AutoCodes – Cadillac – P0303 Cadillac

P0303 Cadillac 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 Cadillac 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 32,150

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 Cadillac 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 Cadillac - Cylinder 3 Misfire Detected - AutoCodes.com — P0303 Cadillac Code - Cylinder 3 Misfire Detected

What does this mean?

What are the Possible Causes of the DTC P0303 Cadillac?

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 Cadillac?

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".

There is a Factory Service Bulletins for All 2000-2020 Cadillac Models:
2000-2020 Cadillac Factory Service Bulletin OBDII Code P0303
This Factory Service Bulletin explains how this condition may be caused by significant carbon build-up on the intake and/or exhaust valves due to fuel contamination or incomplete burning of the fuel.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0303 Cadillac 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 Cadillac Code

1. What are the common symptoms of a P0303 Cadillac OBDII code?

A: Common symptoms include engine misfires, rough idling, loss of power, and potentially an illuminated check engine light.

2. What are the typical causes of a P0303 Cadillac code?

A: The most common causes include faulty ignition coils, spark plugs, fuel injectors, vacuum leaks, or a problem with the engine's compression.

3. How can I diagnose the source of a cylinder 3 misfire in my Cadillac?

A: You can use a scan tool to identify the specific cylinder causing the misfire, visually inspect the spark plug and ignition coil for damage, check for vacuum leaks, and perform a compression test on the engine.

4. Can a dirty fuel injector cause a P0303 code in a Cadillac?

A: Yes, a dirty or clogged fuel injector can lead to a cylinder 3 misfire, triggering the P0303 OBDII code.

5. What are some repair tips for fixing a P0303 Cadillac code?

A: Repair tips include replacing faulty spark plugs, ignition coils, or fuel injectors, addressing any vacuum leaks, performing an engine compression test, and ensuring proper fuel quality.

6. Is it safe to continue driving with a P0303 OBDII code in my Cadillac?

A: It is not recommended to continue driving with a cylinder 3 misfire detected, as it can lead to further damage to the engine and potentially worsen fuel efficiency.

7. How much does it typically cost to repair a P0303 Cadillac code?

A: The cost of repair can vary depending on the exact cause of the misfire, but it may range from $100 to $500 or more, including parts and labor.

8. Can a P0303 code be triggered by a bad ignition coil in a Cadillac?

A: Yes, a faulty ignition coil, especially on cylinder 3, can cause misfires and trigger the P0303 OBDII code.

9. Are there any preventive measures to avoid a P0303 code in a Cadillac?

A: Regular maintenance, such as replacing spark plugs and ignition components at recommended intervals, using quality fuel, and addressing any engine performance issues promptly, can help prevent cylinder misfires.

10. How long does it take to repair a P0303 Cadillac code?

A: The repair time can vary depending on the cause of the misfire and the extent of the necessary repairs, but it may take anywhere from a few hours to a full day at a professional repair shop.