Question about 2001 Volkswagen Jetta TDI

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Had downstream oxygen sensor replaced in 2001 jetta v6. now it's loud when idling and runs rough.

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  • volvo90 Mar 19, 2011

    when i cliked on those links all i see are advertisements and some comments that are too light to read. can you let me know specifically what worked for you. thanks. i'm trying to get my son's car fixed before he drives it back to california after being in afghanistan for a year.

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Sounds like it was installed incorrectly. If that's the case you may have an exhaust leak and the sensor will not read the correct air/fuel ratio causing the engine to run poorly.

Posted on Mar 29, 2011

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Posted on Jan 02, 2017

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Can a bad downstream oxygen sensor cause a rough idle on a 2003 chevy venture


no, the downstream sensors do not feedback into the control of the engine--they only detect the effectiveness of the catalytic converters. If the sensor is detecting excess fuel, the problem could be with your fuel pressure regulator, and that would also explain the rough idle. Do you have a trouble code you can pass to me?

Dec 12, 2010 | 2003 Chevrolet Venture Passanger

2 Answers

Need a pic or diagram of location of Bank 2 sensor location on a 2004 Acura TL 3.2


Oxygen Sensor-I don't have a location of the Bank 2 sensor, so you'll have to guess on it by determining how many sensors you have by inspecting the exhaust system from the exhaust manifold down to the catalytic converter and past the catalytic converter which is downstream. Anything before the catalytic converter is upstream.
Do you have a code that describes which O2 sensor is not responding correctly?

Test/Replace
  • The sensor is threaded into the exhaust manifold.
  • It can be difficult to remove unless a special anti-seize compound is coated onto its threads.
  • Torque the sensor to 30 foot-pounds using a special socket.
  • A sensor that is too loose or a cracked exhaust manifold can result in a lean signal to the computer.
  • Check the vents in the thimble of a replacement O2 sensor.
  • There should be the same number of holes and they should face clockwise or counterclockwise like the ones on the original sensor.
  • Installing the wrong sensor can result in slower cross counts.

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Operation
Although the oxygen sensor is termed a sensor, in actuality it is a galvanic battery. The oxygen sensor compares the potential difference between the ambient oxygen content around the exhaust and the oxygen content present in the exhaust stream. When the exhaust sample is lean, there is more oxygen in the exhaust as compared to the atmosphere. When the exhaust sample is rich, there is less oxygen content in the exhaust as compared to the atmosphere. The greater the difference between ambient oxygen and exhaust oxygen content, the greater the voltage produced.
For the oxygen sensor(s) to operate properly, it has to reach an operating temperature of approximately 600°F before a consistent voltage potential can be generated.
The Engine Management System (EMS) determines the state of readiness of the oxygen sensors by supplying a bias voltage of approximately 400 - 500mVDC to the oxygen sensor. As the sensor begins to warm up, the voltage produced increases due to rich exhaust mixtures commanded by the EMS. When the EMS senses a return voltage greater than the bias voltage, the computer will command the fuel mixture lean. When the output voltage from the sensor drops below bias voltage levels, the computer will command a rich mixture again. When the EMS determines that the O2 sensor has responded properly and within a predetermined amount of time, it will begin using the sensor as an input to adjust fuel trim.
Many Oxygen sensors used in OBD 2 engine management systems incorporate heaters. These heaters raise the sensors up to operating temperature quickly. The sooner the oxygen sensor gets to operating temperature, the sooner the EMS can maintain closer control over emissions, economy and performance. The oxygen sensor provides the computer with necessary information to maintain favorable operating conditions for the catalytic converter. The role of the catalytic converter is to store oxygen for the reduction of HC, CO and NOx emissions. The oxygen sensor input is used by the EMS to protect the catalytic converter by cycling the air/fuel mixture rich and lean. This provides adequate oxygen for storage while maintaining cool enough operating temperatures to prevent catalyst damage.
In addition to controlling the converters operating conditions for emissions control, the computer uses the oxygen sensors to tailor fuel trim providing a balance between fuel economy and performance.
Abnormal sensor activity has a profound effect on pulse-width and fuel trim strategies. Sensor values that indicate lean conditions will cause the computer to command changes in short term fuel strategies. Conditions such as secondary misfires create excessive HC levels. This also produces high oxygen levels in the exhaust. The oxygen sensor will sense only the increased oxygen content and input to the computer will be below bias voltage levels. The computer will respond by commanding additional fuel.
OBD 2 vehicles use oxygen sensors downstream of the converter(s) to monitor the efficiency of the catalyst. When the catalyst performs properly, available oxygen is used resulting in low levels oxygen in the exhaust sample. While downstream oxygen sensors are constructed the same as upstream oxygen sensors, the values that they generate are different. With relatively richer mixtures present around the downstream oxygen sensor, voltage inputs to the computer will be above the 450mV bias voltage. If the catalyst is operating effectively, the downstream oxygen sensor will cycle when the catalyst is flooded with oxygen. Typical values from the downstream oxygen sensor(s) are between 550- 900mV at idle.
While the downstream oxygen sensor is used to monitor catalyst efficiency, the upstream sensor has a pronounced effect on performance. Lean oxygen sensor values will result in an increase in pulse-width, excessive emissions, surging, hesitation, and potentially catalyst damage. Additional fuel can cause the catalyst temperatures to rise due to an afterburner effect in the converter. The oxygen sensor is the only post combustion input to the EMS. Other malfunctioning systems affect its operation.
Improper rich indications will cause lean operating conditions that may result in loss of power, hesitation, surging, poor idle quality and possibly converter damage. Sensors that do not switch properly, or are lazy do not provide accurate information to allow the computer to properly maintain the air/fuel mixture. Faulty heaters do not allow the sensors to reach operating temperature fast enough and the vehicle may remain in open loop for longer periods of time. Malfunctioning heaters also allow the sensors to cool down during periods of extended idle.
A faulty oxygen sensor due to loose connections, bad grounds, high resistance in the circuit, or opens in the circuit can cause the following symptoms.
Related Symptoms
  • Surging at idle
  • Unstable idle
  • Running rough off idle
  • Hesitation
  • Stumble
  • Chuggle
  • Poor fuel economy
  • Spark knock
  • Stalling on acceleration
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Oct 15, 2010 | 2004 Acura TL

