Ok so i have recently replaced my spark plugs and coil packs on my 07 expedition. Ever since then i have had the CEL come on for a couples of weeks then it will turn off for a few days. Took it to auto zone and it brought up a p0420 code. Im hoping its the 02 sensor. Anybody have this problem before? I just think its weird that the CEL light will turn on and off. If it was the converters would the light just stay on?
p0420 problem
- Thread starter Jdm5630
- Start date
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mrford60
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I would try a o2 sensor first. make sure you replace the second one (the downstream one) on the RH side
B
bedrck46
That code may indicate that both need to be changed
Description: Indicates the bank 1 catalyst system efficiency is below the acceptable threshold.
Possible Causes: Use of leaded fuel
Damaged heated oxygen sensor (HO2S)
Out of range engine coolant temperature (ECT) sensor
High fuel pressure
Damaged exhaust manifold
Damaged catalytic converter
Oil contamination
Cylinder misfiring
Downstream HO2S wires incorrectly connected
Damaged exhaust system pipe
Damaged muffler/tailpipe assembly
Retarded spark timing
Leaking fuel injector
Diagnostic Aids: Compare HO2S upstream HO2S11 and downstream HO2S12 switch rate and amplitude. Under normal closed loop fuel conditions, high efficiency catalysts have oxygen storage which makes the switching frequency of the downstream HO2S very slow and reduces the amplitude of those switches as compared to the upstream HO2S. As catalyst efficiency deteriorates, its ability to store oxygen declines and the downstream HO2S signal begins to switch more rapidly with increased amplitude, approaching the switching rate and amplitude of the upstream HO2S. Once beyond an acceptable limit the DTC is set.
Description: Indicates the bank 1 catalyst system efficiency is below the acceptable threshold.
Possible Causes: Use of leaded fuel
Damaged heated oxygen sensor (HO2S)
Out of range engine coolant temperature (ECT) sensor
High fuel pressure
Damaged exhaust manifold
Damaged catalytic converter
Oil contamination
Cylinder misfiring
Downstream HO2S wires incorrectly connected
Damaged exhaust system pipe
Damaged muffler/tailpipe assembly
Retarded spark timing
Leaking fuel injector
Diagnostic Aids: Compare HO2S upstream HO2S11 and downstream HO2S12 switch rate and amplitude. Under normal closed loop fuel conditions, high efficiency catalysts have oxygen storage which makes the switching frequency of the downstream HO2S very slow and reduces the amplitude of those switches as compared to the upstream HO2S. As catalyst efficiency deteriorates, its ability to store oxygen declines and the downstream HO2S signal begins to switch more rapidly with increased amplitude, approaching the switching rate and amplitude of the upstream HO2S. Once beyond an acceptable limit the DTC is set.
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