Instrument cluster temperature reading
 

Dear All,

for some time the instrument cluster temperature digital gauge on my CDTi Connie SE has been reading really high. It does give different readings, but they are insane.

So the thrust of my question is, does the outside digital temperature sensor and readout play any part in the cabin heating?

I know the sunload sensor does, so I thought the outside temp might well be taken into account.

The outside temp was around 6-7c the other day, but the car records this as 93-94!

EDIT. Just in case this helps anyone in the future - Artic and Simon (SD) were spot on when they confirmed that the exterior temperature sensor is involved in the interior heating control. After my knee op had settled down, I waggled the wiring and the sensor basically sorted itself out.

So now it reads believable outside temps and the interior heating can be set on a realistic figure - no need to set it past 80 degrees to feel a glimmer of warmth.

And as an aside, I also fitted the inline stat mod from DRMGS and that has also improved matters as expected. The old stat must have been working - ish, but decided enough was enough and the engine was just not getting up to the line like it used to.

Many thanks to all who helped me out with this. I now have another weirder issue to ask about, but that is for a separate post!

Best wishes, Frank B




This has been going on for some time, and I ignored it. However, I fitted one of the excellent DMGRS inline thermostats when the weather started to get a bit chillier, and the engine temp gauge showed the old stat was past its best.

So I expected the heating to be a bit better too, but unless I crank up the inside temp demand to say 78f, the heating is lukewarm, even though the engine temp gauge shows a reliable normal temp.

Does anyone know if fixing the outside temp sensor would help with the cabin heating - and if so, is it likely the wiring or connectors is the cause.

A further hint here is this started some time after I parked too close to a kerb in front, and the readings have been ok, then daft.

I would have crawled under the car before to have a look, but have been given a new knee a short time ago, which makes crawling around a bit of a pain - literally! Best, Frank B

Yes it does Frank.
It sounds as if you have damaged the sensor. Get a replacement fitted and you should be fine. :}

Simon

Not connected
 

the internal cabin temperature sensors are used to control the heater, the external one is just for the digital readout. I suspect that the external one has been disconnected and probably just wants the connection reinstated.

Thanks for the reply. It makes sense that if the sensor thinks it is 90+ outside, it would factor that in with the sunload sensor input.

I am hopeful I just screwed the cable/connector when I hit the kerb, but if not, as you say, a replacement is needed - or fur coats! Best, Frank B

Thanks for the reply. That is what I had hoped for, but as I know the sunload sensor is used as part of the control electronics for the climate control type of heating, I expected it to take note of the outside temperature.

However, the answer either way is fix the sensor and see what happens!

I hope it is simple, as my crawling is pretty limited at the moment, and not just by the weather.

I suppose the moral of the story is not o park like the connie is a bulldozer! Best, Frank B

The external (ambient) temperature sensor is mounted on a push in clip behind the lower grill on the bumper panel. You have to drop the front edge of the undertray to get at it without removing the complete bumper.


The external temperture display will show -30 when the sensor wiring is disconnected. When reconnected, a functioning sensor can take an hour to a full day to equilibrate back to true ambient reading.

TC

Spot on
 

Dear TC, thanks for the info. It gives me a pretty small area to search for a gubbins on a clip. Not a clue what it looks like, but it will have wires and a connector, so that should narrow it down a lot.

Interesting to hear that if the connection is not there the readout will show -30. As mine appears to think it is somewhere near Barbados, my hope it might be a cable/connector problem does look like an exercise in straw grasping.

I might try to get my wife to have a look before trying to get under the car myself though.

She can always find anything I do not want her to (no love, I bought these parts for my motorcycle years ago, before fleabay existed) so there is a chance she will respond to "if I cannot find the sensor, I will have to go on fleabay and buy one" More straw grasping. Best, Frank B

On the driver's side just behind the lower corner of the front number plate, you should see the circular front of the sensor pointing forwards. It may be possible that it has become dislodged and is pointing/touching/near to a warmer area of the engine bay, eg the radiator?

As far as heating goes, the temperature of the engine coolant will have a bearing on this, along with the time it has been running. I do not switch my heating on until the engine coolant temp shows at least 80 degrees (centigrade), as any earlier, it will take an age for the engine to reach its optimum temp. The gauge is just a guide, the '9 O'clock' position can be anywhere between 75 and 105 degrees, with 88 being regarded as the optimum.

If you have the heating on as soon as it reaches the 9 o'clock position (or before), the engine temp will drop drastically, sometimes in my tests on my car, to as little as 69 degrees (traffic was slow moving), although mine normally drops to 72 degrees, before very very slowly climbing back up again providing driving conditions allow me to open it up a little. I have seen it only reach 85 degrees after switching the heating on at 75 after a further 6 miles! The thermostat I have in mine cycles the coolant between 86 and 89 degrees depending on load.

With this in mind, the heating may only reach a lukewarm temp. Another factor to consider is the overall distance and speeds when using the heater. My first 5 miles are spent without heat, and only then will I consider putting the heating on.

There are simply too many variables for the heating to be suspected of having an issue. But monitor it by using T-Cuts breakdown of the on board diagnostic (option 7 HERE). The first test would be to make sure it reached between 82 and 88 degrees within 5-10 miles, with the heating off (speeds and engine loads will be a factor in this).

Correction
 

Sorry Lee, this is incorrect. The external temperature sensor signal is received by the instrument pack then passed on to the heating, ventilation and air conditioning ECU via the BCU on the K-bus.
(See table K-bus outputs, page 60, Body Electrics Workbook)

Incidentally it is also passed to the ECM on the CAN bus so definitely not "just for the digital readout"! :D

Simon

This running cold thing is the reason I wired in an override switch on my FBH. if it feels cold to me, (usually about 10c and under) I turn on the FBH. Not just to get the heater working, I just don't like driving for miles with a cold engine. As we know, most wear accurs when an engine is not at its correct running temp.