04 NB Mazdaspeed issues
01-15-2022, 09:14 AM
#1
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Join Date: Jan 2022
Posts: 2
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04 NB Mazdaspeed issues
Hello everyone,
Been having check engine light on with code P0420 for couple of months and just replaced a new 2nd o2 sensor at a shop. The light came back on, I took it back to the shop and I was told the reason is no reading on that new sensor, need to tear the interior down to check the wire. I bought this vehicle a year ago, no issues with driving dynamic/power. 2004 with 20k mileage.
Bought sensor from rockauto.com, the part itself is fine after test. The vehicle is at the shop now, I will ask and update if there is new code after replacing o2 sensor.
Wondering if anyone experienced similar issue, and whats my best solution here.
Thank you!
Been having check engine light on with code P0420 for couple of months and just replaced a new 2nd o2 sensor at a shop. The light came back on, I took it back to the shop and I was told the reason is no reading on that new sensor, need to tear the interior down to check the wire. I bought this vehicle a year ago, no issues with driving dynamic/power. 2004 with 20k mileage.
Bought sensor from rockauto.com, the part itself is fine after test. The vehicle is at the shop now, I will ask and update if there is new code after replacing o2 sensor.
Wondering if anyone experienced similar issue, and whats my best solution here.
Thank you!
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01-15-2022, 10:21 AM
#2
Senior Member
Join Date: Mar 2017
Location: Granbury Texas
Posts: 668
Total Cats: 190
P0420 is a code for cat efficiency. The parameters require both upstream and downstream O2 sensors to be functional and the ECU looks at the difference between the two sensors to determine is the cat is working.
Normally if you have this code and NO other O2 sensor codes then you have killed your cat.
I've not seen this happen to a Japanese car below 100K, most make 200K plus before the cat dies (stock cars no mods)
If you have broken wiring you should ALSO have codes for the O2 sensor.
It is possible for bad o2 sensors to kick a 420 but I've never seen that without other O2 sensor codes.
If I have a 420 and other o2 sensor codes I will normally replace both of the O2 sensor (or 4 in something that has 2 cats).
I only buy stock, NTK, Denso, or Bosch O2 sensors.
Sometimes just replacing one will end up throwing a 420 and the o2 sensors age and an old and a new can confuse the ECU.
A no name cheap *** O2 sensor might be trash right out of the box. You should still have 02 codes with the 420.
If the wiring was broken, you should have o2 sensor codes.
I never seen a stock vehicle have these issues with only 20K but you are a little bit strange (17 years and only 20 k) so I'd believe sensors before cat...
A poorly modded/tuned car might kill a cat in 20k miles. MSMs were not tuned well by Mazda but I would not expect dead cat before 100K anyway.
A good shop should be able to look at the patterns the two sensors are putting out and accurately determine what is going on
Normally if you have this code and NO other O2 sensor codes then you have killed your cat.
I've not seen this happen to a Japanese car below 100K, most make 200K plus before the cat dies (stock cars no mods)
If you have broken wiring you should ALSO have codes for the O2 sensor.
It is possible for bad o2 sensors to kick a 420 but I've never seen that without other O2 sensor codes.
If I have a 420 and other o2 sensor codes I will normally replace both of the O2 sensor (or 4 in something that has 2 cats).
I only buy stock, NTK, Denso, or Bosch O2 sensors.
Sometimes just replacing one will end up throwing a 420 and the o2 sensors age and an old and a new can confuse the ECU.
A no name cheap *** O2 sensor might be trash right out of the box. You should still have 02 codes with the 420.
If the wiring was broken, you should have o2 sensor codes.
I never seen a stock vehicle have these issues with only 20K but you are a little bit strange (17 years and only 20 k) so I'd believe sensors before cat...
A poorly modded/tuned car might kill a cat in 20k miles. MSMs were not tuned well by Mazda but I would not expect dead cat before 100K anyway.
A good shop should be able to look at the patterns the two sensors are putting out and accurately determine what is going on
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01-15-2022, 10:52 AM
#3
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Thread Starter
Join Date: Jan 2022
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P0420 is a code for cat efficiency. The parameters require both upstream and downstream O2 sensors to be functional and the ECU looks at the difference between the two sensors to determine is the cat is working.
Normally if you have this code and NO other O2 sensor codes then you have killed your cat.
I've not seen this happen to a Japanese car below 100K, most make 200K plus before the cat dies (stock cars no mods)
If you have broken wiring you should ALSO have codes for the O2 sensor.
It is possible for bad o2 sensors to kick a 420 but I've never seen that without other O2 sensor codes.
