P0128 2 weeks after replacing temp sensor

[JonathanLondon]

Hi

I have a 14-plate 1.6 Astra Auto.

Recently got the "AC Off Due To High Engine Temp" warning, and an OBD II dongle said it was a P0128.  At the same time the temp gauge went to minimum.  Checked under the bonnet and the fan wasn't running even though we watched the coolant temp run up past 90C.

I'm no mechanic, but my local independent garage swapped out the engine temp sensor, topped up the coolant, cleared down the error code, and everything was back to normal.  Indeed after driving home from the garage, the fan was running and the coolant was around 80C.

Two weeks later, and the warning has come on again, on the same journey at the same point (about 20 mins from cold).  I doubt the new sensor (genuine Vauxhall part) has failed.  One additional clue is that on both occasions, the car had been washed a few hours earlier, but I really doubt that it's water ingress causing the problem.

My guess is that may be there's a loose or damaged wire, and that replacing the stat was a temporary fix.  The car has done less than 30,000 miles.

Any clues?  Torn between taking it back to the local (friendly and very helpful) independent garage, or taking it to Vauxhall (which will be difficult as I am avoiding public transport due to the virus).

Thanks!

[Rusty2009]

I would go back to the local independent garage much cheaper on your wallet.

But as they have supplied and fitted the part it should be down to them & their warranty (If the sensor is faulty).

[JonathanLondon]

I would go back to the local independent garage much cheaper on your wallet.

But as they have supplied and fitted the part it should be down to them & their warranty (If the sensor is faulty).

Rusty, many thanks for your advice.  I actually contacted my local-ish Vauxhall dealership yesterday.  They want £99 to run diagnostics before they can tell me how much it will cost to repair.  And they can fit me in for the pick-up/drop-off service in October, or offer me a loan car in September.

Then I spoke to the local independent who are a short walk away who will look at the car tomorrow.  No contest.   The original repair there was £110 all in. They think it's unlikely to be the sensor again.  We'll wait and see.  (Previously the same Vauxhall dealership sent them the wrong part, and then it took a week to send the right part as they were merging their parts depot with Peugeot Citroen - happy days!)

If it's not the sensor, any thoughts on what else it is likely to be?

Thanks
Jonathan.

[Rusty2009]

Local stealerships are a p.i.t.f.a & they never really do anything other than plugging the computer on and go off that (they never look into why or what truly is causing the fault) & most of the time will just say there is a software update which fix the issue (which it doesn't).

In terms of if it's anything else you say it's happened after you've washed the car so that would make you think it's not a faulty sensor (although they do get faulty batches of sensors).

The wiring would be a good place to inspect, really they need to fully understand the system and how it works, run simulating tests to prove the fault and that the fix will work.

[JonathanLondon]

Local stealerships are a p.i.t.f.a...

Many thanks for your continuing advice.  The garage report that the thermostat is not closing properly and as a result the engine isn't getting up to temperature and hence the P0128 error triggers after 23 minutes.  They were suspicious about how long it was taking when they replaced the temperature sensor (at my request), a couple of weeks ago.

They have asked Vauxhall to quote for the thermostat, and await Vauxhall's return call.  Locally Vauxhall parts are on a seven working day lead time, and that's once they get around to calling you back.