What is a TDC and what are the 'symptoms' of failure? - Renault Forums :: Independent Renault forum

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post #1 of 15 (permalink) Old 28th February 2011 Thread Starter
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What is a TDC and what are the 'symptoms' of failure?

And please be nice because it's my first time

Hubby has my old megane diesel estate (megane II?) 2004 plate. For the past few days it has been a stroppy mare in whether it will start or not.

If you unlock it and the dash lights up when the door is opened, it will start. If the dash doesn't light up, it wont... but will start if you use jump leads.

Took it today to get the battery checked, battery is tested and is fine, reconected and it then needs a jump. Spoke to an autoelectrician who suggests trying a new battery. So we do and nope it won't start, old one goes back in and it starts. Luckily we have a screaming toddler so the guy doesn't hang about wanting payment for the almost purchase of a battery we don't need.

So after searching your forums tonight, I keep finding reference to a top dead centre (sensor is it?) failure causing intermitent starting problems. But since I am no good with engines, I can't work out what it does and if it would cause our problems. Wiki failed me. Plus I have homework to do and was hoping someone else would look into it all for me

Suggestions welcome before hubby books it into the £25ph autoelectricians on Wednesday and I have to tell him that I actually spent the emergency savings on this really cute outfit for the above mentioned screaming toddler. And maybe also some shoes that are hidden under the bed...
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What is a TDC and what are the 'symptoms' of... Engines roby37 14 10645 28th February 2011 06:08 PM
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post #2 of 15 (permalink) Old 28th February 2011
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Re: What is a TDC and what are the 'symptoms' of failure?

Hello and welcome to the Renault Forums

Yes it is a sensor. a Top Dead Centre sensor signal is used by the fuel/ ignition systems on both petrol and diesel cars and measures when usually No1 piston is at top dead centre or in other words at the top of it***8217;s stroke before returning back down the bore.

The ECU then knows when to inject fuel in both diesel and petrol engines and ignite the spark plugs in the case of petrol engines.

Last edited by Recycled Scenic; 28th February 2011 at 06:26 PM.
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post #3 of 15 (permalink) Old 28th February 2011
 
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Re: What is a TDC and what are the 'symptoms' of failure?

The TDC sensor is also called a crank position sensor.

See here for a explanation of what it does. http://en.wikipedia.org/wiki/Top_dead_center

Also look at the bellow thread, it will tell you where to find the TDC sensor and how to clean / replace it. The car and engine may be different to yours but the location and prinicpal is the same.

TDC Sensor Replacement (with pictures!)

Welcome to the forum by the way.
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post #4 of 15 (permalink) Old 28th February 2011
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Re: What is a TDC and what are the 'symptoms' of failure?

I doubt it is anything to do with the TDC .

If your starter does not turn over to start the engine it's not the TDC Sensor and The TDC will not cause your dash to not light up.

From what you said it seems more likely to be battery leads or earth or some other connection.

A problem well stated is a problem half solved !
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post #5 of 15 (permalink) Old 28th February 2011
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Re: What is a TDC and what are the 'symptoms' of failure?

I go along with the above post. When it is in no start mode try connecting a jump lead between the battery negative and the engine ( to something substantial and clean) that will test the engine earthing. If still no go connect from battery(neg) to a bare metal part on the body and again try a start.
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