1999 Toyota Corolla Check Engine Light P0420 - Catalyst bel

Tiny
ZONRYZA
  • MEMBER
  • 1999 TOYOTA COROLLA
  • 4 CYL
  • 2WD
  • MANUAL
  • 183,000 MILES
My check engine light came on the 1st time, reason was the 02 sensors were burned out. Replaced them ($400 incl. Labor). Then, 2 weeks later, check engine light came on. The reason this time: reading was a P0420, catalyst below threshold, bank 1. Mechanic suggested that I change oxygen sensors, perhaps the cables, too. I decided to wait. 2 days later, the check engine light turned off. Is there any rhyme or reason to this?
Monday, November 10th, 2008 AT 9:56 AM

3 Replies

Tiny
MMPRINCE4000
  • MECHANIC
  • 8,548 POSTS
The original bad O2 sensors could have cause the engine to run rich, causing the convertor to get abnormally hot. Changing the sensors cured the problem but it may have taken some time to get the convertor back to a normal range.

I would not be concerned at this point. Take it to any autoparts store and have the PCM scanned, if this code appears as a history code, I would erase it.
If it appears as a pending code, then I would have a convertor backpressure test performed to see if there is any restriction in the convertor.
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Tuesday, November 11th, 2008 AT 8:24 AM
Tiny
ZONRYZA
  • MEMBER
  • 2 POSTS
I must update y story about my 1999 Toyota Corrollla from a few months ago when it had the 02 sensor misfire problem. That problem was corrected. However, 3 weeks ago, I noticed my car was "preparing" me for another problem. I felt the car periodically "skip", or "miss", or "lurch" after changing gears, and thought my transmission or clutch was defective. However, finally it started "skipping" on me again BIG TIME and the Check Engine Light was flashing like crazy. I took it to the mechanic, and he examined and determined that the COIL PACK was defective. How did he determine this? He put the car up to the little computer to read the Check Engine code, and again it said 02 Sensor misfire. So, he changed the plug, drove the car, and it started throwing sparks. So. He changed the coil pack, and it's all good now!
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Tuesday, April 14th, 2009 AT 8:49 AM
Tiny
MMPRINCE4000
  • MECHANIC
  • 8,548 POSTS
Glad to hear it!
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Wednesday, April 15th, 2009 AT 6:29 AM

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