Every cylinder should add about the same amount of power each time it fires. When one cylinder adds much less, or much more, than the others, the engine computer notices. A P0272 code means it found that cylinder 4 is not contributing its fair share.
This code is most common on diesels. This guide explains how the computer measures each cylinder, what makes cylinder 4 weak or strong and how to find the cause.
P0272 Code Breakdown
Every OBD-II code follows the same five-character pattern set by the SAE J2012 standard. Each character narrows down which system has the fault. This table shows what each part of the code tells you.
| Character | Meaning | What It Tells You |
|---|---|---|
| P | Powertrain | The fault is in the engine or transmission systems. |
| 0 | Generic (SAE) code | The definition is the same on every OBD-II vehicle. |
| 2 | Fuel and air metering | The fault involves fuel and air metering, such as injectors, the fuel pump, throttle sensors or boost control. |
| 72 | Specific fault | Cylinder 4 Contribution/Balance Fault |
What the P0272 Code Means
The SAE J2012 standard defines the P0272 code as Cylinder 4 Contribution/Balance Fault. Each time a cylinder fires, it speeds the crankshaft up a little. The powertrain control module (PCM) watches those tiny speed changes through the crankshaft position sensor and works out how much each cylinder contributes.
On many diesels, the PCM also adjusts each injector’s fuel to keep the engine smooth at idle. These corrections are often called balance rates. A cylinder that needs a large correction, or one the PCM cannot balance at all, sets this code.
The fault is not electrical. The injector circuit can be fine while cylinder 4 still makes too little or too much power because of a worn injector, low compression or another mechanical problem.
On inline four engines, cylinder 4 is at the back, nearest the transmission. On GM and Chrysler V8s, it is second on the passenger side, and on Ford V8s it is the rear cylinder on the passenger side. Numbering varies by maker, so always confirm the layout in your service manual.
Symptoms of a Weak or Strong Cylinder 4
Symptoms are often strongest at idle. Common signs of a P0272 code include:
- Rough or shaky idle
- Check engine light on
- Misfire on cylinder 4, sometimes with P0304
- White or black smoke
- Knocking from one cylinder on diesels
- Loss of power and fuel economy
On diesels, a leaking injector can also wash fuel into the oil, raising the oil level on the dipstick. Check the oil level and smell it for fuel if you suspect an injector problem.
Most Common Causes of the P0272 Code
Fuel delivery and compression problems cause most of these codes:
- Worn or clogged injector. It delivers too little fuel or the wrong spray pattern.
- Leaking injector. It delivers too much fuel and makes the cylinder run strong.
- Low compression. Burnt valves, worn rings or a head gasket leak.
- Injector seal leak. Combustion gas leaks past the injector.
- Wiring resistance. A weak connection makes the injector open late.
- Ignition fault on gasoline engines. A weak coil or plug lowers contribution.
Tools You Will Need
You can do most of this testing at home with basic tools:
- Scan tool that shows balance rates or runs a contribution test
- Compression tester for your engine
- Leak-down tester
- Infrared thermometer for exhaust manifold runners
- Digital multimeter
How to Diagnose the P0272 Code
Start with the scan tool. Balance rates and contribution tests show whether cylinder 4 is weak or strong, which points to different causes.
Check Balance Rates or Run a Contribution Test
With the engine warm and idling, look at the balance rate for each cylinder. A cylinder needing much more fuel is weak, and one needing much less is strong. GM lists balance rate limits in its service information, often around plus or minus 4 cubic millimeters at idle on Duramax engines. Ford tools can run a cylinder contribution test.
Do a Cylinder Cutout Test
Many scan tools can shut off one injector at a time. When you cut out a healthy cylinder, idle drops noticeably. If cutting cylinder 4 barely changes the idle, that cylinder is not doing much work.
Check Compression
Run a compression test on all cylinders. Readings should be within about 10% to 15% of each other. A low reading on cylinder 4 points to valves, rings or the head gasket rather than the injector.