2 Answers

Replaced egr valve pressure sensor upstream and downstream oxygens sensors egr tube new egr valve new idle air control valve runs fine and idles fine one minute then starts idleing rough and dies starts...


r u gonna keep replacin parts-or do a scan 1st--not all problems show on a readout-like vacuum leaks or a failin computer--throttle body probly needs cleanin

Sep 06, 2010 | 1996 Ford Explorer

1 Answer

Rough idle hesitating at idle drives fine i


check plugs, wires, and coils for proper spark.

Oct 28, 2009 | 2002 Ford E250

2 Answers

How many oxygen sensors in a 2001 chrysler sebring 3.0


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Fig. Heated Oxygen (HO2S) location (sensor 1)-2.4L engine

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Fig. Heated Oxygen (HO2S) location (sensor 2)-2.4L engine

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Fig. Heated Oxygen (HO2S) location (bank 1, sensor 2) (bank 2, sensor 2)-2.7L engine

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Fig. Heated Oxygen (HO2S) location (bank 2, sensor 1)-2.7L engine

I hope help you with this (rated this help). Good luck.

Sep 09, 2009 | 2001 Chrysler Sebring

1 Answer

Replace oxygen sensors


these engines have 1 upstream o2 sensor and 1 downstream o2 sensor..the 1 in the rear exhaust manifold is the upstream and the 1 after the converter is the downstream..make sure you replaced the right one

May 15, 2009 | 1998 Plymouth Grand Voyager

1 Answer

Engine code p0421


Catalyst System Efficiency Below Threshold (Bank 1)

The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar. This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

A code P0420 may mean that one or more of the following has happened:

* Leaded fuel was used where unleaded was called for
* An oxygen sensor is not reading (functioning) properly
* The engine coolant temperature sensor is not working properly
* Damaged or leaking exhaust manifold
/ catalytic converter / exhaust pipe
* Retarded spark timing
* The oxygen sensors in front and behind the converter are reporting too similar of readings


To Do list

* Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
* Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
* Inspect the downstream heated oxygen sensor (HO2), replace if necessary
* Replace the catalytic converter

Jan 04, 2009 | 2001 Hyundai Sonata

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