Exhaust Gas Temperature Sensor - Any suggestions appreciated

[Deep Blue]

2009 VW Passat CC 2.0TDI (CBBB engine)

Had three codes come up on the scanner: 01348, 09326 and 09327 - all refer to Exhaust Gas Temperature Sensor (Circuit Bank 1 Sensor 4 it appears).

Glowplug flashing amber warning light comes up and then the amber check engine light. Codes can be cleared but come back fairly soon.

When this happened some time ago, I took it to a VW mechanic and I noticed they were working under the windscreen - removing built-up carbon from the looks of it and said I'd probably have to get it done again in a few years.

With this engine, the EGR and ASV are right at the mid-front of the engine, so I'm not really sure what the mechanic was cleaning out last time (couldn't have been the DPF?).

Anyway, I decided, as a first step to buy Liqui Moly "Diesel Engine Intake Decarb", to see if the issue is being caused by carbon build-up.

I have used a DPF cleaner solution fairly regularly (added to fuel tank) and gone on long trips in Sport mode to try and keep things in check. I have also used a diesel fuel additive to keep the fuel system clean. Additionally, I do regular oil changes with a good quality (DPF compatible) engine oil.

Any opinions on the Liqui Moly Decarb?

Is the issue likely to be a clogged Temperature Sensor?

Is this sensor easy to access/remove and replace (not too expensive)?

Any other thoughts or experiences with this?

[Lucas_R]

Its quite likely that you have a faulty exhaust temperature sensor and it will need to be replaced. It might sound unimportant, but without this sensor working, other things (DPF FILTER = EXPENSIVE) will be affected and it will cost you a lot more + car off the road.

Some info here on that sensor: Exhaust Gas Temperature Sensor - 01348

The Liqui Moly decarb works ok but its quite weak, ive used it a few times and have a can of it in my garage right now that ill use again in the next few weeks. But I have found the Nulon Throttle Body and Carby cleaner to be far more effective to remove the sooty carbon buildup, but you dont want the carby cleaner being sucked into the engine, so you need to be careful with it.

[Deep Blue]

Okay Lucas_R - thanks for that! Will have to research the new sensor - remove and install. I assume the exhaust gas sensor #4 is under the middle of the windscreen somewhere (are there actually four of them?) near the dpf. Is there a schematic of this engine (2.0 TDI CBBB) somewhere - I can't exactly work out the flow of air from MAF through to the turbo, then intercooler, then ASV, then EGR, then intake manifold then outlet manifold, then DPF, then turbo I assume (Temp sensors around here?), then exhaust; whilst exhaust recirc goes through EGR cooler, then to EGR valve? With the engine being transverse it confuses me a little at first sight, and of course it's cramped up, especially at the back!

Might have to finally get a partial sub to ERWIN?

I presume the mechanic last time around might have been unblocking the EGR cooler?

[Deep Blue]

So you would use the Nulon product to clean the ASV (throttle body) and EGR valves when they're removed from the vehicle? What about the EGR cooler - doesn't that block as well with carbon/soot?

The Liqui Moly doesn't require removal of any parts apart from the air hose connecting to the ASV, but as you said, it's not terribly effective. If I use it then it will be just before I do an oil change as I suspect it will contaminate the oil.

I guess that's all academic though as I need to replace the temperature sensor first!

[Lucas_R]

So you would use the Nulon product to clean the ASV (throttle body) and EGR valves when they're removed from the vehicle? What about the EGR cooler - doesn't that block as well with carbon/soot?

The Liqui Moly doesn't require removal of any parts apart from the air hose connecting to the ASV, but as you said, it's not terribly effective. If I use it then it will be just before I do an oil change as I suspect it will contaminate the oil.

I guess that's all academic though as I need to replace the temperature sensor first!

Yes 1st point is to replace the faulty sensor.

I have used the Carby Cleaner product on a friends car (Holden Colorado) about 4 months ago without removing anything and it didn't harm anything. I used it to clean the throttle blade, MAP sensor and about a 1.5 cans of it straight down the inlet manifold. It fixed that car and got it running well again - until next time.

On my own personal car I have only used the Carby Cleaner on parts that I have physically removed for cleaning - but given the success with my friends car I might give it a try and see if my car is happy with having carby cleaner sprayed down its throat or not.

I have used the Liqui Moly product about 4 or 5 times now and spray that down through the throttle blade while the engine is running. I always do it the same day that I am doing an oil change. I have used a borescope camera before and after and just found that it doesn't do much. I tested multiple products (petrol, degreaser, Liqui Moly and carby cleaner) and found the carby cleaner to be the most effective at dissolving the carbon buildup.

[Deep Blue]

Okay, might have to get this attended to by a VW mechanic - replace exhaust gas temperature sensor 4. It looks like this sensor is in a very hard-to-access spot between the back of the engine and the firewall and also requires a special tool and access from underneath as well - too much faffing about. I understand it initiates a DPF regen, so I'll get the car booked in asap lest the DPF ends up blocked! Guess I might be looking at c.$600 to get this done?

Interesting though, the Foxwell can independently initiate a DPF regen whilst the car is running - would this mean you wouldn't have to rely on this sensor?

[Deep Blue]

One other thing that's strange, the EGT sensor faults only came up very soon (following day) after I added Penrite Convoy DPF Cleaner to my fuel tank! Could this be causing the problem (too high an exhaust temp) or just a coincidence?

[MIG]

The sensor can read up to 900C; I don't think the cleaner would have killed it.

03L 906 088 HM part number for the sensor.

The assembly overview shows the exhaust manifold may need to be removed for access; sensor 4 is just after the DPF; I would say it might be accessible on a lift from the underside.

The "special tools vw 3337" is just a standard lambda \ o2 sensor socket.

[Deep Blue]

Thanks for all your great advice MIG!

[Lucas_R]

Interesting though, the Foxwell can independently initiate a DPF regen whilst the car is running - would this mean you wouldn't have to rely on this sensor?

My understanding is that it wont initiate a DPF regen unless all related components are working without fault - at least it wont on my car. I have a Carista OBD tool and it has the same "initiate DPF regen" function which I use regularly so that I can perform a regen at a convenient time to me, even if the filter is only 90% full for example.

Ive never had an issue using the Penrite DPF cleaner (the stuff you put in the fuel tank) I use one whenever we go on a road trip to give it a good cleanout.