A leak-down test shows where the air escapes, which tells you which part has failed.
Check the Injector Return Rate on Diesels
On many common rail diesels, a return flow or leak-back test shows if an injector leaks too much fuel. Follow the service manual procedure for your engine.
Repairs That Clear the P0272 Code
Match the repair to what your tests found. Then clear the code and drive under the same conditions that set it.
- Replace the cylinder 4 injector if balance rates or leak-back tests point to it. Diesel injectors often need coding to the PCM.
- Replace injector seals if combustion gas leaks past them.
- Repair low compression such as burnt valves or a head gasket leak.
- Repair high-resistance wiring to the injector.
- Fix ignition faults on gasoline engines, such as a weak coil or worn plug.
If one diesel injector has failed from contaminated fuel, the others may not be far behind. Check the fuel filter and water separator, and test all injectors before deciding how many to replace.
Common Mistakes to Avoid
These mistakes waste money or leave the real fault in place:
- Replacing the injector without checking compression
- Ignoring fuel in the oil on a diesel
- Skipping injector coding after replacement
- Replacing all injectors when only one tests bad
Repair Cost Breakdown
The cost to fix a P0272 code depends on the cause. This table shows typical ranges for parts and labor.
| Repair | DIY Cost | Typical Shop Cost |
|---|---|---|
| Injector seals | $20 to $80 | $200 to $500 |
| Gasoline port injector | $40 to $150 | $150 to $500 |
| Diesel injector | $200 to $600 | $400 to $1,200 |
| Head gasket or valve repair | $300 to $1,000 | $1,500 to $3,500 |
Diesel injector work often costs more in labor than parts, since valve covers and fuel lines must be removed. Testing first can stop you from replacing an injector when the problem is compression.
Is It Safe to Drive with a P0272 Code?
You can usually drive gently, but do not ignore it. A leaking diesel injector can wash fuel into the oil, thin it out and damage bearings. A weak cylinder can also overheat the catalytic converter or diesel particulate filter.
If the engine knocks loudly, smokes heavily or the oil level rises, stop driving and have it inspected.
Related Codes
These codes often show up with this one or point to the same system:
| Code | Meaning |
|---|---|
| P0270 | Cylinder 4 Injector Circuit Low |
| P0271 | Cylinder 4 Injector Circuit High |
| P0304 | Cylinder 4 Misfire Detected |
| P0300 | Random/Multiple Cylinder Misfire Detected |
| P0087 | Fuel Rail/System Pressure Too Low |
Getting Cylinder 4 Back in Balance
A P0272 code means cylinder 4 contributes too little or too much power compared with the others. Worn or leaking injectors and low compression cause most cases.
- Check balance rates or run a contribution test.
- Do a cylinder cutout test.
- Run compression and leak-down tests.
- Test injector return flow on diesels.
Frequently Asked Questions
Does the P0272 Code Mean the Injector Is Bad?
Often, but not always. A weak injector is the most common cause on diesels, but low compression gives the same result. Run a compression test before replacing the injector, since a new injector will not fix a burnt valve.
What Are Injector Balance Rates?
Balance rates show how much the PCM adds or removes fuel from each injector to keep the engine smooth at idle. A cylinder with a large positive rate is weak, and one with a large negative rate is strong. They are a quick way to spot a problem injector.
Can a Gas Engine Set This Code?
Yes, though it is more common on diesels. On gasoline engines, the PCM can measure each cylinder’s contribution through crankshaft speed. Ignition faults, vacuum leaks and clogged injectors can all lower one cylinder’s contribution.
Can Bad Fuel Cause a Balance Fault?
Yes. Water, debris and poor-quality fuel wear injector nozzles and valves, which changes how much fuel each one delivers. Drain the water separator, replace the fuel filter on schedule and buy diesel from busy stations to lower the risk.
Do New Diesel Injectors Need Programming?
Many do. Modern diesel injectors often come with a code printed on them that tells the engine computer how that injector flows. A scan tool enters the code after installation so the PCM can balance the engine correctly.