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Chat Area => General Car Chat => Topic started by: terry paget on 22 November 2020, 11:27:40

Title: P0115 Engine temp circuit malfunction
Post by: terry paget on 22 November 2020, 11:27:40
2008 Astra 1.6 petrol manual saloon

Daughter has now found the diagnostic socket on her Astra, and the above fault code has been displayed.
It first appeared last Monday, with no apparent car problems. She used the car in the week, on Friday evening it started hesitantly, cranking slowly but starting eventually, she got it home and rang me. This morning she found the socket, and got the above fault. The engine did start this morning.

Before I expected either dying battery or failed alternator, not so sure now. I am in Somerset under lockdown, she is in Enfield, 120 miles away.

Please advise.
Title: Re: P0115 Engine temp circuit malfunction
Post by: Nick W on 22 November 2020, 11:34:27
Live data.


Start the car from cold, and watch how the sensor reading changes as the engine warms up. Check if the temp gauge uses a different sensor, and compare the changes. A cheap laser thermometer will give a rough idea of what the water temperature actually is at various points around the engine and cooling system. The lead on an OBD reader should be long enough to reach out of the door, although the Astra might only be enough to put it on the dash so it's visible through the windscreen


Inspect the wiring at and around the sensor, both visually and with a meter.


A new sensor isn't expensive if the wiring checks out OK.
Title: Re: P0115 Engine temp circuit malfunction
Post by: iansoutham on 22 November 2020, 14:13:58
Change the thermostat (comes with housing).  Common problem.

To confirm, if the live data of the temperature sensors show them both rising at similar rates (one on thermostat housing, one on radiator) this will confirm diagnosis.

There was a TSB for the wiring on some aircon models rubbing through but normally just the stat assembly.
Title: Re: P0115 Engine temp circuit malfunction
Post by: terry paget on 22 November 2020, 15:48:08
Thank you gentlemen. The car is still running. I hoped on receiving the first phone call that the car would bring daughter home near Christmas, when I could repair it, but on Friday when it struggled to start I worried. From what you say it should still run until Christmas without intervention. Do you agree? Otherwise I should advise her to take it to a local garage.
Title: Re: P0115 Engine temp circuit malfunction
Post by: dave the builder on 22 November 2020, 16:01:55
an overfueling issue could kill the cat ,a thermostat issue could take out the headgasket or worse
"warning lights are for a reason .not just till christmas"   ;D
Title: Re: P0115 Engine temp circuit malfunction
Post by: terry paget on 22 November 2020, 16:25:49
an overfueling issue could kill the cat ,a thermostat issue could take out the headgasket or worse
"warning lights are for a reason .not just till christmas"   ;D
You infer I should send her to a local garage without delay. Some warning lights, e.g. emissions provoked, are just advisory, and go out after 25 or so engine restarts. I have known them for 20 years on many Senators and Omegas.
Title: Re: P0115 Engine temp circuit malfunction
Post by: dave the builder on 22 November 2020, 16:34:51
an engine management light is an immediate MOT fail
an engine management light is there to warn the driver that there is an issue with the emission system and needs looking at BEFORE damage to the cat or engine occurs

does the temp gauge go up when the engine is warm ?
do the rad fans run constantly ,even when the engine is cold (if the CTS id dead or unplugged the ECU defaults to run the fans)

can you/your family member get live data on the code reader .if you can .follow Nicks advice  ;)


Title: Re: P0115 Engine temp circuit malfunction
Post by: Nick W on 22 November 2020, 17:07:02
Modern cars are a lot more reliant on sophisticated systems than older ones, and they're also a lot more delicate. They certainly don't take overheating at all well, so some proper diagnosis now should be a priority.



Title: Re: P0115 Engine temp circuit malfunction
Post by: ronnyd on 22 November 2020, 17:19:26
2008 Astra 1.6 petrol manual saloon

Daughter has now found the diagnostic socket on her Astra, and the above fault code has been displayed.
It first appeared last Monday, with no apparent car problems. She used the car in the week, on Friday evening it started hesitantly, cranking slowly but starting eventually, she got it home and rang me. This morning she found the socket, and got the above fault. The engine did start this morning.

Before I expected either dying battery or failed alternator, not so sure now. I am in Somerset under lockdown, she is in Enfield, 120 miles away.

