MY2000 V70 2.4 Lambda Issue

[topsie]

Morning all,

Hoping for a bit of help identifying an issue with my 2000 V70.

It's running the DENSO ecu and is throwing a code for o2 sensor heater circuit malfunction. The o2 sensor is getting 14.4v (engine running) at the heater and has good continuity between the o2 sensor ground and the ECU.

I thought I had a poor MOSFET, which I have replaced on the ECU.

The heater circuit is working - it grounds through the ECU and I can see that it pulls 1-1.5A for about 10 seconds. However, it then opens the circuit.

I see no change on the B1S1 voltage, even if I ground the o2 sensor to bring it up to temp manually.

I'm using a generic BOSCH sensor (the original is open circuit on the heater) but have also tried a post-cat OEM DENSO sensor. I'm reluctant to simply buy another DENSO as they aren't cheap and I'm not convinced the o2 sensor is at fault.

Any help appreciated.

Nick

[topsie]

So I've been doing a fair bit of testing and here are the results:

Reading live data, the b1s1 o2 heater resistance is always 2.32ohms. This is regardless of what is actually connected to the heater circuit. Be it open circuit, a 5w resistor or a indicator bulb. The o2 heater element current is also always 0.00mA. Lambda remains at 1.000.

The error code is: ECM-2120 FRONT HEATED OXYGEN SENSOR (H02S), CONTROL ELEMENT.

What doesn't help is that is appears this code is for both the sensor and the heater. Awesome work Denso!!!

Im going to bite the bullet and buy a genuine denso o2 sensor. I've got zero confidence this is going to resolve the issue, but happy to find out and report back here.

I've seen a couple of posts of similar models where the ECM has required replacing. I'm hoping that's not the case, but not particularly high confidence this isn't the issue.

[Luxobarge]

Originally Posted by topsie

Reading live data, the b1s1 o2 heater resistance is always 2.32ohms. This is regardless of what is actually connected to the heater circuit. Be it open circuit, a 5w resistor or a indicator bulb. The o2 heater element current is also always 0.00mA. Lambda remains at 1.000.
.

I'm struggling to understand this. How are you obtaining those readings? If you're using diagnostics, then Lambda will be 1 because it's probably in "limp" mode, therefore substituting default values in the presence of a critical error. Probably same goes for those other readings too - all default values.

If it were me I'd be going back to basics and using a multimeter to measure the resistance of the sensor heater at the connector plug, if it's dead short or open circuit (more likely) then there's your fault. I'd expect something between 2 and 10 ohms for a working heater circuit, maybe others here will know exactly what the reading should be.

You could also check the feed voltage with a meter to make sure you've got a decent 12V-ish feed.

When I've had an O2 sensor heater fault that's all I've done, I found I had a good 12V feed and open circuit heater at the sensor end, so replaced the sensor and it was all good.

You could also rig up the multimeter in series on a current setting to see what the heater is drawing, but more fiddly and not going to tell you a great deal more than checking the heater resistance IMHO.

I suspect that the ECU going into limp mode is giving you your confusing readings if you're using OBD diagnostics to provide that information, do it old-school with a multimeter and I reckon you'll get more sensible information.

Unless I've *completely* misunderstood what you're doing!

[topsie]

Sorry, I could have been a bit more descriptive on what I've checked to date.

Good continuity between the ground pin from o2 sensor harness back to the ECM connector block.

Good 14.4v feed to the heater with the ignition on iaw wiring diagrams.

Pre-Cat Bosch Universal Lambda Sensor (Both pre and post cat sensors were replaced by previous owner) heater circuit has a resistance of 2ohms @ 15c.

Original pre-cat DENSO lambda sensor heater is open circuit. (Which tracks with the fault)

Original post-cat DENSO lambda sensor heater measures ~2ohms @ 15c

I've tried fitting the post-cat DENSO sensor in the pre-cat position. No difference.

I've tested the heater circuit on both the BOSCH replacement and DENSO post cat sensors. (do they get hot when out of the car?) Both function.

Even with a faulty heater circuit, you would normally expect the sensor to start providing a reading on fast idle & once up to operating temp. What it's actually doing is nothing.

My thinking is that either I'm chasing the wrong fault as I'm not using VIDA and the fault code being shown is a generic pre-cat sensor code with a replacement DENSO sensor being the key (I'm aware that these can be sensitive to the wrong sensor) OR the ECM is breaking down with age and I'm wasting my money buying a DENSO sensor.

What I expected to happen by replacing the heater element circuit with a turn signal bulb, is for the error to shift from the heater (as it now has an appropriate and proportionate load) to the sensor voltage being low / high / open / short. Again, nothing...

I just don't want to waste ~£100...

[Baffler]

Originally Posted by topsie

My thinking is that either I'm chasing the wrong fault as I'm not using VIDA and the fault code being shown is a generic pre-cat sensor code with a replacement DENSO sensor being the key (I'm aware that these can be sensitive to the wrong sensor) OR the ECM is breaking down with age and I'm wasting my money buying a DENSO sensor.

Indeed, without VIDA you may not see other hidden codes. Do you know anyone in your area who could assist with VIDA and DICE?

I'm no expert on these, Luxo is far better read on the subject, but what is glaring out at me is that generic Bosch pre-cat sensor on a Denso system. Personally I would be replacing this with a genuine Volvo sensor as the generic Bosch one may be trowing the post-cat Denso sensor. As you say these are sensitive to the wrong sensor, some have got lucky, others not so lucky.

Are you able to clear/erase the codes? If so, once the codes are erased, reset the ECU values by disconnecting the battery (leave overnight or join both leads together for 10 minutes), reconnect and take it for a drive to see what codes return.

[topsie]

I've got the correct DENSO sensor coming Monday - I'm not convinced but more than happy to be proven wrong!!!

[topsie]

Well I'm happy to swallow my pride.

Denso sensor fitted and everything's behaving as expected. With any luck the Cat is healthy and it'll pass its MOT retest.

Thanks all for the help. Lesson here is don't mess around with Lambda sensors from otjer manufactures, stick to the OEM part.

[Luxobarge]

Nice one, well done and thanks for posting the result. I had more confidence that the sensor would fix it than you did I think!

Cheers

[Baffler]

That's good to hear, Topsie, glad to read you got it sorted!

Do you happen to have the Denso part number to hand and the Volvo p/n you referenced from? Would be good to have it for other readers of this thread and future reference.

Get your CAT nice and warm on the journey to the test by keeping the revs high and selecting a lower gear. It's a massive thing on the 2.4 so it should fly through the emissions test.