SYMPTOM-FAILED-EMISSIONS Code — Failed emissions test — common codes and fixes (Causes & How to Fix)

Introduction to Failed Emissions Tests

A failed emissions test can be a frustrating experience for any vehicle owner. The SYMPTOM-FAILED-EMISSIONS code is a common issue that can be caused by a variety of factors, including a loose or damaged fuel cap, EVAP system leaks, oxygen sensor drift, catalytic converter deterioration, or faulty PCM or wiring. In this article, we will provide a step-by-step guide on how to diagnose and repair the SYMPTOM-FAILED-EMISSIONS code, including the most common causes, symptoms, and fixes.

Understanding the SYMPTOM-FAILED-EMISSIONS Code

The SYMPTOM-FAILED-EMISSIONS code is a catch-all code that indicates that the vehicle’s emissions system is not functioning properly. This code can be triggered by a variety of factors, including:

• A loose or damaged fuel cap, which can cause fuel vapors to escape and trigger the code.
• EVAP system leaks, which can cause fuel vapors to bypass the charcoal canister and trigger the code.
• Oxygen sensor drift, which can cause the sensor to provide inaccurate readings and trigger the code.
• Catalytic converter deterioration, which can cause the converter to fail to reduce CO, HC, and NOx emissions, triggering the code.
• Faulty PCM or wiring, which can cause false data to be sent to the PCM, triggering the code.

Symptoms of the SYMPTOM-FAILED-EMISSIONS Code

The symptoms of the SYMPTOM-FAILED-EMISSIONS code can vary depending on the underlying cause of the problem. Some common symptoms include:

• A check-engine light on the dashboard, which can be steady or flashing.
• A rough idle or occasional stalling after a cold start, which can be caused by an O₂ sensor that is stuck rich or lean.
• Decreased fuel economy, which can be caused by the PCM running a richer mixture to compensate for sensor errors.
• A sulfuric or “rotten egg” smell from the exhaust, which can indicate a failing catalytic converter.
• A visible fuel smell near the fuel tank or under the car, which can indicate an EVAP leak.

Diagnosing the SYMPTOM-FAILED-EMISSIONS Code

To diagnose the SYMPTOM-FAILED-EMISSIONS code, follow these steps:

1. Check the gas cap and obvious visual issues: Make sure the fuel cap is tightened to the click and look for cracked hoses, loose vacuum lines, or disconnected EVAP components.
2. Read live data and freeze-frame info: Connect an OBD-II scanner and pull the pending and stored codes. Note the fuel trim, O₂ sensor voltages, and EVAP pressure values at the time of the fault.
3. Test the primary oxygen sensor (Bank 1 Sensor 1): Using a digital multimeter, measure sensor voltage while the engine idles. A healthy sensor should swing between ~0.1 V (lean) and ~0.9 V (rich) every few seconds.
4. Inspect and test the EVAP purge valve: Remove the valve, apply 12 V to the coil, and listen for a click. Then measure voltage at the valve’s control wire while the PCM commands a purge; you should see ~5 V.
5. Check catalytic converter efficiency: Compare upstream (Bank 1 Sensor 1) and downstream (Bank 1 Sensor 2) O₂ sensor voltages. The downstream sensor should stay relatively steady (0.4-0.6 V) if the converter is working.
6. Perform a smoke test for EVAP leaks: Connect a smoke machine to the EVAP intake and watch for smoke escaping from hoses, the charcoal canister, or the fuel tank vent valve.

Fixing the SYMPTOM-FAILED-EMISSIONS Code

Once you have diagnosed the problem, you can start fixing it. Here are some common fixes:

• Replace the gas cap: If the gas cap is loose or damaged, replace it with a new one.
• Repair or replace the EVAP system: If you find a leak in the EVAP system, repair or replace the affected component.
• Replace the oxygen sensor: If the oxygen sensor is faulty, replace it with a new one.
• Replace the catalytic converter: If the catalytic converter is faulty, replace it with a new one.
• Repair or replace the PCM or wiring: If the PCM or wiring is faulty, repair or replace it with a new one.

Cost Estimates

The cost of repairing the SYMPTOM-FAILED-EMISSIONS code can vary depending on the underlying cause of the problem. Here are some estimated costs:

• Gas cap replacement: $10-$50
• EVAP system repair or replacement: $100-$500
• Oxygen sensor replacement: $50-$200
• Catalytic converter replacement: $500-$1,500
• PCM or wiring repair or replacement: $500-$2,000

Make-Specific Fixes

Here are some make-specific fixes for the SYMPTOM-FAILED-EMISSIONS code:

Toyota

The Toyota model most affected by the SYMPTOM-FAILED-EMISSIONS code is the Toyota Corolla (2014-2019) with the 1.8L engine. The typical root cause of the problem is a faulty oxygen sensor, which can cause the code to be triggered. The cost of replacing the oxygen sensor can range from $100 to $300, depending on the labor costs and the type of sensor used.

Honda

The Honda model most affected by the SYMPTOM-FAILED-EMISSIONS code is the Honda Civic (2016-2020) with the 2.0L engine. The typical root cause of the problem is a leak in the EVAP system, which can cause the code to be triggered. The cost of repairing the EVAP system can range from $200 to $500, depending on the labor costs and the type of repair needed.

Ford

The Ford model most affected by the SYMPTOM-FAILED-EMISSIONS code is the Ford F-150 (2015-2018) with the 3.5L engine. The typical root cause of the problem is a faulty catalytic converter, which can cause the code to be triggered. The cost of replacing the catalytic converter can range from $500 to $1,500, depending on the labor costs and the type of converter used.

Chevrolet

The Chevrolet model most affected by the SYMPTOM-FAILED-EMISSIONS code is the Chevrolet Silverado (2014-2018) with the 5.3L engine. The typical root cause of the problem is a faulty PCM or wiring, which can cause the code to be triggered. The cost of repairing or replacing the PCM or wiring can range from $500 to $2,000, depending on the labor costs and the type of repair needed.

Common Misdiagnoses

One common misdiagnosis of the SYMPTOM-FAILED-EMISSIONS code is to replace the catalytic converter without checking the oxygen sensor or EVAP system. This can lead to unnecessary repairs and costs. Another common misdiagnosis is to replace the PCM or wiring without checking the oxygen sensor or EVAP system. This can also lead to unnecessary repairs and costs.

Conclusion

The SYMPTOM-FAILED-EMISSIONS code can be a frustrating experience for any vehicle owner. However, by following the steps outlined in this article, you can diagnose and repair the problem quickly and efficiently. Remember to always check the gas cap, oxygen sensor, and EVAP system before replacing the catalytic converter or PCM. With the right tools and knowledge, you can save time and money and get your vehicle back on the road in no time.

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