Knock Sensor

1993-Present: C200 CDI, C220 CDI, C270 CDI, C180, C200 Kompressor, C230 Kompressor, C220, C230, C280, C300 C350, CGI & CDI BlueEfficiency variants
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rmt6668
A Class
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Joined: Sun 04 Nov, 2007 9:45 pm
Model you own: w189

Knock Sensor

Post by rmt6668 » Tue 11 Dec, 2007 11:05 am

Hi

I like ot find out whats the function of a knock sensor? What if it fail, the symptoms? I have a part number 0031538028.

Thanks

OzC36
Dernburg Wagon
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Re: Knock Sensor

Post by OzC36 » Wed 09 Jan, 2008 12:16 am

As I understand it, the knock sensor is a microphone that detects detonation in the cylinders. If detonation is detected the knock sensor sends a signal to the ECU and appropriate measures are taken to adjust timing of the spark to stop detonation (retard spark timing).

I may be corrected by a more knowledgeable person.

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John Green
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Re: Knock Sensor

Post by John Green » Wed 09 Jan, 2008 9:20 am

Thats basically correct, it is a safe guard system, very important on cars with a cat, as you do not want unburnt fuel getting to the cat as it will damage and block it.

rny6668, what did you do with your loom problems?
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rmt6668
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Model you own: w189

Re: Knock Sensor

Post by rmt6668 » Sun 20 Jan, 2008 1:27 am

The loom is now repaired & working fine. Also had a few things done on the car. ie New set of spark Plugs (4) & new wire set. Replace 1 of the Coil Packs (the other one is 1 yr old). Also added Nulon Octane Boost & Clean into the petrol to clear the fuel injectors.

All came up very nicely also tried to run the car at high speed & over a distance to burn fuel.

But its always a struggle going uphill.

Unfortunately the car still not fix, & seems to be getting worse again. I like to buy a Diagnostic Tool which is economical but effective to try to read whatever codes. However the is no CEL whatsoever ever since there is this issue. Is it true that the ECU need to reset whatever error codes ther may be stored. I now have remove the battery in the hope it can clear some of the error.

I may even check the spark plug to see if there is any problem to be seen there?

Thanks

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John Green
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Re: Knock Sensor

Post by John Green » Sun 20 Jan, 2008 9:03 am

Did you use wire with the correct rating? Most of the sensors on this sytem work with millivolts not volts so a change in the resistance of the loom will have a big effect.

Clearing the codes should help, most workshops should do it for very little. We change $40.00 to wipe the system memory.
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rmt6668
A Class
Posts: 14
Joined: Sun 04 Nov, 2007 9:45 pm
Model you own: w189

Re: Knock Sensor

Post by rmt6668 » Sun 20 Jan, 2008 10:52 am

I bought the wires from Repco & autobarn ,atching to the right gauge & also the amps. What they say is as long as the gauge is thicker than the one being replaced is fine but must not be fine gauge.

Now you mention, thats not ok?

I want to buy a diagnostic tool for my W202(1994) but can also scan W210 (2001)? Can you recommend? I think the car now is struggling to even go to 20km/hr, may it be in limp mode?

OzC36
Dernburg Wagon
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Re: Knock Sensor

Post by OzC36 » Sun 20 Jan, 2008 2:16 pm

What John is saying is that the wiring to the (cam angle, crankshaft angle and I think also the knock sensor) sensors is very special (co-axial signal wire).

You can buy the correct repair kit wire with the connector attached from Mercedes.

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John Green
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Re: Knock Sensor

Post by John Green » Sun 20 Jan, 2008 4:45 pm

You need to fit a new loom before you do anything, the repair technique just does not work. Yes you can buy some repair section from MB for the loom, but my experiance is that if one bit is rotten than the whole thing is, so just replacing a few bits is a waste of time. This is not me trying to sell a loom, just giving you the facts. Every time you start it up with something not working the way it should you are increasing the chances of making the whole situation worse than it is now. You could fry the engine ECU, you could stuff the cat, and heaps of othe things.

This is one of the probems with later model cars, there are many people on this forum, who stuff around with old bangers and most of the time get it right. And if they don't well maybe they are late to work that day... But later model cars are a differant ball game. The other problem with late model bangers is that when you do something silly like stuff the ECU then you are up for huge money to either fix or repair it. Second hand ones don't work on most late model cars as they are hard coded to the chassis number of the car.

About 6 months ago we had a 1994 C180 Classic with about 220000kms in with a dead ECU. Cost of the new part was around $6500.00, Car was worth no more than $6000.00 as it was not the cleanest example in town. So what do you do? Well in this case we talked MB into selling it to us at a discount and wound up selling the owner a new one for aound $4500.00. If MB had not come to the party then the car would have been a right off. Compare this to the old W123 280E where you can pull an ignition module from the U Pull It and away you go.....

The scanner you ar talking about costs heaps, well a decent one that actually works does. You can get a cheap one that will spit out codes, but unless you can then decifer them it is worthless.
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