Skoda Octavia - Octavia engine management light staying on

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Tue 27 Oct 2015 20:42
Skoda Octavia - Octavia engine management light staying on - beanstalker

My nephew has a 2003 Skoda Octavia 1.6 petrol which has done 67000 miles. He likes the car very much and has had very few problems since he bought it in December 2014. However in the last few days the engine management light has come on and has stayed on. The car continues to run very well despite this, no loss of power or any increase in fuel consumption. His mechanic has checked it out and says it is a faulty sensor and is not going to cause problems. He did replace a sensor for the radiator fan and the light went out but came on again a short while later and has stayed on since My nephew trusts the garage a lot as he has used them for years and they do all his servicing and MOTS. They have all the latest computer aids apparently. I was wondering whether forum contributors agree with the diagnosis and whether it will give him problems if he does nothing?

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Tue 27 Oct 2015 21:57
Skoda Octavia - Octavia engine management light staying on - brum

Needs a diagnostic scan, vcds or otherwise. That will tell you whats putting the light on.

Things you can check are Brake lights not working due to faulty brake light switch.

Otherwise could be a faulty egr valve/related sensor, faulty lambda probe, intermittent misfire (from plugs/coils/leads/injectors/worn valve seats) plus other possibilities.

Engine management light is not an mot failure, but emissions may be affected, which may not pass.

If your car is pre canbus era, then cheap scanners can be got on fleabay.

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Wed 28 Oct 2015 11:25
Skoda Octavia - Octavia engine management light staying on - Railroad.

You need a diagnostic scan, but you need not pay the earth for it. Below is a link to a map of VCDS owners. Find one near you and ask for help. Most will be delighted to help you. You'll also find me on the list.

www.google.com/maps/d/viewer?mid=zQlwUpVpfeKA.kRFf...0

If your engine management lamp is on you will have one or more fault codes stored. These will give an indication of where the fault lies, but you should be aware that fault codes essentially fall into two categories.

1. Circuit faults - Where a component or wiring is either open or shorted to ground. The ECM will be able to determine what circuit is at fault, but it will not know exactly WHERE the fault lies.

2. Mechanical faults having an effect - This is where the ECM receives an inplausible signal from a sensor or a component, but where no fault in the circuit is detected. This is NOT necessarily a fault with the component itself. The ECM cannot tell if there is a mechanical fault, such as a vacuum leak. It will only know that the information received from the MAP sensor or O2 sensor isn't what it should be. In such cases many technicians will automatically blame the sensor, and they are very often wrong. For example, a partially blocked fuel injector will upset the reading from the O2 sensor, and the ECM may generate an O2 sensor fault code. In this case the O2 sensor is not the fault, and in any case the ECM has no way to directly detect a blocked injector. I hope I'm making sense.

The reason why the MIL went out for a couple of days is due to the way your car's European On Board Diagnostic (EOBD) system works. When you switch on the ignition the system carries out a self check. The EOBD system has readiness monitors which monitor components, misfires, EGR and O2. Under normal conditions these readiness monitors are set to 'Ready'. This means the ECM is monitoring the system and everything is working. When you clear fault codes the readiness monitors are set to 'Not Ready'. Before they become 'Ready' again the car will have to go through a drive cycle during which time the system is not being monitored. It will take a couple of days before the system is 'Ready' again and monitoring begins. This is why your fault codes reappear after a couple of days. That's also a good clue that your fault in particular falls into the second category, because if you had a circuit fault the code would reappear straight away.

A cheap scantool may serve a purpose, but VCDS is much more comprehensive. You need to do some live data checks for manifold vacuum and fuel trim to get to the bottom of your problem. Just changing sensors for the sake of it is little more than pure guesswork.

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Wed 28 Oct 2015 15:01
Skoda Octavia - Octavia engine management light staying on - 659FBE

Good advice above - also bear in mind that if the EML has been on, a fault code will be stored and VCDS will find it. Your garage may be using generic equipment. The fan switch is an unlikely candidate.

However, I note the year of the vehicle. Up to and slightly beyond build year '05, dear old VAG used engine coolant temperature senders with a design defect. They were potted internally in hard white epoxy resin, which fractures the brittle NTC elements when thermally cycled. The faulty units have a black body and part number 078919501C.

