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Diagnostic code P0420


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4 replies to this topic

#1 AllanC

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Posted May 25, 2010 at 08:26 pm

Vehicle is a 2008 Dodge Avenger with 2.4L 4 cylinder engine, 4 speed automatic transmission. Odometer reading is 52500 miles. In the last 7 weeks I have had some persistent diagnostic codes appear which have been difficult to resolve. The following link details the first encounter and I present it as reference.

http://www.allpar.co...

The ongoing problem with code P0017, exhaust cam sensor, has been difficult to solve. I cleaned sensor terminals, spread pins in the sensor to force tighter contact fit in the receptacle. All of these did not fix the problem as the code would reappear. The longest interval before code appearance was about 10 days.

Finally on Thursday evening, May 20, I decided to exchange the exhaust cam sensor with the intake cam sensor and clear code P0017 from the engine controller memory. No diagnostic code appeared for the intake sensor so I reasoned that if I swapped the sensors and the diagnostic code appeared on the intake side that would mean the sensor was defective. If code P0017 still appeared on the exhaust side that would indicate the sensor was good and the problem lies with the wiring.

Vehicle has been driven about 600 miles since May 20. Code P0017 and P0016 (exhaust and intake cam sensor) have not appeared. I am not complaining but it definitely seems odd that switching 2 sensors prevents a diagnostic fault code from appearing.

Of interest is the fact that the emission label underneath the hood indicates California emissions though the car was placed in rental fleet service in Texas. California emissions requirements are more stringent that the rest of the USA so that may be a factor in this discussion. Now the new problem. In scanning for any codes I am now getting pending code P0420, catalyst efficiency. I received that in early April and a dealership service department applied the software controller upgrade outlined in TSB # 18-018-07A. That eliminated code P0420. Now it is reappearing as a pending code but the check engine lamp has NOT illuminated. I used a scan tool to view the real time behavior of the upstream and downstream oxygen sensors. At 750 engine rpm and the engine at 212 deg F operating temperature, the upstream sensor switches between voltages .08, .10, .20, … , .70, .80, .90. So it appears to be functioning properly as it is switching smoothly between rich and lean conditions in the exhaust gas. The downstream sensor voltage readings at 750 rpm are .68 , .70, .71 . Are these voltages proper for the downstream sensor or should they be closer to .45?

From my research on the internet the downstream sensor should stay close to its midpoint value of .45 which would indicate neither rich nor lean. I believe the pending code P0420 is being set by the controller software because the voltage readings between the upstream and downstream sensors are too close to each other. Has the catalytic converter failed prematurely or is it possible that the downstream oxygen sensor is defective? I would think that if the downstream oxygen sensor failed it would set its own unique code. Any thoughts about this???

Edited by AllanC, May 25, 2010 at 08:39 pm.


#2 richd

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Posted May 25, 2010 at 10:38 pm

Vehicle is a 2008 Dodge Avenger with 2.4L 4 cylinder engine, 4 speed automatic transmission. Odometer reading is 52500 miles. In the last 7 weeks I have had some persistent diagnostic codes appear which have been difficult to resolve. The following link details the first encounter and I present it as reference.

http://www.allpar.co...

The ongoing problem with code P0017, exhaust cam sensor, has been difficult to solve. I cleaned sensor terminals, spread pins in the sensor to force tighter contact fit in the receptacle. All of these did not fix the problem as the code would reappear. The longest interval before code appearance was about 10 days.

Finally on Thursday evening, May 20, I decided to exchange the exhaust cam sensor with the intake cam sensor and clear code P0017 from the engine controller memory. No diagnostic code appeared for the intake sensor so I reasoned that if I swapped the sensors and the diagnostic code appeared on the intake side that would mean the sensor was defective. If code P0017 still appeared on the exhaust side that would indicate the sensor was good and the problem lies with the wiring.

Vehicle has been driven about 600 miles since May 20. Code P0017 and P0016 (exhaust and intake cam sensor) have not appeared. I am not complaining but it definitely seems odd that switching 2 sensors prevents a diagnostic fault code from appearing.

Of interest is the fact that the emission label underneath the hood indicates California emissions though the car was placed in rental fleet service in Texas. California emissions requirements are more stringent that the rest of the USA so that may be a factor in this discussion. Now the new problem. In scanning for any codes I am now getting pending code P0420, catalyst efficiency. I received that in early April and a dealership service department applied the software controller upgrade outlined in TSB # 18-018-07A. That eliminated code P0420. Now it is reappearing as a pending code but the check engine lamp has NOT illuminated. I used a scan tool to view the real time behavior of the upstream and downstream oxygen sensors. At 750 engine rpm and the engine at 212 deg F operating temperature, the upstream sensor switches between voltages .08, .10, .20, … , .70, .80, .90. So it appears to be functioning properly as it is switching smoothly between rich and lean conditions in the exhaust gas. The downstream sensor voltage readings at 750 rpm are .68 , .70, .71 . Are these voltages proper for the downstream sensor or should they be closer to .45?

From my research on the internet the downstream sensor should stay close to its midpoint value of .45 which would indicate neither rich nor lean. I believe the pending code P0420 is being set by the controller software because the voltage readings between the upstream and downstream sensors are too close to each other. Has the catalytic converter failed prematurely or is it possible that the downstream oxygen sensor is defective? I would think that if the downstream oxygen sensor failed it would set its own unique code. Any thoughts about this???


From what Ive read,if the downstream readings mirror upstream,then the converter is not doing its job.Once the converter is hot,the downstream sensor reading should show steady reading.Your correct on .45 voltage

Edited by richd, May 25, 2010 at 10:42 pm.


#3 DeanC

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Posted June 5, 2010 at 04:19 am

P0420 is set by excessive voltage differentials between upstream and downstream. With the engine warmed up and the converter working properly, there should be very little switching. If yours is showing those fuctuations, then it's a good guess that your converter is failing.

Edited by DeanC, June 5, 2010 at 04:20 am.


#4 ImperialCrown

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Posted June 5, 2010 at 05:28 am

You always want the O2 voltage to be changing. If it stands still, there is a problem. The upsteam O2 voltage will switch at a rate about twice as fast as the downstream O2 when fully warmed.
When the 'before and after' cat O2 sensor voltage switching become similar and the O2 sensors pass their self-tests, then the PCM will set a P0420 fault as the cat has lost it's effectiveness. It takes a while to set this cat fault as the PCM wants to be 'extemely certain' that the cat is actually failing. It can be very expensive for a car manufacturer to replace a cat in violation of federal emission laws (8 yr/80,000mi) and can prompt a nasty investigation, recall, etc.

#5 AllanC

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Posted June 5, 2010 at 10:43 pm

No diagnostic trouble codes have appeared since May 25. No code P0420, catalyst efficiency has appeared. So I believe these problems with various diagnostic codes P0017, P000B, P0420 over the last 2 months have been caused by less than robust (and incorrect) software in the engine controller. Since the catalytic converter has an 8/80 warranty I have about 30000 more miles to monitor the catalyst and see if this code P0420 appears again. Unfortunately we owners have no control over tweaking the software used in electronic engine management.


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