P0420 Subaru Code - Catalyst System Efficiency Below Threshold
Quick Answer
The Engine Control Module (ECM) monitors the switching frequency ratio of heated oxygen sensors 1 (front O2 sensor) and heated oxygen sensors 2 (rear O2 sensor). Common causes include Faulty Three-way Catalyst Converter Bank 1, Exhaust Tube, Intake Air Leaks. Severity is Moderate - service should be scheduled soon. The vehicle may still be drivable for short trips if it runs normally, but avoid hard driving and repair it soon.
- What it means
- P0420 Subaru indicates Catalyst System Efficiency Below Threshold.
- Common causes
- Common causes include Faulty Three-way Catalyst Converter Bank 1, Exhaust Tube, Intake Air Leaks.
- Severity
- Moderate - service should be scheduled soon.
- Can I drive?
- The vehicle may still be drivable for short trips if it runs normally, but avoid hard driving and repair it soon.
Code P0420 Subaru Description
A three way catalyst converter (Manifold) with high oxygen storage capacity will indicate a low switching frequency of heated oxygen sensor 2. As oxygen storage capacity decreases, the heated oxygen sensor 2 switching frequency will increase.
When the frequency ratio of heated oxygen sensors 1 and 2 approaches a specified limit value, the three way catalyst malfunction is diagnosed.
What are the Possible Causes of the DTC P0420 Subaru?
- Faulty Three-way Catalyst Converter Bank 1
- Exhaust Tube
- Intake Air Leaks
- Faulty Oxygen (O2) Sensor
- Faulty Fuel injector(s)
- Leaking Fuel Injector (s)
- Faulty Spark plugs
- Improper Ignition Timing
- Faulty Engine Control Module (ECM)
- Dirty Air Filter
How to Fix the DTC P0420 Subaru?
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.
Code Tech Notes
What is the Cost to Diagnose the Code?
Labor: 1.0
To diagnose the P0420 Subaru 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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Frequently Asked Questions about P0420 Subaru Code
1. What are the common symptoms of a P0420 OBDII code in a Subaru?
- Common symptoms include poor fuel economy, loss of engine power, rough idle, and the illumination of the check engine light.
2. What are the typical causes of a P0420 OBDII code in a Subaru?
- The main causes are a failing catalytic converter, faulty oxygen sensors, exhaust leaks, engine misfires, or a problem with the fuel system.
3. How can I diagnose a P0420 code in my Subaru?
- You can start by checking the oxygen sensor readings, inspecting the catalytic converter for damage, and looking for any exhaust leaks.
4. Can a P0420 code be triggered by a faulty oxygen sensor?
- Yes, a failing oxygen sensor can provide inaccurate readings to the engine control unit, leading to a P0420 code being triggered.
5. What are some repair tips for addressing a P0420 code in a Subaru?
- Repair options may include replacing the catalytic converter, oxygen sensors, fixing any exhaust leaks, addressing engine misfires, and ensuring proper fuel system operation.
6. Is it safe to continue driving my Subaru with a P0420 code?
- It is generally safe to drive the vehicle for a short period with a P0420 code, but it is recommended to address the issue promptly to prevent further damage and ensure optimal performance.
7. Can a P0420 code be a false alarm in a Subaru?
- Yes, sometimes a P0420 code can be triggered by temporary issues like bad fuel quality or sensor malfunctions. It is advisable to clear the code and monitor for recurrence before taking further action.
8. How much does it typically cost to repair a P0420 code in a Subaru?
- The cost of repairing a P0420 code can vary depending on the root cause, but it can range from a few hundred dollars for minor fixes to over a thousand dollars for catalytic converter replacement.
9. What are the long-term effects of ignoring a P0420 code in a Subaru?
- Ignoring a P0420 code can lead to decreased fuel efficiency, potential damage to other engine components, and may cause the vehicle to fail emissions tests.
10. Can I reset the check engine light to temporarily clear a P0420 code in my Subaru?
- While you can reset the check engine light to clear the code temporarily, it is crucial to address the underlying issue causing the P0420 code to prevent further problems.
Discuss the causes and fixes for P0420 Subaru OBDII Code
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Hi all! I've had the P0420 code intermittently for about 5 months on my '05 Outback 2.5L XT with 96K miles. At first it was "naked", now it's accompanied w/ P0133, and the two are still intermittent. I had the front HO2S replaced nearly 5 years ago due to a P0131 code at the time. Since the P0420 code started I've been doing some research on it and stumbled into this site. Good info.! Today I'm having that same sensor replaced again and codes erased. Hopefully that will be the end of my problems. In my area a functioning cat. con. is not required (just needs to be installed) so if the cat. con, is indeed the problem I'll drive the car that way until I trade it, at least a couple more years. I have a scanner so I can check for other codes and erase the nagging P0420 when it sets. I wouldn't even do that except that with Subarus we lose the cruise control anytime the CEL is illuminated, and for me that's totally unacceptable! I'll report back at some point. Cheers!
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