Front O2 sensor heater resistance

[tony1968]

Related to my earlier post, which may be asking too much.

Does anyone know what the front O2 sensor's heater resistance should be? (Or have a spare 10 minutes to go and measure theirs!)

Old sensor was definitely broken as open circuit, now one was sold as "Genuine" but I suspect it's not. I measured resistance as 0 Ohms but my meter was complaining of low battery so if it's supposed to be very low I may have a false reading. I'd have expected about 5-10.

Oh, it's a non turbo 20002 V70 if that makes any difference.

Thanks.

[cheshired5]

I thought you had Vida?
Component resistances and terminal voltages are normally listed there so just look through the information section.

[tony1968]

I do, couldn't find a resistance value for the sensor itself. All I can see is the figure 2.32 Ohms when reading live data but this hasn't changed since installing new sensor or indeed with sensor unplugged.

If you know where to find it, please share.

I tried searching here but still no luck, which surprised me.

According to Vida he output from the new sensor looks sensible and a 21W bulb test shows the heater circuit active, yet it still keeps coming back with the preheating signal too high, as if it has a short. I think this would also be triggered if the sensor resistance was too low but don't know what too low would be.

I'd rather not buy another sensor just to compare.

[cheshired5]

Originally Posted by tony1968

If you know where to find it, please share.

All I know is that every component I've needed to check has been listed in the information section.
Not needed to look for an oxygen sensor though.

Vida also gives fix possibilities for every fault code so what does Vida say is the specific reason for your specific code?

[tony1968]

Found it. I was following fault trace but there's more in the information section. Specification says 2.4 Ohms +- .24 at 20C.

The design section says it starts very low, rising to approx 2 Ohms at normal operating temperature.

If I remove the sensor from the manifold it gets hot and Vida shows it pulling about 1.8A after a few seconds. With it in place it drops over a few seconds to around -.04 . Seems sensible to me.

With a 21W bulb in place of the sensor My ammeter and Vida both record about 2.2A and the bulb glows brightly.

No matter what I do, Vida reads 2.32 Ohms. I'd expect to see this change as the sensor warms up. If this is correct (or at least what the ECM thinks) it shouldn't error because that's well within tolerance.

With a fresh battery my multimeter now measures 0.4 Ohms cold - 0.6 hot. I'm going to try to borrow a neighbour's meter to eliminate a false reading from mine.

As for following Vida's fault finding I'm stuck when it starts referring to plugging in the breakout box and measuring specific pins.

[cheshired5]

What's the specific fault code(s)?

[tony1968]

ECM-2110 Front Heated Oxygen Sensor (HO2S), preheating - signal too high.

Made a reading error on my meter - it's 4 Ohms, not 0.4, get same result with next door's meter. That's quite a way off spec, would it be enough to cause the fault?

I wouldn't mind if I'd decided to try a universal one but this was sold as genuine.

[cheshired5]

Originally Posted by tony1968

it's 4 Ohms...... That's quite a way off spec, would it be enough to cause the fault?

If I'm looking at the right data from the limited vehicle info, it's slightly out of spec not a way off.

[tony1968]

Yeah, that's the page I was looking at. I thought it was a way off because the spec states a 10% tolerance, mine's about 70% over. My hot measurement (well, taken within seconds of stopping the engine) is 100% over.

On the other hand I agree it's only 1-2 Ohms over, I just wonder if the ECM thinks it's to far out and that's why the error keeps coming back.

I'm also puzzled that when I read live data the resistance remains at a steady 2.32 Ohms, yet the current starts high and drops as expected so it's managing and measuring that.

Wife thinks I should give in and take it to a local garage. I think that without Vida they'll be in a worse position than me and will just start fitting new bits until the code goes away.

So, if the sensor resistance is OK and I've proved the circuit is operating when it should and capable of supplying enough current what else can I check? I did remove and reseat the ECM so I could check for corrosion etc and in the hope that sometimes that sort of thing helps!

[tony1968]

Right,

I've had the ECM out today and checked the wiring from the ECM connector to sensor. All connected OK, no shorts to ground, earth or other wires. Heater resistance measures the same from the connector pins.

So the only thing I haven't done that Vida recommends is confirm the heater resistance is about 1 Ohm at 20C (Mine's 4 at whatever the weather was this afternoon). So that would seem the obvious fault except this is a "high" error, associated with a short to power or very low resistance.

Vida live data still shows constant 2.32 Ohms.

As an aside I now know why my cruise control doesn't work - clutch position sensor moves smoothy to about 40%, then jumps to about 75 and stays there. So, not a total waste of time.