• Tiny
  • cochise 1
  • 2000 Pontiac Bonneville
  • 6 CYL
  • 2WD
  • automatic
  • 150,000 miles

I have a 2000 bonneville ssei. It has 2 02 sensors. I get the code that says cat. Sys. Efficency level low bank 1. Is that the upstream 02 or the downstream 02

Do you
have the same problem?
Sunday, February 13th, 2011 AT 8:28 PM

1 Reply

  • Tiny
  • rasmataz
  • Member

A code P0420 may mean that one or more of the following has happened:
Leaded fuel was used where unleaded was called for
An oxygen sensor is not reading (functioning) properly
The engine coolant temperature sensor is not working properly
Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
Retarded spark timing
The oxygen sensors in front and behind the converter are reporting too similar of readings
Possible SolutionsSome suggested steps for troubleshooting a P0420 error code include:
Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
Inspect the downstream heated oxygen sensor (HO2), replace if necessary
Replace the catalytic converter

Was this
Sunday, February 13th, 2011 AT 10:09 PM

Please login or register to post a reply.

Similar Questions