer. 


  1. Download the PCM software on your computer. 
  2. Connect the scan tool to your computer
  3. Make sure your battery is fully charged. Start the software program and enter your vehicle information. You might need your vehicle’s VIN number as well. 
  4. After the data is transferred to the scanner, disconnect the scan tool. 
  5. Locate your truck’s PCM. Usually, it can be found near the battery. 
  6. Find the OBD II connector on PCM and connect it with the scan tool. 
  7. Start your truck ignition. 
  8. Turn the scan tool “ON”.
  9. Key-in vehicle information and start the transfer
  10. The scan tool will alert when the transfer is complete
  11. Disconnect the scan tool from the OBD II connector 
  12. Turn off your truck’s engine
  13. Start the truck again to check if the engine check light is still on or not. 

Maintenance Guide

Check for loose wirings in your ECM and clean dirt and debris after visual inspection. At the same time, make sure you don’t operate your engine in extreme weather for a long time. 

Reason 3: Water Contamination

If there is rust accumulated on the FCA (fuel control actuator), this means there has been water contamination in the fuel system. 


  1. Engine Jerking 
  2. Trouble accelerating 
  3. Visible rust on the FCA (fuel control actuator)


Use a fuel additive to remove water from the gas tank. Make sure you get fuel additives that have isopropanol in them. If you are using ISO HEET fuel additive then apply one 12-ounce bottle for 20 gallons of fuel. 

However, if there is more water in your gas tank than fuel then fuel additives won’t be effective. In that case, drain all the fuel from your tank and refill it with good-quality fuel. 

Maintenance Guide

Use good quality Diesel in your Cummins. Look out for leaks in the engine tank. 

Use fuel testing to monitor contamination levels. Follow a comprehensive fuel conditioning program for optimal performance. (3)

Reason 4: Faulty Fuel Rail Pressure Sensor 

This sensor is designed to moderate the fuel pressure in a common rail fuel injection system. Anything wrong with this sensor will result in a DTC code P1222. 


  • Your Check engine light will be turned on and will stay that way until you resolve this DTC 
  • Reduced engine efficiency 


You need to replace your fuel rail pressure sensor if it’s faulty. It is a crucial part of the injection system and the engine won’t start if this part is malfunctioning. 

Here’s how to replace your fuel pressure sensor (4)

Step 1: Release fuel pressure by pushing on Schrader valve 

Step 2: Disconnect the battery 

Step 3: Remove mounting hardware and then remove the faulty sensor 

Step 4: Install the new sensor 

Step 5: Plug in the battery 

Step 6: Test drive your vehicle to check if everything is working properly.

It will cost you $200 to $340 to replace this sensor including labor costs depending on your engine. (5)

Maintenance Guide 

Make sure your fuel rail pressure sensor is not exposed to dirt and pollutants for a prolonged period of time. 

Reason 5: Fuel Supply Issue 

When there is an issue with the lift pump in your Cummins, the fuel supply will be affected. Similarly, a clogged fuel filter will hurt your fuel supply pressure. 


Bad fuel filter will make your engine perform badly with a rough idle. Similarly, a faulty lift pump will cause high fuel consumption and blue/ black smoke will come out. It is best to replace your lift pump rather than repair it. 


Follow these methods to get the perfect fuel supply 

Step 1: Clean the clogged fuel filter. Follow this guide 

  1. Relieve pressure from your fuel system by removing the fuel pump fuse. Then turn on the engine and run it for 1 or 2 minutes. 
  2. Turn off your car and unplug the negative terminal of your battery. 
  3. Put a pan exactly underneath the filter then remove all the connections of the fuel filter. 
  4. Remove the filter from the bracket or bolt. Tap gently on both nozzles of the fuel filter to remove gas. 
  5. Use a pressurized carburetor cleaner and attach it to the nozzle on the fuel filter. 
  6. Then thoroughly spray inside the fuel filter. 
  7. After that tap on the filter to remove debris and air dry it for an hour. 
  8. Finally reinstall the fuel filter. 

Step 2: Replace the fuel filter if cleaning the fuel filter didn’t fix it

Step 3: Repair loose connection/ wiring of the lift pump

Step 4: Replace the lift pump if it shows severe signs 

You should be able to replace your lift pump with around $150 while fuel filter replacement costs $100-$200. 

