Safe to Drive 2006 V70 NA with failed rear O2 sensor heater ?

[Mike98]

I was planning to drive my 2006 V70NA on a 1000 mile trip starting later this week. Over the weekend the check engine light came on and the cause was pending fault code P0036 followed by active fault code P0037. Both of these codes indicate a problem with the heating element in the downstream O2 sensor. I removed the original factory Denso sensor from the cat and confirmed that the heating element has failed (open circuit - infinite resistance). According to Vida the rear O2 sensor heating element should have 2.4 ohms resistance at room temperature - same resistance as the front sensor.

More than one downstream O2 sensor part number was used on 2006 V70s, depending on the chassis number and factory code.

The factory installed downstream sensor on my car is Volvo PN 30650090, made for Volvo by Denso. FCP Euro shows this part as only being available from Volvo, there is no OE equivalent unit available from USA Denso distributors. European Denso distributors cross reference 30650090 to Denso DOX-0404 but I have not found any USA sources for DOX-0404. Looks like the only choice is to purchase a 30650090 from Volvo and wait a couple of weeks for delivery.

The Denso web site indicates that a Denso 234-4450 (also known as DOX-0402) is correct for a 2006 V70 NA. A 234-4450 was in stock at AutoZone so I purchased it. It looks identical to the 30650090 that came on my car but a heater resistance measurement shows 12 ohms instead of the 2.4 ohm specification in Vida. I suspect that if I install this sensor, the heater wont work properly, there will be heater fault codes and I wont be able to return the $160 part to AutoZone because it is used. Probably the 234-4450 / DOX-0402 sensor with 12 ohm heater was intended for "always on" operation instead of the PWM control that must be used for the 30650090 / DOX-0404 2.4 ohm heater.

Question 1: Does anyone have a used good Volvo/Denso 30650090 rear O2 sensor ? If you do, could you measure the heater resistance (two black wires) and confirm that it matches the Vida 2.4 ohm specification ?

Question 2: Does the rear O2 sensor have any effect on the closed loop air/fuel mixture or is the sensor just there to check the cat performance ? Could the cat be damaged by driving 1000 miles with a rear O2 sensor that works but doesnt have a heater ? If there is any possibility of damaging the cat i wont drive the car until the sensor is replaced.

Thanks,

Mike

[abscate]

The rear sensors indeed just monitor cat performance. Take the trip and fix whenyou get back.

[Mike98]

I am slightly worried that the failed heater in the downstream sensor will cause it to report incorrect data due to the sensor running at lower than normal temperature. I have read that some ECUs use the downstream O2 sensor data to optimize the cat performance, perhaps by tweaking the Air/Fuel ratio target for the closed loop controller that incorporates the wideband front O2 sensor. If the V70 2006NA ECU doesnt do that, then the rear sensor should have no effect on the closed loop control ?

Thanks,

Mike

[jonesg]

from what I've read the heater is only to get the sensor up to functional temp faster.

[volvolugnut]

from what I've read the heater is only to get the sensor up to functional temp faster.

That is my understanding - Heater is only to get cold start temp of cat quickly raised so it can effectively trap emissions.
volvolugnut

[abscate]

The heater on the oxs only heats the sensor , not the cat. The cat gets hot in the act of “ catalyzing”

The sensor needs to be heated , if I remember right, to keep a precise reference voltage for feedback. The potential generated by the OXS is temperature equation ( Nernst?) so the heater ensures the data is good

On edit - incorrect, fixed below. Function is VIN dependent

[Mike98]

Bad News: I ordered a 30650090 downstream O2 sensor from Tasca and got this reply:

"Part #30650090 is currently on national backorder with the automotive manufacturer and has no estimated date of resupply. We do not currently have this item in stock at our warehouse and are unable to acquire it at this time. Unfortunately, despite our best efforts, sometimes the demand for certain parts and accessories exceeds manufacturers’ current supplies. I apologize for the inconvenience."

Is it possible that someone on MVS has a a good used spare #30650090 ? I could place a "Want to buy" request in the MVS Classifieds forum ? The sensor was only used on some P2 non-turbo with Denso engine management.

Denso and US suppliers such as AutoZone list a Denso 234-4450 sensor as compatible, but they are incorrect. 234-4450 has a 12 ohm heater (I measured it). 30650090 has a 2.4 ohm heater according to Vida. I bought and returned a 234-4450 without installing it.

Thanks,

Mike

[dikidera]

The rear sensors indeed just monitor cat performance. Take the trip and fix whenyou get back.

Actually no, since for the NA engine I have reverse engineered quite a lot of code. It does actually provide additional feedback for fuel mixture. That is to say that the signal from the rear o2 helps to stabilize, further optimize the front oxygen sensor signal to finally calculate fuel mixture.
However this doesn't mean that is that important, only that it helps, but it's role is much smaller than it seems.

[RobsS40]

My $0.02- I've had pretty good luck substituting O2 sensors. In fact I did so on my '06 S40 2 years ago and it seems fine, runs well, no ECM problems or error codes, exhaust is pretty clean smelling for 186K miles. But I admit I did it not knowing about the 2.4 ohm heater and PWM control.

I assume you checked fuses (?).

Someone on ebay has 2 of the 30650090 right now.

[poto993]

ok good.