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

[captainkephart]

Hi Wheeler / Marc,
Thanks, that's most heplful!
Interprepting codes is like dealing with an exam algorithm (sorry, probably not funny).

Upstream sensor was brand new NTK out out of sealed packaging and fitted end June (as error then was P0137 - O2 Sensor Circuit Low Voltage and P2191 - System Too Lean at Higher Load). Fine after that till end July when got this stream of 'O2 sensor circuit' faults mentioned above.

What could be killing the O2 sensors? I wondered if it could be head gasket leaking slightly (I did check the head bolt torques, 4 of the rear 5 bolts were not to spec, OK now). I (and two garages) have now put in 8 new O2 sensors between us since Aug 2018!

Could it have been wiring faults all along? Or damage to the ECU plug pins / sockets (as the brake fluid was in the sockets - though I din't know - when I bought it 2 years ago)? In which case replacing the sensors has been an elusive butteryfly all along

In the meantime I will still check the wiring codes carefully and look for damage ... thanks.

Ciao, Capt K

[Incidentally Algorithm = Model = Artificial Intelligence - they are all (by mathematical definition) suspect ... as they say "All models are wrong but some are useful!"]

[captainkephart]

Hi Wheeler,
Sorry to bother you again. I've been looking at the ECU wiring diagram you posted.
To test the O2 sensor wirling I'll be disconnecting the battery and removing the three big ECU plugs.

But to test the O2 sensor circuits properly I need to isolate them completely. I see that the sensors share wire 1351 in common with device 1215. Also 1351 goes to Unit PFS1 where it is connected internally to two other wires. So I have to unplug those as well. What are they?

Do you have a decode of the devices on the diagram you could share (for future reference) please? Thanks.

Ciao, Captain K

[wheeler]

1351 is the power supply to the heater elements in the sensors, it is also a shared power supply for other sensors/actuators. 1215 is the charcoal canister electrovalve.You would check these wires by confirming power supply. The other wires that go to the ECU are the ones you need to need to isolate to test.
On the sites wiki page there is a component code list somewhere. Im sure someone can provide the link.

[GiveMeABreak]

Have a look on our Wiki - I've posted most of the more common codes there as there are far too many to list every time:

https://frenchcarforum.co.uk/wiki/Elect ... ring_Codes

[captainkephart]

Superb, thanks!
Doh ... have never looked at the wiki ... !

[GiveMeABreak]

We did start to put some stuff there, but it is really fiddly to do and time consuming, so I tend to just keep things here now - but the diagram info was already there.

[captainkephart]

Hi Marc and Wheeler,
Well, it's fixed itself - how does that happen?
I haven't opened the bonnet or done anything to it the last few days ...
I've been going to my workshop (I'm a boat builder), 15 min journey each way. Fault light has come on every time.

Today the same, arrive, park up for 4 hours. Back in the car, fault light is off ... er?
Back home, put OBD on, faults have cleared ...
Temperature gauge is now showing usual 2 bars (fault light only comes on when 3 bars are showing), always 2 bars normally even on long motorway journeys.

What does it mean? Haha, yes it means there is no Engine Fault ...
How can it mend itself and self-clear the faults? I assume it means that the O2 Sensors ARE connected the correct way round? Or ...

Oh wise Gurus of the Citroen Tribe - what do you suggest?
Is the car bewitched? Should I drive it to Brittany and through the Carnac Stones, then to Broceliande and ask Merlin?
Sorry, getting all too much ... after 2 years of this !
[Long string of smileys not included]

Ciao, Captain K

[wheeler]

Maybe remade a bad connection when you have been doing checks??

[captainkephart]

Hi Wheeler,
I haven't done any checks yet ... since you and Marc made all your suggestions, not had time ...

[myglaren]

May not have been mentioned but some faults, on replacing faulty parts, need up to five separate starts and journeys before the fault is cleared.
Then the fault disappears, as yours did.

[captainkephart]

Hi myglaren,
Ahhhhh, I see, I didn't know that - it explains a lot!

Means that at times in the past I have been trying to 'fix' a fault that is already fixed!
Aaaahh, indeed (not arrrggghh!). Serves me right for being too finicky. A lesson for others too?
Maybe a Doh! is called for ...

