EML 'on' again

[rab60bit]

KV6 developed a misfire last year which I fixed by giving the old girl a new set of plugs and coil packs but the diagnostic check also pulled up an O2 sensor problem - which I thought I'd addressed. After a while and to date I'd subsequently been suffering 'another' persistent EML warning, it extinguishes itself now and again (often but not always on a restart from cold) but inevitably reappears.
Can anyone help me out interpreting these current fault codes (which were taken today). It was the front O2 sensor that I'd changed last year but I also moved the old front sensor to the rear position (bad move changing two things but I'd tried the new sensor in the rear position first and it didn't appear to fix the EML fault) so I'm now a bit lost on what has happened. As the fault codes show the current situation I'd appreciate some informed opinions as to exactly what they are telling me right now.
Another O2 sensor might be the fix but any other thoughts gratefully considered

Not able to upload image, fault codes are:
P1472. Vis power Valve Always Open
P0151. O2 sensor 2 Front
P0140. O2 sensor 1 Rear No signal
P0174. Fuel system 2 Lean Limit

[trikey]

Chafed wire on the rear sensor?

Sent from my SM-G780G using Tapatalk

[SD1too]

Originally Posted by rab60bit

Can anyone help me out interpreting these current fault codes (which were taken today) ... I'd appreciate some informed opinions as to exactly what they are telling me right now.

P1472. Vis power Valve Always Open
P0151. O2 sensor 2 Front
P0140. O2 sensor 1 Rear No signal
P0174. Fuel system 2 Lean Limit

I'll try John!

P1472
This relates to the actuators and valves in the inlet manifold chamber. Either the power valve linkage is detached from the actuator or the actuator is not operating due to an internal electrical fault. Club member Stocktake is best placed to assist with this. It won't cause your EML to illuminate though.

P0151
RAVE says this sensor is for bank 2 which is the right-hand bank located at the rear of the engine bay: "sensor circuit low voltage, short to ground or air leakage/line break".

P0140
RAVE says this is downstream sensor 2 for bank 1 which doesn't make sense to me because there's only one sensor dedicated to each bank! As it diagnoses "no activity" this is probably a spurious fault code if you're using an aftermarket reader.

P0174
The right-hand bank (rear of engine bay) is running lean. Since P0151 reports a problem with the sensor resulting in an incorrect output signal, the engine control module deduces that the bank's mixture is lean when it either isn't or corrective action is taking place.

So you need to look at the fitment of the R.H. bank sensor and check the wiring for damage as Trikey has said.

Simon

[rab60bit]

Originally Posted by trikey

Chafed wire on the rear sensor?

Sent from my SM-G780G using Tapatalk

Are talking the actual O2 sensor to plug wiring underneath the car or on the loom from the plug back to.....where?

[rab60bit]

Originally Posted by SD1too

I'll try John!

P1472
This relates to the actuators and valves in the inlet manifold chamber. Either the power valve linkage is detached from the actuator or the actuator is not operating due to an internal electrical fault. Club member Stocktake is best placed to assist with this. It won't cause your EML to illuminate though.

P0151
RAVE says this sensor is for bank 2 which is the right-hand bank located at the rear of the engine bay: "sensor circuit low voltage, short to ground or air leakage/line break".

P0140
RAVE says this is downstream sensor 2 for bank 1 which doesn't make sense to me because there's only one sensor dedicated to each bank! As it diagnoses "no activity" this is probably a spurious fault code if you're using an aftermarket reader.

P0174
The right-hand bank (rear of engine bay) is running lean. Since P0151 reports a problem with the sensor resulting in an incorrect output signal, the engine control module deduces that the bank's mixture is lean when it either isn't or corrective action is taking place.

So you need to look at the fitment of the R.H. bank sensor and check the wiring for damage as Trikey has said.

Simon

So I've got two distinct faults
1. Something wrong with the variable inlet manifold (spoke with Stocktake some time ago about this same issue, he said the same thing about the EML but if it doesn't actuate the EML why/how is there a fault code generated?)
2. I thought the 2 O2 sensors acted as comparators and diagnosed the gas mixture pre and post cat ie dealing with all the mixed exhaust gases generated from both banks

[SD1too]

Originally Posted by rab60bit

So I've got two distinct faults

Yes.

Originally Posted by rab60bit

1. Something wrong with the variable inlet manifold (spoke with Stocktake some time ago about this same issue, he said the same thing about the EML but if it doesn't actuate the EML why/how is there a fault code generated?)

Illumination of the EML is basically triggered by faults related to exhaust emissions. The VIS system affects performance not emissions so the EML is not illuminated. Not all fault codes trigger the EML.

Originally Posted by rab60bit

2. I thought the 2 O2 sensors acted as comparators and diagnosed the gas mixture pre and post cat ie dealing with all the mixed exhaust gases generated from both banks

Your 2004 car I would expect to have three O2 sensors; one per bank pre-cat and the third post-cat. It's a very complicated subject but in very simple terms the pre-cat sensors check that the air:fuel ratio is correct and the post-cat sensor monitors the catalytic conversion. If you search the internet you'll find a fuller, more technically accurate explanation.

Don't over-think this John. It's easy to get bogged down in technical intricacies. Just examine the wiring as Trikey has suggested, starting close to the sensor as that's where the heat source is, most likely to cause a problem.

Simon

[rab60bit]

A new DMGRS O2 sensore should arrive by latest tomorrow so I'll get underneath for a good look over everything at the weekend. I think there are just two sensors, one pre and one post cat. on later cars but I'm happy to be corrected...anyone?

[SD1too]

Originally Posted by rab60bit

I think there are just two sensors, one pre and one post cat. on later cars but I'm happy to be corrected...anyone?

On the V6 there is an O2 sensor in the exhaust downpipe from each bank, both before the catalytic converters. You can see the mountings here. For V6s built during and after the year 2000 there may be a third post catalyst sensor but I'm not sure about that.

Simon