AutoCodes – Hummer – P0303 Hummer

P0303 Hummer Code - Cylinder 3 Misfire Detected

Quick Answer

A misfiring cylinder causes slight variations in the rotational speed of the crankshaft. Common causes include Faulty Spark Plug #3, Clogged or faulty Fuel Injector #3, Faulty Ignition Coil #3. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means: P0303 Hummer indicates Cylinder 3 Misfire Detected.
Common causes: Common causes include Faulty Spark Plug #3, Clogged or faulty Fuel Injector #3, Faulty Ignition Coil #3.
Severity: High - diagnose this code as soon as possible.
Can I drive?: Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

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Code Popularity 10,773

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Jul 21, 2022

Description
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code P0303 Hummer Description

A misfiring cylinder causes slight variations in the rotational speed of the crankshaft. The Engine Control Module (ECM) can detect these variations by closely monitoring the crankshaft position sensor signal. The signals of the camshaft position sensors are used to determine which cylinder is misfiring. If the ECM detects a misfire rate sufficient to cause emission levels to exceed mandated standards, the Diagnostic Trouble Code (DTC) will be set. Under certain driving conditions, a misfire rate can be high enough to cause the catalytic converter to overheat, damaging the converter. The Malfunction Indicator Lamp (MIL) flashes when the converter is overheating, damaging conditions are present, and the DTC is set. The DTC will be set when the ECM detects a crankshaft rotation speed variation indicating a single-cylinder misfire rate sufficient to cause emissions levels to exceed mandated standards.

OBDII Code P0303 Hummer - Cylinder 3 Misfire Detected - AutoCodes.com — P0303 Hummer Code - Cylinder 3 Misfire Detected

What does this mean?

What are the Possible Causes of the DTC P0303 Hummer?

Faulty Spark Plug #3
Clogged or faulty Fuel Injector #3
Faulty Ignition Coil #3
Fuel Injector #3 harness is open or shorted
Fuel Injector #3 circuit poor electrical connection
Ignition Coil #3 harness is open or shorted
Ignition Coil #3 circuit poor electrical connection
Insufficient cylinder 3 compression
Incorrect fuel pressure
Intake air leak

How to Fix the DTC P0303 Hummer?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What does this mean?

Code Tech Notes

The P0303 code means that cylinder 3 is misfiring or is randomly misfiring. Start by checking for intake leaks and if no leaks are found the next step is to replace the spark plugs on cylinder 3. If the problem persists more tests need to be done to diagnose the problem, see "Possible Causes".

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0303 Hummer code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

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About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about P0303 Hummer Code

1. What are the common symptoms of OBDII code P0303 (Cylinder 3 Misfire Detected) in a Hummer?

A misfire in cylinder 3 can cause symptoms such as rough idling, loss of power, engine vibration, and potentially increased fuel consumption.

2. What are the typical causes of a cylinder 3 misfire in a Hummer triggering code P0303?

Possible causes include faulty spark plugs, a malfunctioning ignition coil, clogged fuel injector, vacuum leak, low compression in the cylinder, or a problem with the engine's computer.

3. How can I diagnose the specific cause of a cylinder 3 misfire in my Hummer with code P0303?

Diagnostic steps may involve checking and testing the spark plugs, ignition coil, fuel injector, compression levels, vacuum lines, and the engine control module using specialized tools and equipment.

4. Can driving with OBDII code P0303 (Cylinder 3 Misfire Detected) in a Hummer cause further damage?

Continuing to drive with a cylinder misfire can potentially damage the catalytic converter, oxygen sensor, or other engine components over time. It is best to address the issue promptly.

5. Are there any quick repair tips for addressing OBDII code P0303 in a Hummer?

Quick fixes may include replacing the spark plugs, checking and cleaning the fuel injector, ensuring proper ignition coil function, and addressing any vacuum leaks in the system.

6. Should I reset the OBDII code P0303 (Cylinder 3 Misfire Detected) after addressing the issue in my Hummer?

After repairing the root cause of the misfire, it is recommended to clear the error code using an OBDII scanner to reset the Check Engine Light and monitor if the issue reoccurs.

7. Can bad fuel quality or fuel additives contribute to OBDII code P0303 in a Hummer?

Poor-quality fuel or certain fuel additives may lead to carbon buildup on spark plugs or fuel injectors, potentially causing a cylinder misfire and triggering code P0303.

8. How can I prevent OBDII code P0303 (Cylinder 3 Misfire Detected) from occurring in my Hummer in the future?

Regular maintenance, such as changing spark plugs at recommended intervals, using high-quality fuel, keeping the ignition system in good condition, and addressing engine issues promptly, can help prevent cylinder misfires.

9. Is it safe to drive my Hummer with a flashing Check Engine Light due to code P0303 (Cylinder 3 Misfire Detected)?

A flashing Check Engine Light indicates a severe misfire that can lead to catalytic converter damage. It is advisable to avoid driving the vehicle and seek professional assistance to prevent potential harm to the engine.

10. How much does it typically cost to repair OBDII code P0303 in a Hummer at a professional auto repair shop?

The cost of repairing a cylinder misfire causing code P0303 can vary based on the root cause, parts needed, and labor charges. It is recommended to obtain estimates from multiple reputable shops for an accurate cost assessment.