O2 sensor connections swapped what happens when upstream for down, and down up?

[captainkephart]

Hi,
I've had endless versions of the O2 / Lambda sensor fault light problems.
No garage seems to fix it - or even understand what is wrong (Xsara Picasso 1.6 DOHC petrol 2008).

I suddenly thought - the O2 sensor plugs and sockets are interchangeable, not colour coded and the trailing socket leads are very close - so easy to plug the wrong way round - upsteam to down socket and down to up.

What happens if you do that? Might it explain why I keep on getting 'P0130 - O2 Sensor Circuit'?

When I've changed sensors (twice) I have just copied the plug / socket arrangement as I found it - but what if a previous garage mixed them up?

Crazy 'plem-plem' idea? Any suggestions advice welcome.

Take care all, and thank you for the best car forum on the Internet!
Ciao, Captain K

[wheeler]

Are you sure about the plugs? They are normally different colours to avoid mixing them up & the plugs are keyed differently to physically stop you doing it. Has someone ‘modified’ the wiring.
Event if you did switch the connectors as as soon as the ECU came out of open loop it would throw a wobbly & put on the warning lights.
You need to look at live data from the sensors to start tracing the fault.

[captainkephart]

Hi Wheeler,
Thanks for the suggestion.
Yes, absolutely sure about plugs being interchangable.
Original wiring. The sensors (I've had Bosch, NGK) have the standard 4-wire white / grey / grey / black wires.
On the car / ECU side, I haven't looked at wire colours yet to see if there is a difference ...

I'm asking the question as a theoretical 'what if' to understand how ECU / fuel system wiould react to such a condition - maybe to help others (that's why the subject line is general).

I didn't want to get into the specific situation with my car too much. Full saga (one part you have seen) here:
viewtopic.php?t=64136

Recent live data shows almost continuous lean condition ... previously (before changing both O2 sensors to NGK) car was flipping into limp home / super rich mode.

Thanks, Captain K

[captainkephart]

Hi,

So here is how the oxygen sensors are wired up at the moment.

I've no idea if this is the right way round ... does anyone have a wiring diagram for this car please?
In my Haynes manual for this car it has all the wiring diagrams for the body systems - but not for the engine ECU!

(The Haynes for my older car, to 2001, does have them, but the colours are different - doh!).

The socket tails are slightly different lengths, just an inch / few cm or so ... the longer one is going to the upstream sensor (on top of the exhaust manifold).

Suggestions? Thank,
Captain K



<< Citroen_Xsara-Picasso_Lambda-O2-sensor-wiring.jpg >>

[wheeler]

If you PM me your reg number I will get a wiring diagram. PSA dont go by wire colours, they use codes printed along the wires for identification hence the reason any diagrams you have seen may have different colours. The codes are usually between 2 & 6 digits & can contain both letters & numbers. On the oxygen sensors they will only likely be on the ECU side of the harness, the sensor side wires on O2 sensors dont normally have them. The codes will be along the lines of 1351C & 124.

[wheeler]

OK This should be the injection diagram for your engine.
1350 is the upstream O2 sensor 1351 is the downstream. The codes shown on the wires should confirm if they are the correct way around. The codes are printed every couple of inches along the whole wire so you can check up at the ECU plugs too. They all go to the 48 way Brown connector on the ECU. Be aware that the wire may be a different colour at each end, this is why we always go by the code. There wont be any codes on the black, grey & white wires going into the sensors, only from the 4 way connector towards the ECU.
You can also do a resistance check on the heater elements of the sensors (pins 1 & 2), the spec varies between brands of sensor but usually between 3 - 11.1 ohms, Bosch & Delphi should be the higher end.
EDIT: Just a thought, have you disconnected the ECU & checked for water ingress? Its not uncommon on the Xsara Picasso due to where it is located & can cause loads of different faults.
There should be a plastic boot over the plugs which is sometimes not there (or poorly fitted) & there was also a modification to re route the wiring downwards.

[captainkephart]

Hi Wheeler,
Superb ... OK, I'll check.
I assume you have a stack of the real engineers handbooks somewhere ... very useful!

Just to summarise, in general terms, if the sensors are connected the wrong way round, then, nothing much happens ...
until the engine warms up (comes out of open loop to closed loop) and the ECU starts reading the sensor data. ECU recognises the wrong data pattern(?) and says oops, Engine fault. No damage, no disaster? Is that correct ... ?

ECU plugs, thanks, I checked them last year, there was brake fluid in the middle one (a few mm). Might it have corroded the pins? Could that explain all the inconsistent problems I've been having? Took several goes to clean it out with the alcohol they use on PCBs.

[I think the brake fluid came from when the previous owner had it in the garage for n/s serious wing damage repairs, so the oil would've been in there at least a year].

After that I reset the BSI too.

Thanks again, Captain K

[wheeler]

Just to summarise, in general terms, if the sensors are connected the wrong way round, then, nothing much happens ...
until the engine warms up (comes out of open loop to closed loop) and the ECU starts reading the sensor data. ECU recognises the wrong data pattern(?) and says oops, Engine fault. No damage, no disaster? Is that correct ... ?

Pretty much, it will then likely ignore the readings from the sensors & run on default values.

ECU plugs, thanks, I checked them last year, there was brake fluid in the middle one (a few mm). Might it have corroded the pins? Could that explain all the inconsistent problems I've been having? Took several goes to clean it out with the alcohol they use on PCBs.

If I remember right the middle one is the 48 way brown plug, the same one the O2 sensor wires terminate in, that's definitely worth a closer look, may even be worth opening the ECU case. I have no idea what brake fluid does to a PCB?

[captainkephart]

Thanks again for the clarification.

