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Old 09-15-2008, 03:11 PM   #1 (permalink)
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2000 Elantra. Have check engine light on and fuel economy is down. Getting codes P0135 & P0131. Went ahead and replaced pre-cat oxy sensor, but it did not resolve issue. Any ideas? Thank you.
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Old 09-18-2008, 11:24 AM   #2 (permalink)
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Try changing the o2 sensor first.

hmaservice.com

You probably can get more info if you posted it in the Elantra forum. I had the same issue with my GF's car.
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Old 11-10-2012, 02:50 AM   #3 (permalink)
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By the way... The emissions control system runs in a "Closed Loop" configuration. This means that all the sensors (Throttle Position, Mass Air Intake, Engine Temps, Pre Cat and Post Cat Oxygen Sensors, and Timing Sensors) provide input to dynamically tune the vehicle. This gives the "optimal" gas mileage (s seriously debated issue in Engineering circles).
..
When the check engine light is on - the system shift into fail-safe (because the alternative is to disable the engine). This means the system shifts into the "Open Loop" configuration and rely's on EPA approved engine maps and performance tables to keep the engine running until the issue/problem can be fixed. In a nut shell, the check engine light is on and the car will continue to run to allow you to take it in to get serviced (as opposed to towing it in). In "Open Loop" the car will get the "worst" gas mileage.
...
Here is a hint that no one at the dealer will tell you too.... When a check engine light is flashing, instead of staying on steady - it means that there is an issue with the exhaust gasses that will put your catalytic converter at risk, and also is most likely to cause the catalytic converter to over heat. This can be as simple as too much MMBT (a common additive in low grade gas). Or a fuel air mixture that is too rich and causing fuel vapors to reach the Cat. It can be a leaky injector, foreign chemicals in the gas, or just fouled plugs or bad wires that aren't bad enough to register a "code" but bad enough to degrade engine efficiency.
..
Our Accent did this, the dealer said that it probably wasn't a serious enough condition to result in a "Check Engine Light" condition. Suggested we put it in for service (Only a $300) Diagnostics charge + Any parts and labor.
..
Mulling around an "Automotive Engineering Forum" I learned that flashing check engine lights are not full blown errors - but are meant as warnings that you are endangering your Catalytic Converter )In the case of the Accent it's only a $795 part - ouch). This code condition was added as recent as 2001, but for some reason isn't an actual published code condition (Go figure).
...
In our case it resulted in replacing the Coil Blocks, The Wires and plugs, The EGR Valve, All the Injectors, The $795 Catalytic Converter, and both Oxygen Sensors - the light is still blinking. But the worst is that the second "specialist shop" that the Hyundai dealer sent the car to just replaced the coil blocks (again) and the plugs and wire - now they are saying maybe an engine over haul.....
..
So don't be lulled into thinking just because the dealer blows it off that it is trivial - it isn't...
...
Dave Phoenix AZ
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Old 01-10-2013, 07:20 AM   #4 (permalink)
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Quote:
Originally Posted by dataman19 View Post
By the way... The emissions control system runs in a "Closed Loop" configuration. This means that all the sensors (Throttle Position, Mass Air Intake, Engine Temps, Pre Cat and Post Cat Oxygen Sensors, and Timing Sensors) provide input to dynamically tune the vehicle. This gives the "optimal" gas mileage (s seriously debated issue in Engineering circles).
..
When the check engine light is on - the system shift into fail-safe (because the alternative is to disable the engine). This means the system shifts into the "Open Loop" configuration and rely's on EPA approved engine maps and performance tables to keep the engine running until the issue/problem can be fixed. In a nut shell, the check engine light is on and the car will continue to run to allow you to take it in to get serviced (as opposed to towing it in). In "Open Loop" the car will get the "worst" gas mileage.
...
Here is a hint that no one at the dealer will tell you too.... When a check engine light is flashing, instead of staying on steady - it means that there is an issue with the exhaust gasses that will put your catalytic converter at risk, and also is most likely to cause the catalytic converter to over heat. This can be as simple as too much MMBT (a common additive in low grade gas). Or a fuel air mixture that is too rich and causing fuel vapors to reach the Cat. It can be a leaky injector, foreign chemicals in the gas, or just fouled plugs or bad wires that aren't bad enough to register a "code" but bad enough to degrade engine efficiency.
..
Our Accent did this, the dealer said that it probably wasn't a serious enough condition to result in a "Check Engine Light" condition. Suggested we put it in for service (Only a $300) Diagnostics charge + Any parts and labor.
..
Mulling around an "Automotive Engineering Forum" I learned that flashing check engine lights are not full blown errors - but are meant as warnings that you are endangering your Catalytic Converter )In the case of the Accent it's only a $795 part - ouch). This code condition was added as recent as 2001, but for some reason isn't an actual published code condition (Go figure).
...
In our case it resulted in replacing the Coil Blocks, The Wires and plugs, The EGR Valve, All the Injectors, The $795 Catalytic Converter, and both Oxygen Sensors - the light is still blinking. But the worst is that the second "specialist shop" that the Hyundai dealer sent the car to just replaced the coil blocks (again) and the plugs and wire - now they are saying maybe an engine over haul.....
..
So don't be lulled into thinking just because the dealer blows it off that it is trivial - it isn't...
...
Dave Phoenix AZ
Nicely stated!
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