P0273 Cylinder 5 Injector Circuit Low

P0273 is a diagnostic trouble code (DTC) that means the engine control module (ECM/PCM) has detected an abnormally low electrical condition in the fuel injector circuit for cylinder #5.

The word “Low” refers to the electrical condition of the injector circuit. It does not necessarily mean low fuel pressure, low fuel flow, or a clogged injector.

P0273 therefore does not automatically mean that the cylinder #5 injector needs to be replaced. The injector itself may be faulty, but the problem can also be caused by the injector connector, wiring, power supply, control circuit, or ECM injector driver.

What Does P0273 Mean?

The ECM controls the fuel injector for cylinder #5 by switching its electrical circuit on and off at precisely calculated times.

When the ECM monitors the circuit and detects an electrical condition below the expected range, it can store P0273 – Cylinder 5 Injector Circuit Low.

The exact circuit arrangement varies between vehicles. Some engines use a shared power supply for several injectors, while the ECM individually controls the injector circuits. Modern diesel systems can use considerably more complex injector control strategies.

For this reason, the correct wiring diagram and manufacturer-specific diagnostic procedure are essential.

What Does “Circuit Low” Mean?

“Circuit Low” is an electrical term.

It does not automatically mean:

• Low fuel pressure

• Low fuel volume

• Low injector flow

• Lean air-fuel mixture

• Clogged injector

• Empty fuel tank

• Injector stuck closed

For example, a control wire shorted to ground can cause the ECM to see a low electrical condition even when fuel pressure is perfectly normal.

Likewise, an internal electrical failure inside the injector can produce P0273.

Where Is Cylinder #5?

The physical location of cylinder #5 depends on the engine manufacturer.

Cylinder numbering is not universal.

This is especially important on V6, V8, V10 and V12 engines because manufacturers can use different cylinder numbering arrangements.

Before testing the cylinder #5 injector, confirm its exact location using the service information for that specific engine.

Common Causes of P0273

Faulty cylinder #5 injector

The injector itself can have an internal electrical problem.

Possible failures include:

• Internal short circuit

• Damaged injector coil or solenoid

• Abnormal internal resistance

• Internal electrical failure

• Mechanical failure combined with an electrical fault

An injector may still appear physically normal while its electrical characteristics are outside the expected range.

Damaged injector wiring

The wiring between the ECM and cylinder #5 injector can cause P0273.

Possible wiring faults include:

• Short to ground

• Broken conductor

• Excessive resistance

• Damaged insulation

• Chafing

• Heat damage

• Corrosion

• Intermittent connection

A harness can look fine externally while having a damaged conductor internally.

Poor injector connector

The connector should be inspected carefully for:

• Corrosion

• Loose terminals

• Bent pins

• Poor terminal tension

• Water contamination

• Oil contamination

• Damaged locking mechanism

• Terminals pushed backward inside the connector

An intermittent connector can produce a fault that appears only when the engine is vibrating or the harness is moving.

Injector power supply problem

Some engines use a common power supply for multiple injectors.

A fuse, relay, wiring connection or power-distribution problem can therefore affect injector operation.

If several injector circuit codes appear together, investigate the shared power supply before assuming that multiple injectors have independently failed.

Short to ground

A damaged control wire that contacts the engine or chassis can pull the injector circuit lower than expected.

This can produce the electrical “Low” condition reported by P0273.

ECM/PCM injector driver problem

The ECM contains electronic drivers responsible for controlling the injectors.

A damaged driver can cause abnormal injector circuit operation.

However, the ECM should generally be considered only after the injector, connector, wiring, power supply and grounds have been properly tested.

Symptoms of P0273

The symptoms depend on how severely cylinder #5's injector operation is affected.

Possible symptoms include:

• Check Engine Light

• Rough idle

• Engine vibration

• Misfire

• Hesitation

• Poor acceleration

• Reduced engine power

• Uneven engine operation

• Increased fuel consumption

• Hard starting

• Stalling

• Increased exhaust emissions

• Smoke on some diesel engines

If the injector stops operating completely, cylinder #5 may contribute very little or nothing to engine power.

Can P0273 Cause a Misfire?

Yes.

If the cylinder #5 injector cannot deliver the correct amount of fuel, combustion may become weak or disappear completely.

The ECM can then detect a cylinder #5 misfire in addition to P0273.

For example, a shorted injector control circuit may prevent the injector from being controlled correctly. The resulting fueling problem can cause rough running and misfire.

However, the presence of a misfire does not prove that the injector itself is defective. The electrical circuit must still be tested.

P0273 Is Not a Low Fuel Pressure Code

The word “Low” can easily be misunderstood.

P0273 does not mean that the engine has low fuel pressure.

An engine can have completely normal fuel rail pressure and still store P0273 because the electrical circuit controlling cylinder #5's injector is abnormal.

Conversely, low fuel pressure can cause poor combustion without necessarily producing P0273.

Fuel pressure should therefore be checked separately when the symptoms or other diagnostic information indicate a possible fuel-system problem.

How to Diagnose P0273

A systematic electrical diagnosis is the best approach.

1. Scan for all DTCs

Do not diagnose P0273 in isolation.

Check for additional codes involving:

• Other injector circuits

• Cylinder #5 misfire

• Fuel pressure

• ECM power supply

• Battery voltage

• Camshaft position

• Crankshaft position

• Engine synchronization

Freeze-frame data can show the engine speed, load and temperature when the fault was detected.