Ciao, Captain K

[captainkephart]

Hi Wheeler / Marc / myglaren,
Just to close the loop, I'm going to leave the car as it is and am not going to check the wiring, as discussed above, yet.
Thanks very much - I now have all the information I need when / if I need to test the connections.

For now, Fault Light is off, performance and fuel consumption are great, so not broke, don't fix it ...
There's an intermittent contact somewhere, I'm sure Wheeler is right, but I'm going to wait for a bit and see if it reappears ...

Thanks again, Captain K

[captainkephart]

Hi Team,
I'm putting the update here as this car has 'form' on this post!

Right ... new twist. Car has been fine since late Aug. Then noticed the odd slight single misfire ... no pattern.
Today, the full fault fireworks - Fault Light itself flashing (never seen before, means what?), plus message plus beeping.
Heavy misfiring on one cylinder, then after a few miles on two ... (luckily only a few miles from home) ... more flashing and beeping.

When home, engine off, wait 10 mins. Engine on, still misfiring like a tractor (sorry tractor fans). But Fault Light is now off!
Try to read the Live Data grid, get 'NO DATA' from top to bottom ... wots that mean?

Pending Diagnostic Trouble Codes (DTC) (Mode 07)
P1336 - Crank/Cam sensor range/performance. Or ME7.4.5. Combustion misfiring on unspecified cylinders.
P1340 - Camshaft position sensor B circuit Malfunction
P1339 - No Description (Manufacturer Controlled Code (Non-Uniform DTC))
Vehicle Area: Powertrain (P)

Have cleared the faults, restarted the engine and P1340 - Camshaft position sensor B circuit Malfunction has returned.
However, the Live Data can now be read (see below).

QUESTION. Is this simply a new fault completely, or another 'fault' caused by the intermittent contact on the brown ECU plug?

What do you think? Thanks, Captain K

Description Value Units Min Average Max
03 - Fuel System Status
Fuel System 1 open loop driving - 4.00 6.00 8.00
Fuel System 2 Not Reported - 0.00 0.00 0.00
04 - Calculated Load Value 34 % 34.12 39.92 44.71
05 - Engine Coolant Temperature 172 °F 165.20 168.80 172.40
06 - Short Term Fuel Trim - Bank 1 0.0 % 0.00 0.00 0.00
07 - Long Term Fuel Trim - Bank 1 -0.8 % -0.78 -0.78 -0.78
0B - Intake Manifold Absolute Pressure 12.7 psi 12.70 14.29 15.36
0C - Engine RPM 772 rpm 755.25 780.65 812.75
0D - Vehicle Speed 0 mph 0.00 0.00 0.00
0E - Ignition Timing Advance for #1 Cylinder 5 ° -7.00 -1.90 5.00
0F - Intake Air Temperature 123.80 °F 123.80 123.80 123.80
11 - Absolute Throttle Position 20.0 % 20.00 20.47 20.79
14 - Bank 1 - Sensor 1
Oxygen Sensor Output Voltage 0.145 V 0.14 0.22 0.31
Short Term Fuel Trim 0.0 % 0.00 0.00 0.00
15 - Bank 1 - Sensor 2
Oxygen Sensor Output Voltage 0.455 V 0.46 0.46 0.46
Short Term Fuel Trim 99.2 % 99.21 99.21 99.21
21 - Distance Travelled While MIL is Activated 0 miles 0.00 0.00 0.00
47 - Absolute Throttle Position B 20.0 % 20.00 20.52 20.78

[captainkephart]

Haha, this is the DOHC 1.6 petrol ...
It doesn't seem to have a camshaft sensor!

This car is on LSD?

Ah, have decoded now, not cam sensor:
P1336 - Combustion misfiring on unspecified cylinders.
P1339 - misfiring on cylinder 3;
P1340 - misfiring on cylinder 4.

Injector fault? Hopeless ...

[captainkephart]

Hi All,

The new Sagem coil pack I put in last autumn seems to have failed.
Change coil pack, now not misfiring. Result!

Ciao, Captain K

PS: I checked the spark plugs and gaps, 0.9mm not 1mm (is it that sensitive?).
Also plug colours just right, so not head gasket leak.