: Fault code P0115 - mysterious coolant temp problem

Chris Watts
23-01-2012, 18:04
I had the emissions light come up on the dashboard around a week ago - fault code P0115 (Engine Coolant Temperature Circuit Malfunction). The blower has also not been getting as hot as it used to. http://www.astraownersclub.com/vb/images/smilies/confused.gif

I took it to Kwik Fit who suggested that I pay 35 for their "diagnostic check" which took 2 minutes and said the thermostat sensor needing replacing (a cost of 90 fitted). I did some research and have seen several threads with people saying that this component was replaced on their cars many times and didn't resolve the issue - with the engine management light coming back on again shortly after. http://www.astraownersclub.com/vb/images/smilies/icon_exclaim.gif

Decided to take it to a local garage specialising in Vauxhalls and parted company with another 42 for their Tech2 diagnostic check. To be fair the guy spent a decent amount of time looking over the problem, and has come to the conclusion that a wiring loom needs replacing (70-80 fitted).http://www.astraownersclub.com/vb/images/smilies/icon_neutral.gif

He said he ran a check on the blower and it was running as expected (around 40 degrees). When I got in the car and drove off the blower was roasting - much much hotter than it has been getting so I think he was given a different picture! http://www.astraownersclub.com/vb/images/smilies/icon_eek.gif

Basically cash is tight at the moment and I've already blown 77 on diagnostics without a thing being replaced. Has anyone had any experience of a similar issue? I was wondering if the fact the engine was running in the workshop (not moving) would account for the blower being a lot hotter when I drove it off? http://www.astraownersclub.com/vb/images/smilies/confused.gif

Would the wiring loom or the temp sensor affect the blower temp? Seems unusual... my best hunch was a sticky thermostat but now I'm totally confused!http://www.astraownersclub.com/vb/images/smilies/icon_cry.gif

24-01-2012, 12:53
Thread should be showing now.

I've edited your posts as we can't read black lettering on a dark skin.

Welcome aboard.

24-01-2012, 14:41
When you say thermostat sensor, did they actually change the thermostat housing? There are two sensors in there and the one that fails most often is the one that only comes with the stat.

I take it you've got some sort of 1.6/1.8 twinport or VVT engine?

24-01-2012, 15:59
Hi mate. I have the same code as you. Same situation too, blower doesn't get that hot quickly.

My Emissions light came on a few weeks after buying the car, then went off after a few days. Then came back about 2 months ago, went off around a week later and hasn't come back since. Still have the error code but no emissions light.

User from a previous thread had the same symptoms as myself, and bought a new thermostat which fixed the problem for him. I haven't gotten around to it, but I intend to do the same pretty soon. Check this thread below:


I found a resource on the web about a guy who had the same issue as all three of us and used an OBD2 reader to keep an eye on his engine temp during a drive. I don't know what software he is using (anyone have any ideas?) but I do know that an OBD2 reader can be got off ebay very cheap. Might be a good place to start if cash is tight. You can check to see if the car is warming up quickly enough, or if anything funny is going on. If that's the case, your thermostat is probably stuck slightly open. Nothing too major but symptoms are what you have been describing (I have them too). Here is the resource:


I'm no expert, but have been doing a lot of research. I will probably replace mine over my Feb holidays after mock exams.

Chris Watts
30-01-2012, 14:43
[Accidentally posted twice - deleted duplicate]

Chris Watts
30-01-2012, 14:43
I have a 1.6 Astra SXi Twinport 2006 (Z16XEP).

The day after posting, the emissions warning light went off - but as you report the error code is still stored, confirmed by running the "pedal test". Pretty sure the blower is back to it's poor performing self again - but often with these things you end up doubting yourself!!

I also came across the article you linked to which hits the nail on the head. Also the solutions he was offered mirror the ones I was given - i.e. new thermostat sensor / new wiring loom.

I came to the conclusion that I needed to know what temp the engine is getting to, but rather than getting an OBD2 reader, there is a hidden service/test menu that can be accessed which will give you the operating temp of the engine (on my model this is reached by holding down the "Settings" button until you hear a beep and then pressing the right hand button beneath the clock).

I've been watching the temp for a few days and it barely gets above 60 degrees - which is exactly the same as that guys article before he replaced the stat. In his graph it peaks around the 60 mark and I notice that in the picture at the end of the article (after the stat is replaced) his operating temp shows 104 degrees.

Just to make doubly sure about getting the thermostat replaced (given it's so pricey) I've asked a friend who has the same model and age Astra as me to monitor his temp in the same way so I can compare with his. I'll post up the result.

Then I think it will be a case of requesting the garage replace the thermostat and leave the wiring loom well alone!

Chris Watts
31-01-2012, 08:11
Update this morning - my friend reports his temp was up to 85 degrees after 10 mins (exact same car/engine as mine), and my brothers Zafira hit 94 degrees within 10 mins too. Definitely getting my stat replaced.

Chris Watts
03-02-2012, 20:32
Just to close this one out... I took car to my local garage today and they replaced the thermostat - 139 fitted, engine temp hit over 100 degrees within 10 minutes of driving it away + blower pumping out lovely hot air! Wonderful! Fault codes also cleared and no emissions light. Pretty sure it will stay that way. The garage were adamant that a wiring loom would need to be replaced to stop the emissions light from coming back on, they were sure that a dodgy thermostat wouldn't cause that warning light. My theory however (after reading a fair few posts online etc) was that the temperature sensor in the engine throws a fault when the engine temp is so low, as it assumes it can't be correct (pre-repair my engine was running at about 40 degrees!) Hopefully this helps people going forward. In short, if you have the following symptoms:

- Blower blowing lukewarm air
- Emissions warning light on
- Fault code 0115
- Engine temp not getting over 70 degrees within 10/15 minutes of driving

... don't waste time having diagnostic checks etc - just inform the garage you would like a new thermostat. You'll save yourself a load of cash!

03-02-2012, 20:41
There are 3 temperature senders in the system and the car constantly compares the readings to what it is expecting. A stuck stat, or other fault which means the readings don't match what the car is expecting will fire the code up and bring the light on.

Cars are too clever for their own good nowadays and not every independent garage is up on the new technology (hence the comment about dicky stat not causing the light).