Replacement units have a green body and revised part number 059919501A, and have a soft potting material. These are readily and cheaply available from GSF and the like - avoid Chinese versions on eBay.

Although I do not normally countenance "random" parts swapping, if your temperature sender has a black body, I would change it (and the "O" ring seal) anyway - it's a cheap and quick job. The EML will go out after a couple of start cycles if this proves to be the cause.

659.

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Fri 30 Oct 2015 08:38
Skoda Octavia - Octavia engine management light staying on - Railroad.
I would agree with changing the coolant temperature sensor as mentioned above, because the black ones were known to go faulty and replaced with the green ones. Whether or not a faulty CTS would generate a fault code though is another matter. It only would if the sensor were to become open or short circuit. If it was reading incorrectly but within limits then no fault code would be generated because the ECM would know no different.
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Fri 30 Oct 2015 09:42
Skoda Octavia - Octavia engine management light staying on - 659FBE

The problem with the black-bodied temperature sender is that the hard epoxy filling has a relatively high coefficient of linear expansion. The assembly which includes 2 thermistor beads, is constrained within a brass tube.

Thermistors are extremely brittle, the elements being made from sintered metallic oxides. The stresses caused by thermal cycling (what better place than on an engine?) causes the beads to fracture.

In my experience, these senders do not read incorrectly, they fracture and become intermittently open circuit - which puts on the EML.

Designing engine mounted components to withstand thermal cycling used to be one of my areas of work - I've sectioned hundreds of failed devices. I am astonished at how many thermal cycling failures still occur (solder fatigue of small relay pins on printed circuits, for example) and how some makers, especially VAG appear to have, in my view, little real understanding of this mode of failure.

659.

Edited by 659FBE on 30/10/2015 at 09:45

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Fri 30 Oct 2015 11:06
Skoda Octavia - Octavia engine management light staying on - Railroad.
I had one fail on an Octavia I used to own. We were on holiday at the time in Cornwall when I noticed driving along the A30 the temperature gauge was reading close to cold. Immediately I put on the heater and established that the engine was not overheating and that it had not lost any coolant, although the engine did appear to be running slightly differently. I pulled into a service area to look under the bonnet and waited for 30 minutes, and when I returned to the car the temp gauge was working normally again and the engine was running fine. I changed the sensor for the green type and never had that problem again. The ECM was responding to the faulty sensor and was fooled into thinking the engine was cooler than it actually was, hence the poorer running. No fault code was generated though.
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Fri 30 Oct 2015 12:34
Skoda Octavia - Octavia engine management light staying on - craig-pd130

I don't know if the 2003 Octavia petrols were still using the motorised throttle body set-up, but if they were, the coolant temp sensor failing causes the idle rpm to go all over the place when the engine is warm. The ECU thinks the coolant temp has gone from 90 celsius to minus 10 in an instant, and correspondingly richens the mixture for cold running.

If the idle speed is all over the place when the engine is warm, it's a sure sign the coolant temp sensor is dying.

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Fri 30 Oct 2015 22:22
Skoda Octavia - Octavia engine management light staying on - Big John

You need it scanning to find out what code is stored.

As the car works OK with no real increase in fuel consumption I don't thinks it will be temperature sendor (fuel consuption increases with this as it always thinks it is still warming up). My gut feel is this is something to do with the EGR valve - you may get something like EGR insufficient flow - this can take a few days to show up after it has been cleared which is what you experienced.

On my 2001 Octavia 1.4 16v my EGR failed closed some years ago but as it has done a highish mileage ive not bothered getting it fixed for various reasons:-

1) It doesn't affect the running of the engine (still 40+ mpg)

2) With a high mileage engine because the EGR never opens it never coats the pipes and throlttle body with the c£$%p that comes down the exhaust (even though I don't need to top up it's probably burning a bit of oil now)

3) You don't fail the MOT for an illuminated EML

4) Oh - I also don't fancy undoing some VERY rusty looking nuts and threads attaching the EGR to the exhaust!

If it fails open it would affect the engines tickover and running

Edited by Big John on 30/10/2015 at 22:24

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Sat 31 Oct 2015 00:21
Skoda Octavia - Octavia engine management light staying on - A3 A4

Another for the temperature sensor here.

I had the same problem on my OHs 2003 Audi 1.6 A3 (same engine?)

Replacing the temp sensor sorted it, Iight out all good. £7 off EBay.

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