If I have a 420 and other o2 sensor codes I will normally replace both of the O2 sensor (or 4 in something that has 2 cats).
I only buy stock, NTK, Denso, or Bosch O2 sensors.
Sometimes just replacing one will end up throwing a 420 and the o2 sensors age and an old and a new can confuse the ECU.
A no name cheap *** O2 sensor might be trash right out of the box. You should still have 02 codes with the 420.
If the wiring was broken, you should have o2 sensor codes.
I never seen a stock vehicle have these issues with only 20K but you are a little bit strange (17 years and only 20 k) so I'd believe sensors before cat...
A poorly modded/tuned car might kill a cat in 20k miles. MSMs were not tuned well by Mazda but I would not expect dead cat before 100K anyway.
A good shop should be able to look at the patterns the two sensors are putting out and accurately determine what is going on
Normally if you have this code and NO other O2 sensor codes then you have killed your cat.
I've not seen this happen to a Japanese car below 100K, most make 200K plus before the cat dies (stock cars no mods)
If you have broken wiring you should ALSO have codes for the O2 sensor.
It is possible for bad o2 sensors to kick a 420 but I've never seen that without other O2 sensor codes.
If I have a 420 and other o2 sensor codes I will normally replace both of the O2 sensor (or 4 in something that has 2 cats).
I only buy stock, NTK, Denso, or Bosch O2 sensors.
Sometimes just replacing one will end up throwing a 420 and the o2 sensors age and an old and a new can confuse the ECU.
A no name cheap *** O2 sensor might be trash right out of the box. You should still have 02 codes with the 420.
If the wiring was broken, you should have o2 sensor codes.
I never seen a stock vehicle have these issues with only 20K but you are a little bit strange (17 years and only 20 k) so I'd believe sensors before cat...
A poorly modded/tuned car might kill a cat in 20k miles. MSMs were not tuned well by Mazda but I would not expect dead cat before 100K anyway.
A good shop should be able to look at the patterns the two sensors are putting out and accurately determine what is going on
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01-15-2022, 11:40 AM
#5
Senior Member
Join Date: Mar 2017
Location: Granbury Texas
Posts: 668
Total Cats: 190
I have a nice 100K MSM but...
A 20K MSM should be "New".
Only problem for me with a 20K is I would probably not mod it as 10 years from now it will be worth more stock (maybe 50% more).
If it's nice it's worth 25K+ now!
That's a killer find...
A 20K MSM should be "New".
Only problem for me with a 20K is I would probably not mod it as 10 years from now it will be worth more stock (maybe 50% more).
If it's nice it's worth 25K+ now!
That's a killer find...
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01-16-2022, 09:56 AM
#6
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Join Date: Jun 2010
Location: Minneapolis, MN
Posts: 247
Total Cats: 38
I believe the rear O2 sensor wiring is under the driver seat. Four bolts to pull the seat (don't forget to unclip the seatbelt warning wires), pull up on the door piece to unclip so you can pull the carpet back, and see what you find. Tracing the wires back to the ECU under the dash shouldn't be difficult. The kick panel has one or two plastic retaining pins, pull up on the center part with your fingernail or small screwdriver and pop them out, then pull to release the metal clips. You might also have to pull the door seal away from the body to remove the kick panel.
This is mostly from memory reading here over the last decade or two. The, last time I messed with the rear O2 sensor it was to install a spacer to see if I could avoid having to replace a dead catalytic convertor on a 1999 Miata. Previous owner misled me and lied, having disconnected the battery to hide check engine error codes. It illuminated on my 45 minute drive home and led me to uncover other issues the ECU reset hid on my test drive. Idiot ignored the weak coil pack which killed the catalyst. If your car had bad wires/plugs, or a coil which would be rare at such low mileage and is usually more an issues on 1999/2000 cars, the cat might need to be replaced. Trace those wires and figure out why they are saying there is no rear O2 signal.
This is mostly from memory reading here over the last decade or two. The, last time I messed with the rear O2 sensor it was to install a spacer to see if I could avoid having to replace a dead catalytic convertor on a 1999 Miata. Previous owner misled me and lied, having disconnected the battery to hide check engine error codes. It illuminated on my 45 minute drive home and led me to uncover other issues the ECU reset hid on my test drive. Idiot ignored the weak coil pack which killed the catalyst. If your car had bad wires/plugs, or a coil which would be rare at such low mileage and is usually more an issues on 1999/2000 cars, the cat might need to be replaced. Trace those wires and figure out why they are saying there is no rear O2 signal.
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