Please advise.
What lockdown is that Terry. Took SWMBO for an eye test today and traffic and car parks were busy as normal. I went for a walk away from the herd while she was in Specsavers and high tailed it home as soon as she finished. :D I suppose that Zummerzet to Middlesex , (showing my age there  ;))  may be stretching things a bit far though. :-\
Title: Re: P0115 Engine temp circuit malfunction
Post by: dave the builder on 22 November 2020, 17:24:24
Eye tests are classed as essential travel  :)  the police won't bat flu an eye lid   :-X
Also car repairs  ;)
Title: Re: P0115 Engine temp circuit malfunction
Post by: Doctor Gollum on 22 November 2020, 17:29:53
2008 Astra 1.6 petrol manual saloon

Daughter has now found the diagnostic socket on her Astra, and the above fault code has been displayed.
It first appeared last Monday, with no apparent car problems. She used the car in the week, on Friday evening it started hesitantly, cranking slowly but starting eventually, she got it home and rang me. This morning she found the socket, and got the above fault. The engine did start this morning.

Before I expected either dying battery or failed alternator, not so sure now. I am in Somerset under lockdown, she is in Enfield, 120 miles away.

Please advise.
What lockdown is that Terry. Took SWMBO for an eye test today and traffic and car parks were busy as normal. I went for a walk away from the herd while she was in Specsavers and high tailed it home as soon as she finished. :D I suppose that Zummerzet to Middlesex , (showing my age there  ;))  may be stretching things a bit far though. :-\
It doesn't look that far on the map :D
Title: Re: P0115 Engine temp circuit malfunction
Post by: Nick W on 22 November 2020, 17:34:22
2008 Astra 1.6 petrol manual saloon

Daughter has now found the diagnostic socket on her Astra, and the above fault code has been displayed.
It first appeared last Monday, with no apparent car problems. She used the car in the week, on Friday evening it started hesitantly, cranking slowly but starting eventually, she got it home and rang me. This morning she found the socket, and got the above fault. The engine did start this morning.

Before I expected either dying battery or failed alternator, not so sure now. I am in Somerset under lockdown, she is in Enfield, 120 miles away.

Please advise.
What lockdown is that Terry. Took SWMBO for an eye test today and traffic and car parks were busy as normal. I went for a walk away from the herd while she was in Specsavers and high tailed it home as soon as she finished. :D I suppose that Zummerzet to Middlesex , (showing my age there  ;) )  may be stretching things a bit far though. :-\
It doesn't look that far on the map :D


Detour via Barnard Castle
Title: Re: P0115 Engine temp circuit malfunction
Post by: Doctor Gollum on 22 November 2020, 17:37:01
That might be a smidge further :D
Title: Re: P0115 Engine temp circuit malfunction
Post by: Nick W on 22 November 2020, 17:38:39
But it does have government approval. For what that's worth
Title: Re: P0115 Engine temp circuit malfunction
Post by: terry paget on 22 November 2020, 18:57:38
Thanks for all advice. Answering your questions:

Astra has no temperature gauge. Catherine did not comment on the fans running from start up, but she would not have noticed.

She cannot read live data on her basic reader. I can on mine, but the car is not here.

Google Maps reckons it is 143 or 153 miles from Midsomer Norton to Enfield.

My wife has ruled that I must not drive there while under lockdown. When I had 6 Senators or 6 Omegas I would drive the spare one to Enfield when Catherine's car misbehaved. Now I run Astras and Merivas they are less reliable and I am older.

Are we all agreed that the fault is the thermostat, as IanSoutham believes? It makes sense to me. I have changed two on Merivas, not a big job. I don't know garages in Enfield, Catherine fancies Greenfox. Should I send her there, with instructions to change the thermostat, or ask them to diagnose the fault and rectify it, suggesting thermostat?
Title: Re: P0115 Engine temp circuit malfunction
Post by: Doctor Gollum on 22 November 2020, 19:33:58
Either book it in and get it done or wait ten days and DIY...

That garage seems to be well reviewed, so may be the best bet ;)
Title: Re: P0115 Engine temp circuit malfunction
Post by: Nick W on 22 November 2020, 19:43:13

Are we all agreed that the fault is the thermostat, as IanSoutham believes? It makes sense to me. I have changed two on Merivas, not a big job. I don't know garages in Enfield, Catherine fancies Greenfox. Should I send her there, with instructions to change the thermostat, or ask them to diagnose the fault and rectify it, suggesting thermostat?


No, because without some simple work it's a guess. And that is a shitty way to fix anything.
It could be the thermostat, or the sensor, or the wiring, or the moon out of alignment.


If you can't fix it for her, have your daughter book into her favoured garage and explain the symptoms she originally noted AND NOTHING ELSE!!!! Then they can fix it properly
Title: Re: P0115 Engine temp circuit malfunction
Post by: Marks DTM Calib on 23 November 2020, 12:57:57
So first things first

Battery - needs charging and/or replacing - slow crank, never good and can trigger all sorts of other incorrectly flagged DTCs

For the DTC there should be more than just P0115 (there certainly will be if you do the pedal test), I would expect an extra two digits which gives the symptom, the first four only identify the circuit at fault.

No diag can be made without these two items, any other suggestions are just random guesswork