Question on VR6 knock sensor

[fendervg 29]

Have been getting an intermittent knock sensor error in VCDS recently - also sometimes what seems to happen is that when driving there is a very slight hesitation when initially pressing the throttle pedal, almost as if everything is slowing downs for a second, and then back to normal.

 

Would this be a symptom of a faulty knock sensor? I guess the ones that are on there have been on since the car left the factory, so probably a good time for replacement anyway.

 

Would this be the correct part:

https://www.vwheritage.com/021905377-knock-sensor-for-vr6-vw-spare

https://www.volkswagen-classic-parts.de/en/sensor-fur-den-corrado.html

 

Any reading I've done seems to suggest that the rear one is handy enough to replace, but that the front is a complete pain - any tips?

 

Cheers.

[vw rule 19]

Hello there,

 

this is from the Bentley manual for 2.8 VR6 with eng code AAA, but must be the same for ABV eng code i.e for the 2.9 VR6.

 

Knock sensor 1 (G61) Fitted on back of engine = exhaust side

(error code 00524)

Faulty sensor malfunction = knocking not recognised by ECU

Or wiring fault resulting in no signal from knock sensor 1

 

Knock sensor 2 (G66) Fitted on front of engine = inlet side

(error code 00540)

Faulty sensor malfunction = knocking not recognised by ECU

Or wiring fault resulting in no signal from knock sensor 2

 

Yeah I believe when they fail you might get a very slight misfire or rough running, the engine might feel like it's down on power very slightly.

 

The knock sensors detect pinking from the cylinders, and will tell the ECU to retard it's programmed timing range, if they pick that sound up.

Looks like the wiring attached to the knock sensor has to be fixed in place, where it runs up or across the engine block, otherwise that can cause false readings from the sensor.

Plus if the outer shielding is cracked or loose, again this can cause issues.

Also check the connector plugs for any damage or wear on or around the contacts.

 

Also it's highly important to torque the retaining bolt up to the correct torque setting, otherwise that can cause the knock sensor to not work at all, or it'll receive false readings.

 

The correct torque setting for both knock sensors on the VR6 is:

20Nm or = 15 ft Ib

 

The Bentley manual says there's no proper way to test the knock sensors,

only really if the diagnostic scanner brings up the fault codes.

 

Testing knock sensors with multimeter set at ohms. (with ignition switched off)

With the connector plug disconnected you should have infinite ohms, meaning no continuity i.e no power active.

Bentley manual says the knock sensors both have 3 pin connector plugs,

I think the average reading you should see is something between 2000 - 3000 ohms.

 

Also says you can check the wiring through to ECU to check for continuity, with plug disconnected bridge terminal pins 1 & 3 of (knock sensor 1) you should see 1.5 ohms max.

Connector plug should be near rear engine mount. (Possibly white plug)

 

Then for (knock sensor 2) bridge terminal pins 2 & 3 you should see 1.5 ohms max also.

Connector plug should be next to starter motor (plug is black)

 

Then with ignition switched on you can check for power i.e voltage, I think you should have 5 to 8 volts roughly.

 

If the ohms test doesn't work then possibly with the connector plugs disconnected, (ignition switched off) you can set your multimeter at volts, and gently tap on engine block near to the knock sensor, and see if the voltage increases or not,

but this may vary as I think knock sensors pick up different sound frequencies, from engine to engine so to speak.

 

 

Hope this helps

 

Si

Edited August 30, 2018 by vw rule

[a_riot 0]

Good info above, and I'd be surprised if the problem was the sensor itself, since its just a piezo pickup. More likely a connection issue. I saw the one on the front of my VR6 when I had the oil cooler and oil filter housing off. It'd be difficult to replace without some disassembly, so hopefully they are fine. The knock sensors don't really have any effect on the engine unless they sense a ping in the combustion chamber, so even unplugging them shouldn't cause a change in running, outside of the error code, I wouldn't think. I'll see if I can disconnect mine if it makes any difference to the engine smoothness. But without any engine knock, they don't sense anything, and thus won't sent a signal to the ECU.

[fla 9]

they might just need re-torquing, which is actually very critical.

[fendervg 29]

Ok - thanks for the very good detailed info. I'll check all the wiring and connections first and will see how I get on.

[Dox 22]

they might just need re-torquing, which is actually very critical.

 

Wire brush the block before you re-torque the sensor.

 

It can also be a fuel or timing issue, it wouldn't hurt to clean both cam and crank sensors and check there connections for corrosion