Oxygen sensor code C3 picasso

[Ddclutch]

Another code fault on my C3 Picasso (petrol 1.6l)
This time the reader shows:
Downstream oxygen sensor resistance too high

I suspect this refers to the lambda sensor on the exhaust pipe, and there is perhaps a break in the wiring, hence the 'resistance too high' fault. Does this sound right?

Looking at it, the wires to the sensor are exposed and all twisted up, likely damaged. Whoever fitted it didn't 'unwind' the wires before screwing it in to the exhaust. Poor work, considering I know the previous owner and the car has only ever been worked on by the same main peugeot/ citroen dealership.

[GiveMeABreak]

There are 2 sensors; upstream and downstream, but these like any sensor has a finite life, so depends on your findings.

[Ddclutch]

Yes,this says its the downstream sensor.

The question was really, would a break in one of the wires throw a report of "resistance too high" or would it simply not function and give a different code.
This shows P0054 but that may be too generic to say.

[GiveMeABreak]

Fault Code:	P0054
Description of Fault:	Downstream oxygen sensor resistance fault: Resistance too high. Detection of a problem with the downstream oxygen sensor heating: Resistance internal to the downstream sensor is too great (For more than 6 s) Conditions of activation of the diagnostics The following conditions have to be met: - Engine management ECU in main triggering phase - Temperature of the exhaust gas at the downstream oxygen sensor between 200 and 539°C - Engine off for more than 3 minutes - Inlet temperature higher than -6.8 °C - Battery voltage between 10.7 and 16.1 V - engine running - No cutting of injection
Conditions for Fault to clear:	Resistance internal to the downstream oxygen sensor less than the maximum threshold (For more than 20 s)
Downgrade Modes whilst Fault is active:	Transition to open loop of the downstream regulation Deactivation of purging of the catalytic converter Switching on of the warning lamp and/or warning message: Warning lamp MIL
Symptoms:	Emissions outside the norms
Suspect Areas:	Downstream oxygen sensor Electrical harness

[ozvtr]

Both oxygen sensors have heaters to speed up the initial operation of the sensors. The heater is independent of the sensor element itself.
In your case the engine ECU has detected a lack of continuity (resistance too high) in the down stream (post cat) oxy sensor heater circuit.
Could be the wiring, a connector or, most likely, the heater element.
The sensor element (and consequently the engine) will continue to function just fine without the heater. But until it's fixed, the engine light will remain on.

[Ddclutch]

Thanks, helpful table, Marc. Though I don't fully understand all of the entries there.

I cleared the code and then went out this afternoon. Local roads, about 45 miles and the mil didnt come back on again. Not yet anyway, though from past performance it will.

The initial history of this was the mil coming on and fault code relating to the oil temp/ level sensor. I replaced that sensor and that fault code hasn't returned. But perhaps it had been masking this P0054 one.

I now see I am also getting a 'Heater resistor bank I sensor' code P0054$07E8 code. Does that shed light on this as well?

The other thing is the engine is prone to snatching, or stumbling when accelerating from low revs. A low speed misfire. Could be poor fuelling if the lambda sensor is playing up.

[CitroJim]

Yes, it very much looks like the sensor heater is duff and as it cannot get hot enough to give a valid signal it may well be causing your engine stumbles..

Time, if you are sure the wiring to it is good, to replace it.

[Ddclutch]

Thanks. I presume the heater is an integral part of the oxygen sensor unit then?

Just another thought, when the oil level sensor failed a few weeks ago, the error code said something about not registering because temperature not being in range. Seems a coincidence - could the two faults be related? e.g. Low battery? ( there are no other indications of a poor battery, it always starts well)

[CitroJim]

Yes indeed, the heater is an integral part of the sensor as it needs to be very hot to work correctly. Around 800 degrees I believe...

A low battery on vehicles with complex electronics like the C3 Pic can cause all sorts of bizarre behaviour so definitely worth a check...

[GiveMeABreak]

Thanks, helpful table, Marc. Though I don't fully understand all of the entries there.

I now see I am also getting a 'Heater resistor bank I sensor' code P0054$07E8 code. Does that shed light on this as well?

This is the same fault (P0054) for which the table has highlighted the resistance being too high.

I doubt very much it is the heating power supply on Pin 1, because the power is supplied directly from the engine ECU and the same wire supplies the following components, so you would have other faults if the supply wire was compromised. I suggest you change the sensor.

Proportional Oxygen Sensor (1357)
Canister Discharge Electrovalve (1215)
Oil Breather Re-Reat resistor 1 (1273)

Pin Wiring Assignments
Pin 4 = 1302: Signal from lambda sensor C (+) downstream of the catalytic converter
Pin 3 = 1303: Signal from lambda sensor C (-) downstream of the catalytic converter
Pin 2 = 124: Control heating lambda sensor C downstream catalytic converter
Pin 1 = 1351B: Lambda sensor heating power supply

[Ddclutch]

Thanks Marc. Looks like the heating component of the Lambda sensor then.
Full code report:

P0054$07E8
HO2S heater resistance bank 1 sensor
2

(I think that means sensor 2, even though the 2 shows below on the next line. Its just the screen width)

And Jim, thanks. I will check battery volts, engine off and when running. Though the starter spins really well so there's no indication of a sluggish battery.