Brake fluid's no good for your car body - so obviously corrosive in some way ... anyone else know?

I did open the case last month - tricky but doable with care - no oil or water inside (which is good as it would be a nightmare to clean - bazillions of little soldered joints - it's a full up computer in there!).

If anyone is brave enough to try (you have to be very VERY careful - a slipped screwdriver and you're 600 quid out of pocket!, here's a professional video:



Thanks, Captain K

[Paul-R]

Wow! You need a big set of balls to be prepared to delve inside an ECU. And some quite expensive equipment once it's open.

[captainkephart]

Hi Again,

Well, I tried to check to codes on the wires from the sensor plugs to the ECU.
Most have nothing (rubbed off?), there's one wire with a row of spots. That's all. At the ECU on the three big plugs, yes some wires have dot-matrix style numbers; some nothing, some a row of dots ... so stuck.

Still have the unresolved 'did the brake fluild in the ECU sockets corrode the pins' issue. Incidentally, other sockets in the area (eg engine temp sensor, oil pressure) also had brake fluid in them ...

I think somthing is deteriorating because having had a series of lambda-sensor related messages in the past, but since spring have been getting only: P0130 - O2 Sensor Circuit (cleared several times).

And today: P0134 - O2 Sensor Circuit No Activity Detected
I've cleared it twice today and it has come back within a few miles (engine at working temperature).

Beginning to sound terminal? I've no idea what to try next. Any ideas?
Thanks, Captain K

------------------------ DATA follows -----------------------
Here's the Live Data grid after the first Fault Light today for P0130 - O2 Sensor Circuit (parked up, engine running):

Description Value Units Min Average Max
03 - Fuel System Status
Fuel System 1 open loop fault - 8.00 8.00 8.00
Fuel System 2 Not Reported - 0.00 0.00 0.00
04 - Calculated Load Value 27 % 26.27 26.86 27.06
05 - Engine Coolant Temperature 92 °C 92.00 92.00 92.00
06 - Short Term Fuel Trim - Bank 1 0.0 % 0.00 0.00 0.00
07 - Long Term Fuel Trim - Bank 1 1.6 % 1.56 1.56 1.56
0B - Intake Manifold Absolute Pressure 35 kPa 34.00 34.75 35.00
0C - Engine RPM 745 rpm 738.00 746.31 756.75
0D - Vehicle Speed 0 km/h 0.00 0.00 0.00
0E - Ignition Timing Advance for #1 Cylinder 5 ° 5.00 5.83 7.50
0F - Intake Air Temperature 37 °C 37.00 37.00 37.00
11 - Absolute Throttle Position 18.8 % 18.83 18.83 18.83
14 - Bank 1 - Sensor 1
Oxygen Sensor Output Voltage 0.000 V 0.00 0.00 0.00
Short Term Fuel Trim 0.0 % 0.00 0.00 0.00
15 - Bank 1 - Sensor 2
Oxygen Sensor Output Voltage 0.040 V 0.04 0.04 0.04
Short Term Fuel Trim 99.2 % 99.21 99.21 99.21
21 - Distance Travelled While MIL is Activated 0 km 0.00 0.00 0.00
47 - Absolute Throttle Position B 18.8 % 18.82 18.95 19.22

----------------------------- Freeze Frame ----------------
This is the second time the light came on (sorry didn't capture the Live Data Grid):

Description Value Units
P0134 - O2 Sensor Circuit No Activity Detected
03 - Fuel System Status
Fuel System 1 closed loop -
Fuel System 2 Not Reported -
04 - Calculated Load Value 42 %
05 - Engine Coolant Temperature 81 °C
06 - Short Term Fuel Trim - Bank 1 25.0 %
07 - Long Term Fuel Trim - Bank 1 0.0 %
0B - Intake Manifold Absolute Pressure 46 kPa
0C - Engine RPM 2427 rpm
0D - Vehicle Speed 83 km/h

[wheeler]

Hi Again,

Well, I tried to check to codes on the wires from the sensor plugs to the ECU.
Most have nothing (rubbed off?), there's one wire with a row of spots. That's all. At the ECU on the three big plugs, yes some wires have dot-matrix style numbers; some nothing, some a row of dots ... so stuck.

Your not looking hard enough then, I just don't believe that out of 8 wires none of them have any readable codes. The bits with exposed insulation can be a bit grubby & sometimes needs a bit of a clean with a solvent. The codes are printed along the entire length of the wire every few inches or so. Sometimes you need to peel back some of the insulation tape a few inches to get a better view, the bits under the insulation tape are normally quite well preserved, again wipe off any sticky residue.

[captainkephart]

Hi Wheeler,
OK, must try harder indeed ... obviously didn't strip back far enough. Didn't use solventy as thought might remove the codes ....
[Need some sort of futuristic spider drone to climb in where very hard to get at!]

Any thoughts on what "P0134 - O2 Sensor Circuit No Activity Detected" generally means?

Thanks again ...
Captain K

[wheeler]

Any thoughts on what "P0134 - O2 Sensor Circuit No Activity Detected" generally means?

What it means is further investigation is required to why there is no activity detected, unfortunately fault codes most of the time don't tell you what's wrong, only where to start looking. Where I would start looking is checking the wiring between the O2 sensors & the ECU.

[GiveMeABreak]

Any thoughts on what "P0134 - O2 Sensor Circuit No Activity Detected" generally means?

Wheeler already answered before I posted ^

Generally, this fault refers to regulation of the upstream oxygen sensor is at the limit (weak sensor) and voltage of the upstream oxygen sensor higher than 0.3V. So has to be a dodgy sensor or the electrical wiring / connections are damaged / shorting / faulty.