I replaced both O2 sensors on a 96 Jetta, and the engine check light will come back on after a couple days. I had the auto parts store reset it, and it says bank 1, PO131, upstream sensor.

Any ideas on why it keeps coming back on despite having new sensors? I also put on a new MAF, as the voltage reading was a bit low. Not unless the sensor could be junk?

They were direct replacements, not spliced in.

Unhook the battery for an hour or more.
See if it clears the persistent codes.

Parts stores , or generic code tools do not clear the persistent codes.
Could also be a leak in the flex pipe or gasket at the head.

Rich

Thanks for the reply. I'll try that and see if it helps.

From The Ross-tech wiki:

16515/P0131/000305
Contents

1 16515/P0131/000305 - Oxygen (Lambda) Sensor B1 S1: Signal too Low
1.1 Possible Causes
1.2 Possible Solutions

16515/P0131/000305 - Oxygen (Lambda) Sensor B1 S1: Signal too Low
Possible Causes

Wiring to Oxygen (Lambda) Sensor Bank 1 Sensor 1 faulty
Oxygen (Lambda) Sensor Bank 1 Sensor 1 faulty

Possible Solutions

Check Wiring to Oxygen (Lambda) Sensor Bank 1 Sensor 1
Check Oxygen (Lambda) Sensor Bank 1 Sensor 1
Perform Aging Check

What brand is the sensor you used? What part number? What engine family? Bosch sensors work well, others less so. Many brands fail to conform to the rather restrictive maps used in VW ECUs. This is an OBD 2 car, and generally speaking, disconnecting the battery (you also need to make extended contact between the (+) and (-) cables while they're off the battery) won't clear the stored codes.

The Cap'n

Upstream from Rockauto

ULTRAPOWER Part # 2344663 One of our most popular parts
[Flag indicates this part fits vehicles sold in the US Market. It does not indicate where the part was made -- manufacturers produce parts in multiple factories worldwide.] [Flag indicates this part fits vehicles sold in the Canadian Market. It does not indicate where the part was made -- manufacturers produce parts in multiple factories worldwide.] OE QUALITY REPLACEMENT SENSOR - UPSTREAM - USA - FROM CHASSIS #1H-T-000 001; WOLFSBURG EDITION

and downstream from Evil Bay

Not sure if it is true or not, but was also told that the upstream and downstream are interchangeable??

Like this one mentions it can be used in the upstream or downstream position??

http://www.ebay.com/itm/New-O2-Oxygen-Sens...6fd&vxp=mtr

I'm not exactly sure what you want me to do with two disconnected cables? Are you saying to disconnect the two cables, and join them together again aside from the battery to clear the codes??


This is an OBD 2 car, and generally speaking, disconnecting the battery (you also need to make extended contact between the (+) and (-) cables while they're off the battery) won't clear the stored codes.

The ECU has memory.
It has stored power that will take about 30 minutes to drain.
Touching the cables together might speed up that process, might not.

I just pull the battery and wait an hour.

I don't believe it's really OBD2.
This is not from a 40 year tech like the cap'n, just a vw guy who does not believe that vw implemented ALL of the obd2 protocol until 2000.

My 98/99 cabrio works when you pull the battery, or use VAGCOM to clear the persistant codes...
Can't do that with a standard reader because VW did not adhere to the OBD2 specification .....they just did a bit of it...same with audi.

I have had shit luck with anything but OEM O2 sensors on vw....just the way it is.

I have had leaks in the upper flex pipe that causes the front one to have a weak reading that will throw that same code.

Again...not the cap'n....he has done tons more of these.

Check the sensor with a volt meter cold and when running hot, then when it throws the code....
Should be .5 to 1 volt range I believe.

Far as I know, it is OB2, but then again, I wouldn't know if it was implemented all at once or not?

I just unhooked the positive cable is all? Plan on leaving off over night.

What would be the looks, if in fact it was the flex pipe. This thing has 164,000 miles and counting.....

Yes, touching them together discharges the capacitors in various units. However, this "usually" only works for OBD1 cars.

But won't hurt anything if I do, correct?

Not parts I would ever buy, nor advice I would take. And they're NOT "OE quality". There's obviously a reason VW specified 2 different parts for the system, and Bosch made them that way. Cheap they are, but cheap isn't always inexpensive. Now you have a problem, they're unlikely to return your money, and buying the right parts is gonna cost you a bunch more. As I said before, many aftermarket parts don't operate in a way that conforms to the maps in a VW/Audi control unit. While they may meet the numbers, beginning to end, they often don't move from one end of the spec to the other in a manner (call it a "curve", if you will) the CU is looking for. I see this A LOT...... Aftermarket converters, especially for VW/Audi cars, which meet the full spectrum of tests set forth by the CA Air Resources Board (and now used by a number of other states), inevitably trigger the CEL, sometimes right out of the box, always within days. The solution? OE converters. Same for coolant temp sensors, thermostats, and even coolant. Gotta use the real thing or you're likely to be seeing a comeback. The latter list not so much on your car, but it gets bad after 2000.

The Cap'n

Not as long as they're not connected to a "live" battery (one still connected to both cables).

I wonder if this would be a good source for getting them without compromising quality?

http://www.germanautoparts.com/Volkswagen/.../Exhaust/152/11

O2 sensors.

Just find the Bosch part number, then shop around for that specific part.

I know I have two replacement O2 sensors on the shelf..
I went for the cheap ones, they tested fine, but they did not satisfy the VW ECU.

Went back to OEM Bosch sensors and all was fine once I reconnected the battery...no more CEL issues.

You will chase your tail on this one, just suck it up and buy the Bosch sensors.

rich

The front sensor (B1-S1) is #15 024, the rear (B1-S2) is #15 160.

The Cap'n

There's a bunch of numbers printed on it, but I don't see any of those numbers, at least on the one sensor?

It is a 1996 VW Jetta, 2.0

http://www.amazon.com/Bosch-15024-Oxygen-S...r/dp/B0074O7TL8

http://www.amazon.com/Bosch-15160-Oxygen-S...t/dp/B000BZI3H6

The numbers I gave you are the correct ones for your car.

The Cap'n

The #s Cap'n provided are right in the URLs you posted

Well hopefully this is what my car is going to like, but I got them ordered.

No engine check light after a week of install, and so looks like the problem is solved, except for one little bug that has been there since about 5 years after it was purchased new, and that is some screwy bug that is intermittent. Usually on a cold engine, if it is going to happen, it is usually within the first 5 minutes, it may happen once a week, or once a month, but the idle with go from about 500 to about 1200 for about 5 seconds, and if you let it go, then the idle will go to about 1200, and then come down to normal, or if you jab the accelerator, and quickly let off, it will clear it out, and idle normal, and so I don't know what would be causing that particular problem, but for no more than what it happens, may not be worth pursuing.