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  #1  
Old 08-20-2013, 06:27 PM
ramesh1981 ramesh1981 is offline
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2005 Altima Sedan
 
Join Date: Aug 2013
Posts: 1
Default Check Engine Light - P0420

Dear Sir,

I have a Nissan Altima 2.5S 2005 with 135000 miles on it. I had a check engine light come on about one month ago & when I took my car to brakes plus, they diagnosed the code & said that throtlle body needs replacement. they charged me 500 dollars & replaced the throttle body with an after market one. They had difficulty with idle learn process & they took about 2 days to have my car relearn the computer. Exactly after one month, the check engine light came back again & now this time it is P0420. I replaced the down stream oxygen sensor & that did not fix the problem. What I notice is my Car idles above 1500 RPM when in Parking, especially when I drive in traffic & come home, when I put my car in Parking before getting out, it idles above 1500 RPM. When I'm driving the car in Drive gear it does not have any issues. Only when the car is in parking it appears like its idling at higher RPM like 1200-1700 RPM. Even this behaviour is also not consistent, some times it idles only at 800-900 RPM in parking. I'm not sure if the ECM program is bad or its bad catalytic converter or something else. Please help me.

Regards,
Ramesh
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  #2  
Old 08-20-2013, 07:03 PM
NissanAltima01 NissanAltima01 is offline
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2003 Altima 2.5S
 
Join Date: Aug 2012
Posts: 327
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When replacing an oxygen sensor, both should be replaced and not just one. Try replacing the upstream oxygen sensor and if the code remains then you need to replace that catalytic converter. Your vehicle should be idling around 650-700, not 1200-1700. That 1200-1700 idle should only be for a few minutes during a cold start. The Idle re-learning procedure can be done manually or by a scan tool. Here is the manual procedure below. If this doesn't work for you then i would take it back to that shop and have them fix the issue.

1. Perform "Accelerator Pedal Released Position Learning".
a. Make sure that accelerator pedal is fully released.
b. Turn ignition switch 'ON' and wait at least 2 seconds.
c. Turn ignition switch 'OFF' wait at least 10 seconds.
d. Turn ignition switch 'ON' and wait at least 2 seconds.
e. Turn ignition switch 'OFF' wait at least 10 seconds.
2. Perform "Throttle Valve Closed Position Learning" .
a. Make sure that accelerator pedal is fully released.
b. Turn ignition switch 'ON'.
c. Turn ignition switch 'OFF' wait at least 10 seconds.
Make sure that throttle valve moves during above 10 seconds by confirming the operating sound.
3. Start engine and warm it up to normal operating temperature.
4. Turn ignition switch 'OFF' and wait at least 10 seconds.
5. Confirm that accelerator pedal is fully released, turn ignition switch 'ON' and wait 3 seconds.
6. Repeat the following procedure quickly five times within 5 seconds.
a. Fully depress the accelerator pedal.
b. Fully release the accelerator pedal.
7. Wait 7 seconds, fully depress the accelerator pedal and keep it for approx. 20 seconds until the MIL stops blinking and turned ON.
8. Fully release the accelerator pedal within 3 seconds after the MIL goes off.
9. Start engine and let it idle.
10. Wait 20 seconds.
11. Rev up the engine two or three times and make sure that idle speed and ignition timing are within the specifications.
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