Maintenance Guide 

Replace your fuel filter every 10,000 to 25,000 miles. (6)

Reason 6: Valve Issues

There are two fuel supply valves: a cascade valve and a pressure limit valve. A pressure limit valve regulates the common rail fuel pressure. When a pressure limiting valve leaks out return fuel then P1222 might appear. 

Then there is the Cascade valve that regulates fuel pressure and helps lubricate moving parts. Failure of the cascade valve will result in P1222 DTC as well. 


Symptoms of valve issues are similar to those previously mentioned


If your cascade overflow valve fails, you must replace it. Get a mechanic to do it and the valve costs around $30. (7)

Replace the pressure limiting/ pressure relief valve if it’s leaking. This relief valve costs around $20 and we recommend you get it done by an expert mechanic. (8)

Maintenance Guide 

You must inspect your Pressure relief valve at least once a year for visible damage. 

Reason 7: Fuel Injector Issue

Faulty fuel injector, open fuel injector harness, and poor electric connections in fuel injector circuits, all lead to a P1222 DTC code. 


Symptoms of fuel injector issues are similar to those previously mentioned


Here’s what you can do to fix all your fuel injector issues.

  • Plug the Open Harness: The fuel injector harness connects to the main harness through the injector connector. If this harness connection is open, you need to plug it in.
  • Fix electric connections: Check for poor electric connection of the injector. Fix all the electric wirings and connections accordingly. Tighten the loose connections. 
  • Replace Fuel Injector: Since fuel injectors fail due to mechanical issues, it is not recommended to clean them. Driving with bad fuel injectors can cause serious damage to the engine so you must replace it. 

Maintenance Guide 

Replace your fuel injector every 200,000 km to 300,000 km for your Cummins. However, for replacement, it will cost you around $350 including the service charge.(9)

Reason 8: Weak Injection Pump (CP3)

A bad/weak injector pump will disrupt the fuel flow into the combustion chamber. Dirt, pollutants, and water can contaminate the injector pump. Dirty fuel, too little fuel, and disruption in injector timing will cause a CP3 to fail as well. (10)


Symptoms of a weak injection pump are similar to those previously mentioned.


Since the fuel injector pump is an expensive part, we recommend repairing it. However, this repair should be done by an expert mechanic and will cost you around $300. (11)

If your high pressure injector pump is beyond repair, then replace it with a new one. It will cost you $1700-$2400 including the labor charge. An expert mechanic needs approximately 5 hours to replace an injection pump. 

However, if you want to replace the fuel injector pump yourself, this video might come in handy.

Maintenance Guide 

Replace your Cummins injector pump every 100,000+ miles. To prevent premature failure of the injector pump, use good-quality diesel. At the same time, regularly replace your fuel filter. 

What If You Don’t Fix the P1222 Code at All?

If you don’t fix the P1222 code, your engine will suffer in the long run. Some users mentioned that they could not shift gears at all. Neglecting this issue will harm your engine and possibly damage engine parts. 

How Long Can You Drive with  P1222 Cummins Code?

You can drive with the P1222 Cummins code to the next gas station or mechanic shop. P1222 code does not need to be fixed immediately. When this code comes on, check for other fuel-related codes. If there are any, fix them first. 

However, P1222 signals an array of issues related to many engine parts. Some of them are integral for engine running. Also, this code will make your engine go into limp mode. This means until you fix it, your car would run on half the power. 

Similarly, you will notice difficulty accelerating, engine stalling, high fuel consumption, engine stalling, jerking, difficulty changing gears, etc. So, unless absolutely necessary we don’t recommend driving with a P1222 code on your Cummins. 


We don’t recommend driving with this code. The WTS light is an indicator that you should stop your vehicle and fix the DTC first. 

Bottom Line 

We hope this article helped you track down your specific reason for the P1222 Cummins code and fix it without much hassle. Leave us a comment to notify us of your Cummins confusions and we will try to clear the air. 

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William Baldwin

This Is William Baldwin, The Founder & Managing Editor of this website. Me and my team share automotive tips, tricks, and news

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Talha Atta

Talha Atta, a Mechanical Engineer and experienced technical content writer and editor at Autoglobes.com with a passion for the automotive industry.