Possible incipient failure warning?

Skoda Octavia Elegance TDI 2 litre year 2008 mileage about 90,000.

Normal behaviour: ignition on, display in centre of dash flashes the top part (mpg figures etc) for a few seconds. If radio is on, centre console display shows outside temperature (today 13.5 degrees).

The lower part of the display flashes a spanner symbol.

If I wait many seconds, the lower part of the display shows the trip miles.

Whatever, I start the engine and drive off.

Yesterday and today, after 2 miles there is a "ding" sound. (The same ding as the indicator warning when parked.) The top part of the display in centre of dash flashes for a few seconds then shows the expected information, and the centre console shows a ridiculous outside temperature like minus 2.5 degrees.

Over the next ten minutes the outside temperature drifts up to what I expect it to show.

Two days ago I did drive through some serious puddles - floods several inches deep - so perhaps water has got somewehre it should not?

Is this an indication of a more serious failure about to happen?

Reply to
Graham J
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the ding is probably a warning of ice (it thinks it is minus 2.5) I think your diagnosis of water in something is very likely. All you can do is wait and see, or you could try disconnecting any connectors you can find and blasting them with wd40.

Reply to
Mrcheerful

It's telling you it wants a service. Or, if it's had a service recently, it wants the service interval count-down resetting.

Agreed. I'd be starting with the outside temp sensor - if it isn't in the underside of a door mirror housing, then it'll be behind the front bumper. Just disconnect it initially - it'll read either absolute minimum (-40 or so) or absolute maximum (50 or so), depending on which way the thermistor used goes.

Reply to
Adrian

Underside of the left door mirror is quite likely given the puddles the other day!

Reply to
Graham J
[snip]

OK, before I go out and get grubby looking for the sensor, can anybody tell me exactly where it is, please?

The vehicle is a Skoda Octavia Elegance TDI 2 litre year 2008.

TIA

Reply to
Graham J

OP here.

The local independent garage was able to replace the sensor for me - evidently they are known to fail like this.

However the intermittent problem is still there.

They showed me how to gain access to it. Part of the plastic grill in the front bumper can be removed - it's about 4 inches by 5 inches. It's simply held in place by plastic barbs and with a good straight pull it comes off.

This reveals some of the body metalwork. The sensor clips into a hole about half an inch diameter and is held in place by a metal bracket fixed behind the metalwork using a torx screw. The area beside this is open and I can see the cable running to the sensor - it's protected by a sort of plastic corrugated tube.

Evidently the bracket was badly bent, and the hole through which the retaining screw held it was damaged as if the screw had been punched out. The garage people re-fitted it with a penny washer to spread the load around the damaged hole.

The hole through which the sensor mounts had also been damaged and needed to be opened out with a drill to accommodate the new sensor.

It's not clear how this could have happened, but on the plastic adjacent to the removeable part of the grille there are couple of tiny chips in the plastic finish. We speculated that the car had perhaps been driven into a bollard or similar with a protrusion at just the right height to damage the sensor mounting; and that the repair had been achieved by buying a replacement plastic piece for the grille. I've only had the car 6 months so I've no idea of its history.

So it should be easy for me to investigate further.

Can anybody tell me the exact nature of the sensor, please? Is it simply a temperature sensitive resistor, or something more complex?

Does anybody have a drawing which would indicate how the cables run from the sensor to the control unit, so I can check for damage along their length?

TIA

Reply to
Graham J
[...]

IDK, but would be surprised if it's not just a thermistor. Do you have the old one? If so, it would be easy to check with a multi-meter if the resistance changes with temperature.

There is no information about this sensor on Autodata. (Not unexpected; it's primarily to help with 'running' faults.) I doubt that anyone would have access to loom location diagrams, even dealers.

Common wisdom (read as 'Uncle Google) suggests the connector for the sensor is the usual cause. Unfortunately it is part of the loom, and is unavailable separately.

Chris

Reply to
Chris Whelan

Out of interest, do the manufacturers have diagrams? Given what I've read on this newsgroup in the past I somehow doubt it! Perhaps manufacturing simply copies a hand-made prototype?

Thanks.

Given the possibility of having suffered mechanical damage I'm sure you're right - the connector will need sympathetic attention.

Is it likely that one side goes to ground, so one cable in the loom will go to a grounding point nearby?

Reply to
Graham J
[...]

For sure. Very detailed ones, that will never see the outside of the factory.

Of course, it was was a Peugeot I'd doubt it even had a wiring diagram...

I wouldn't have thought so, if it has two wires. For simplicity it would ground locally otherwise.

Chris

Reply to
Chris Whelan

Graham J wrote: [snip]

OP here ...

Removed sensor and disconencted it.

Measuring across sensor at room temperature (18 deg) shows 945 ohms (same both directions). Put sensor in freezer for 10 minutes - now measures 2.7k ohm. (This is with a digital meter operating on a 3v supply.)

Measuring the connector on the cable loom - one contact reads 0v, the other about 5v.

*** But *** with sensor disconnected dash display shows --.- and radiator cooling fan comes on even when engine not running. So the control system must know what the highest resistance is likely to be and uses an open circuit (probably 100Mohms) to infer that the sensor is not present.

As an aside, when the sensor has read a temperature much lower than what I know the ambient to be (say -12 deg) it seems to me that the cabin heating works harder - despite the cabin thermostat setting.

Anyway, I cleaned the spring contacts in the connector and bent them to increase the contact pressure - so we will see what happens.

Google found these:

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Reply to
Graham J

back track the wires to the ecu and see if the sensor readings are registering the same as they do at the sensor.

Reply to
Mrcheerful

^^^this.

Reply to
Chris Bartram

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