1999 V70 121 kW Denso: front O2 sensor stuck at 0,5 V reading

MalteA · Post by **MalteA** » 29 Jul 2023, 06:47

Hey guys,

I am looking for a solution for a problem with the front O2 sensor readings. Reading through ECU (with Vida) is stuck at 0,5 V which equals lambda 1 or perfect air fuel ratio. Obviously this is not the expected behavior, since the signal should oscillate. Additionally I get the knock sensor high signal code (still original one). And fuel consumption is high, around 11,5 liters. Stalling at acceleration and fuel consumption might be caused by knock sensor fault. But the knock sensor in my opinion is triggered by the O2 sensor problem.

I swapped the O2 sensor for a denso one. Then my Volvo dealer said it needed to be Volvo original on this model. So I swapped a new Volvo branded one in. Still same problem.
Measuring the cable with sensor unplugged on the car side I get 12 V with ignition on II, 10,xx V when running hot. 0,6xx mV on the two signal cables.

Exactly the same as in this thread: viewtopic.php?t=81462

Unfortunately there is no solution mentioned. Does anyone have an idea what could cause the sensor signal to be stuck at a 0.5 V reading?

Best regards,

Malte

Post by **hausmeister** » 29 Jul 2023, 13:41

Hi MalteA
You could try to measure the signal that the ecu receives... maybe with a cheap oscilloscope.. maybe multimeter might work if it is fast?
I'd probably try to get a cheap used ECU and see if that fixes it. Just to eliminate that possibility.

MalteA · Post by **MalteA** » 29 Jul 2023, 23:40

Hi hausmeister,

I could get a ECU for 120€, but I would need to clone mine to the used one. And I have no clue how to do it. I believe there are people who could do it for around 120€. Not exactly the cheap version. Anyway, you are right and this would be the next logical step. My hope was that someone knows this exact fault since in the other thread the exact same problem was described.

Post by **hausmeister** » 30 Jul 2023, 01:43

Someone else might have better ideas.

Why do you need to clone it (except if there is a tune on it)? If it is the same partnumber, shouldn't it just plug in - at least for testing?

MalteA · Post by **MalteA** » 30 Jul 2023, 02:15

Since this is the ‘99 denso model the electronic immobilizer is part of the ECU. I didn’t fully understand it, but it is somehow tied to each individual control module/VIN. Which means you can’t just swap it in and out between different VIN.

xanthefin · Post by **xanthefin** » 30 Jul 2023, 04:10

MalteA wrote: ↑30 Jul 2023, 02:15 Since this is the ‘99 denso model the electronic immobilizer is part of the ECU. I didn’t fully understand it, but it is somehow tied to each individual control module/VIN. Which means you can’t just swap it in and out between different VIN.

IMMO3 module is married to ECM/ECU. You can't change it without removing marriage first (edit cloning is possible when knowing what to do).
New ECM needs be empty too of the marriage if i remember correct but i could be wrong of this part as IMMO3 module rules that but to do all this you need PIN code of IMMO3 module.
In my knowledge there is no other modules linked yet to IMMO3 system on V70 models up to 2000 year. There is VIN on CDM (dashboard) but it is not even connected to IMMO3 module so i don't understand any claims how it would work. Personally i think that is for VIDA detection just in software for diagnostics but some claims on internet it is too linked but then only way it would be is via ECM.

For the problem.. there seems be some good thread with similar problem.

Post by **hausmeister** » 30 Jul 2023, 11:13

sorry, I'm not up to date with the newer models/ecu/immobilizer.

MalteA · Post by **MalteA** » 21 Aug 2023, 02:02

Darkfleet (author of the mentioned thread) was so kind to describe the solution to his Problem in 2017: it was indeed a bad knock sensor and he changed it (without removing the manifold, heureka). From what he told me, it seems like the ECU freezes the oxygen sensor input (or ignores it), if the knock sensor delivers a code. Which theoretically makes sense to me. But... It didn't help me.

Actually the knock sensors for the Denso system seem to be out of production, nothing new available. I managed to find a used one and I put it in, without removing the manifold. You can't get a ratchet on the nut, so I did it without proper torque (it should be 20 nm and the right angle, around 4:30 pm?).

Bottom line: code cleared and didn't reappear within 50 km (which is not enough to say anything). But the problem with the oxygen sensor being stuck at 0,5 V persists.

Shoot.

MalteA · Post by **MalteA** » 21 Aug 2023, 02:04

xanthefin wrote: ↑30 Jul 2023, 04:10 There is VIN on CDM (dashboard) but it is not even connected to IMMO3 module so i don't understand any claims how it would work.

Those guys seem to offer a service I had in mind (swapping ECUs by cloning them): https://xemodex.com/us/available-servic ... -denso-p2/

Best,

Malte