2. Inspect the cylinder #5 injector connector

Check the connector carefully for corrosion, loose terminals, contamination and physical damage.

Terminal tension is important. A connector can look clean but still have poor electrical contact.

3. Inspect the wiring

Follow the injector harness toward the ECM.

Look for:

• Chafed insulation

• Broken wires

• Melted sections

• Pinched harnesses

• Previous repairs

• Contact with hot engine components

• Contact with moving components

Pay particular attention to areas where engine vibration can move the harness.

4. Verify injector power supply

Determine how the particular vehicle supplies power to the injector.

If several injectors share a power circuit, compare the cylinder #5 injector with another known-good injector.

A missing common supply can make several injectors appear faulty when the real problem is a fuse, relay or wiring connection.

5. Test the control circuit

The injector control circuit should be tested according to the manufacturer's wiring diagram.

Depending on the system, this can include:

• Continuity testing

• Resistance testing

• Voltage-drop testing

• Short-to-ground testing

• Short-to-power testing

• Oscilloscope waveform analysis

A simple continuity test is not always sufficient. A wire can have continuity while still having excessive resistance or failing under vibration.

6. Test the injector

The injector's electrical characteristics should be compared with manufacturer specifications.

Depending on the engine, testing may involve:

• Resistance

• Current draw

• Current waveform

• Injector activation

• Balance testing

• Manufacturer-specific injector testing

An oscilloscope can be particularly useful when the fault is intermittent or when the injector waveform needs to be compared with another cylinder.

There is no universal injector resistance or voltage value that applies to every vehicle.

7. Swap the injector when appropriate

If the vehicle's design and manufacturer's procedure permit it, the cylinder #5 injector can sometimes be exchanged with another cylinder for diagnostic purposes.

If the fault moves with the injector, the injector becomes a strong suspect.

If the fault remains on cylinder #5, attention should shift toward the wiring, connector or ECM control circuit.

On some modern diesel systems, injector coding or calibration is required after replacement.

8. Check fuel pressure separately

If the injector circuit tests correctly, investigate fuel pressure and delivery.

Depending on the engine, this may involve checking the low-pressure supply, fuel filter, high-pressure pump and rail-pressure control system.

Normal fuel pressure does not rule out an electrical injector fault, and an electrical injector fault does not automatically indicate a fuel-pressure problem.

9. Check cylinder performance

If the injector circuit and injector itself appear healthy but cylinder #5 is still not operating correctly, investigate the mechanical condition of the cylinder.

Possible tests include:

• Compression test

• Leak-down test

• Valve inspection

• Valvetrain inspection

• Camshaft timing check

• VVT operation check

Why a Wiring Problem Can Be Misdiagnosed as a Bad Injector

This is particularly important with P0273.

Suppose the cylinder #5 injector has a low electrical condition. Replacing the injector may temporarily appear to solve the problem if the connector is disturbed during the repair, but the original wiring fault can remain.

If the fault returns, the injector may incorrectly be blamed again.

A proper diagnosis should therefore test the complete circuit, including the injector, connector, wiring, power supply and ECM control side.

P0273 vs P0274

These codes concern the same cylinder but describe opposite electrical conditions.

P0273 – Cylinder 5 Injector Circuit Low

The ECM detects an abnormally low electrical condition in the cylinder #5 injector circuit.

P0274 – Cylinder 5 Injector Circuit High

The ECM detects an abnormally high electrical condition in the cylinder #5 injector circuit.

Neither code automatically proves that the injector itself is defective.

P0273 vs P0275

These codes are also closely related but describe different types of faults.

P0273 – Cylinder 5 Injector Circuit Low

This is primarily an electrical injector circuit fault.

P0275 – Cylinder 5 Contribution / Balance Fault

This indicates that cylinder #5 is not contributing to engine operation as expected.

A P0273 injector circuit problem can cause poor combustion and subsequently lead to a contribution/balance problem, so both codes can appear together.

P0273 vs P0276

The difference is the cylinder number:

P0273 – Cylinder 5 Injector Circuit Low

P0276 – Cylinder 6 Injector Circuit Low

Both indicate a low electrical condition, but P0273 identifies cylinder #5 while P0276 identifies cylinder #6.

If both codes appear at the same time, it is worth checking whether the two injector circuits share a common power supply, wiring section or electrical ground.

Is P0273 Serious?

P0273 should be diagnosed promptly, particularly if the engine is running roughly.

If the Check Engine Light is steady and the engine operates normally, a short drive to a repair facility may be possible.

However, continued driving should be avoided if there is:

• Severe engine shaking

• Major power loss

• Flashing Check Engine Light

• Heavy misfire

• Stalling

• Strong fuel smell

• Excessive smoke

• Abnormal engine noise

A severe gasoline-engine misfire can send unburned fuel into the exhaust system and overheat the catalytic converter.

On diesel engines, serious injector problems can increase smoke, emissions and engine stress.

The Correct Way to Repair P0273

P0273 should be treated as an injector circuit electrical fault, rather than an automatic injector replacement code.

The best diagnostic sequence is to inspect the cylinder #5 injector and connector, examine the wiring, verify the injector power supply, check the control circuit and test the injector itself.

If those tests are satisfactory, fuel pressure and the mechanical condition of cylinder #5 should be investigated.

The ECM/PCM should generally be considered last.

The goal is not simply to make the P0273 code disappear. The goal is to determine why the ECM is seeing a low electrical condition in the cylinder #5 injector circuit and repair the actual cause.