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trouble code P0420 Olds Alero
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lemoncoke
New User
Oct 4, 2008, 1:43 PM
Post #1 of 3
(13080 views)
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trouble code P0420 Olds Alero
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2001 Olds Alero 4cylinder 2.4L 144800 miles it has been getting only about 19 mpg. It has had the catalic converter replaced and the light came on again about 1 week later. What should I check for to get the milage up and what else could be wrong with the car with this code. I have a scan tool and it read the P0420 code, and the freeze frame read Fuel sys 1 ---- OL Fuel sys 2 --- CL FAULT Calc Load 18.04 %, ECT 1888, and STFT B1 (%) --0.00. The scan tool said Catalyst System Efficency Below Threshold ( Bank1). Please help me get my mpg better it is not that good right know. Thanks Rick
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DanD
Veteran
/ Moderator
Oct 6, 2008, 4:35 AM
Post #2 of 3
(13061 views)
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Re: trouble code P0420 Olds Alero
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It’s a shame that you replaced the converter on a guess or just because you retrieved the code.
I’ve seen so many people run out and throw parts at a vehicle just because the code “said so” or that’s what they were led to believe by the parts store.
Why do the part stores offer FREE code readings; it’s not because they want to be your hero; they want you to do exactly that; run in and buy a sensor or whatever that a code relates to. This “service” they provide; works great for them with their no return policy on electronic and emission devices.
As you’ve learnt now a P0420 that has a description of low catalyst efficiency, isn’t a declaration of the death for the converter.
By the way it sounds; you’re using a code reader not a scan tool. A code reader is just that, it will display codes and freeze frame but that is far from a scan tool that will give you access to sensor data and allow you to perform or command the computer to run specific tests.
With any code that sets, you have to stand back and think of all the different things that the PCM (computer) looks for before the PCM will even run a test that may cause that particular code to set.
With a P0420; the PCM will monitor how long the engine has been running (minimum of 520 seconds); the barometric pressure (72kPa), the vehicle has been driven above 1200rpm and the battery is above 9 volts.
Then once the vehicle has come to a stop, the engine is idling no more the 150 rpm from the desired rpm, the transmission is in drive, throttle position is at zero percent, the engine temperature is between 156 – 257 degrees, air intake temperature is between
-4 –176 degrees. All of this has to happen in a specific order, time frame and must stay consistent for 30 seconds.
Now if anyone of the above inputs to the PCM is inaccurate and the PCM is still allowed too run the test on the converter, it may set a code.
Then there are other factors that can come into play; are the O2 sensors functioning properly and showing the PCM the correct feedback, has there been a programming change for the PCM, to correct false codes from being set, is the basic engine running properly and the list goes on and on.
I know and I’m sorry that this doesn’t answer your question of, “what else could be wrong” but how can we give you an answer, when there are so many variables?
No; this is not an impossible thing to diagnose but it is one that takes equipment and a good understanding of how the system was intended to function.
One last thing to think about; the cost of the converter would have likely paid for the diagnosis of the actual cause?
Dan.
Canadian "EH"
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lemoncoke
New User
Oct 6, 2008, 4:01 PM
Post #3 of 3
(13053 views)
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Re: trouble code P0420 Olds Alero
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Thanks for the information,The cat converter was replaced by the shop that I bought the car from and I didn't have to pay for it so that was good . But he also put in a 02 sensor the second time I brought it back to him at no charge, and as you can guess I won't be bringing it back to him this time. Thanks for the info.
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