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Afternoon all. There always seems to be things to keep us busy. VCDS threw this code today For knock sensor 3. Cleared the code and drove it to work. Went so much quicker. Went to accelerate again and it almost coughed and the tone of the engine changed and it felt restricted again. Which I presume was the fault reappearing. Will confirm later by checking the code again.

Just wondered how much hassle is involved with knock sensor 3 and it’s location etc. Or is there something else that may cause the code

Unfortunately I’ve no knowledge on the subject at all but I was wondering if the EML come on each time you guys plug the VCDS in or do you just plug it in every now and then to see how the cars performing and then find these issues by chance?

Sorry for the side track.

Has to be the sensor or the wiring. Suppose it could be a duff ECU but it’s extremely unlikely.

I’d check the wiring first. Get hot in there and could make the wiring a bit fragile after lots of heat cycles.

ChrisA wrote: ↑

Thu Jun 11, 2020 6:40 pm

Unfortunately I’ve no knowledge on the subject at all but I was wondering if the EML come on each time you guys plug the VCDS in or do you just plug it in every now and then to see how the cars performing and then find these issues by chance?

Sorry for the side track.

Some faults put EML on, some don’t.

Using VCDS you can check the state of the various modules of the car. It has no effect on the faults. Unless you want it to.

Shoppinit wrote: ↑

Thu Jun 11, 2020 6:44 pm

Has to be the sensor or the wiring. Suppose it could be a duff ECU but it’s extremely unlikely.

I’d check the wiring first. Get hot in there and could make the wiring a bit fragile after lots of heat cycles.

Cheers mate. Will see if I can get in there tomorrow. Is it from the top or bottom. Any ideas how much hassle they are to change ?

I’ve got to strip the air box off to replace the spark plugs and fit new Apikol seals anyway. Just wondering if it’s worth swapping it out at the same time. Or if there is nothing obvious with the wiring

2 of them are under the inlet manifold. The other one is down under the exhaust manifold on bank 5-8.
Check the green connectors that are mounted on the top of the inlet manifold first. I had to replace 2 of these connectors.

Gregstv wrote: ↑

Thu Jun 11, 2020 8:26 pm

2 of them are under the inlet manifold. The other one is down under the exhaust manifold on bank 5-8.
Check the green connectors that are mounted on the top of the inlet manifold first. I had to replace 2 of these connectors.

Ok bud. Will do. It’s knock sensor 3 g198. So thinking this might be the odd one low down But will check the plugs tomorrow morning and report back

The connectors look ok as does what I can see of the wiring. From what I have researched this is knock sensor 3 the wire from this disappears down the front of the inlet manifold out of sight.
My readings on them are Looks like cylinders 7-8 are giving lower readings. Also 1-6 were fluctuating with the engine running. And 7-8 stationary.

Has anyone changed them or any advice for what needs removing to get to them. Looks like inlet manifold off and then accessible. But any help appreciated

Yeah, 7 and 8 are checked by knock sensor 3 (G198).

You could check the connections at the knock sensor, but you'll have to get to it first and it's under the inlet manifold.

You could also try re-torquing it. They are very sensitive to tightening to torque, but if you're going to the trouble of getting at it you might as well just put a new sensor on.

While you're in there you might as well replace the suction jet / non-return valve which has a tendency to expire causing all sorts of vacuum misery. Test the after-run coolant pump, too. If it's dead (they die discretely) you can replace that, too.

My concern before starting this removal is where the sensors actually are. Is this the best way to get to them or does the wire lead down and make this better accessed from underneath.

There's nothing fundamentally difficult, just lots of bits to remove and much faff. The throttle body can stay on, but the air combiner attached to it needs to come off, so you're going to have to put the lock carrier in service position. If you've got a timing belt due, now's a good time.

Then fuel rails, coolant hoses, vac hoses, etc.

Have you got the workshop manual?

Just done the cambelt with help from a mate as the most intricate part was beyond me

Try spraying the connectors with some contact cleaner. You never know.