AutoCodes – Scion – P0303 Scion

P0303 Scion Code - Cylinder 3 Misfire Detected

Quick Answer

When the engine misfires, high concentrations of Hydrocarbons (HC) enter the exhaust gas. Common causes include Intake air leak, Faulty spark plug #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 Scion indicates Cylinder 3 Misfire Detected.
Common causes: Common causes include Intake air leak, Faulty spark plug #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 23,879

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 Aug 25, 2022

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

When the engine misfires, high concentrations of Hydrocarbons (HC) enter the exhaust gas. Extremely high hydrocarbon concentration levels can cause an increase in exhaust emission levels. Extremely high concentrations of hydrocarbons can also cause increases in the three-way catalytic converter temperature, which may cause damage to the three-way catalytic converter. To prevent this increase in emissions and to limit the possibility of thermal damage, the Engine Control Module (ECM) monitors the misfire count. When the temperature of the three-way catalytic converter reaches the point of thermal degradation, the ECM blinks the MIL. To monitor misfires, the ECM uses both the camshaft position sensor and the crankshaft position sensor. The camshaft position sensor is used to identify any misfiring cylinders and the crankshaft position sensor is used to measure variations in the crankshaft rotation speed. Misfires are counted when the crankshaft rotation speed variations exceed predetermined thresholds. If the misfire count exceeds the threshold levels and could cause emission control system performance deterioration, the ECM illuminates the MIL and stores a Diagnostic Trouble Code (DTC).

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

What does this mean?

What are the Possible Causes of the DTC P0303 Scion?

Intake air leak
Faulty spark plug #3
Faulty ignition coil #3
Clogged or faulty fuel injector #3
Fuel injectors #3 harness is open or shorted
Fuel Injectors #3 circuit poor electrical connection
Ignition coils #3 harness is open or shorted
Ignition coils #3 circuit poor electrical connection
Incorrect Fuel pressure
Faulty Mass Air Flow (MAF) Sensor
Faulty Engine Control Module (ECM)
Faulty Engine Coolant Temperature (ECT) Sensor

How to Fix the DTC P0303 Scion?

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" for the most common problems.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0303 Scion 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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Information for Specific Scion Models

P0303 2005 Scion xB — Cylinder 3 Misfire Detected
P0303 2006 Scion xB — Cylinder 3 Misfire Detected
P0303 2007 Scion xB — Cylinder 3 Misfire Detected

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 Scion Code

No Frequently Asked Questions about P0303 Scion Code found.

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Cory Rodriguez
Date: February 2, 2018 at 2:27 am

I had a new heater core put in 2006 scion tc. heater works but now my engine light is on ant reads 303 misfire .....coincidence or can this be caused by shitty mechanic work. a week after replacing HC mt car over heated and heater quit working . they said it was bad radiator cap ? wouldn't they check something like that when dealing with cooling system? frustrated!!!

Reply to Comment
OBDIITech
Date: February 4, 2018 at 1:14 am

Coincidence, unless the mechanic remove some engine part to replace the heater core, which is unusual, and forgot connected back, then replacing the heater core has nothing to do with the cylinder misfire.

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