Vauxhall/Opel/Holden Astra G / Mk 4 / TS - Cooling system warning light (Coolant temp sensor)

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Sun 7 Jan 2018 05:17
Vauxhall/Opel/Holden Astra G / Mk 4 / TS - Cooling system warning light (Coolant temp sensor) - Myddraal

I've got a 2001 Astra with the X/Z18XE Engine, with the Simtec 71.1 ecu. It's throwing a cooling system warning light, but nothing actually seems to be wrong with the car. I wouldn't care, but I want to sell it.

Coolant is pumping, the fans are turning on and off, the A/C works great even on a 43°C day like today. It quickly heats to 90°C and stays there in all conditions.

The temperature sensor (thermistor) doesn't seem to have an abnormal temperature/resistance curve, but I've ordered a new one anyway. I've bought a wide range thermometer and I'll plot calibration curves for the old and new sensor when it arrives. The connector has a really nice 4.98V across the pins, the ground has good continuity to the negative battery terminal.

My cheap OBD2 reader didn't pick anything up (KWP2000 protocol). This car does not do the 'pedal test' nor the 'paperclip test'.

I got it scanned with a fancypants Bosch KTS-340 which gave me:

Simtec 71 -------- 1
P0115 Coolant temperature sensor
Radiator fan ctl. unit 3.0 ------- 3
44 Emission warning lamp (MIL) -------- Signal too small
2 Coolant temperature sensor ------- signal improbable
164 Coolant temperature sensor -------- signal improbable
164 Coolant temperature sensor -------- signal improbable

To make matters worse, it seems to be intermittent.

It does have the cooling module between the FL wheel well and bumper, but I can't figure out how to disconnect the plugs, and I can't see any obvious ground connections, let alone loose or corroded ones.

I'm pulling my hair out. Any help to stop me going bald would be very much appreciated.

Edited by Myddraal on 07/01/2018 at 05:19

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Sun 7 Jan 2018 18:19
Vauxhall/Opel/Holden Astra G / Mk 4 / TS - Cooling system warning light (Coolant temp sensor) - elekie&a/c doctor

If the cooling fans and a/c are working correctly,and the engine temp gauge is giving the correct reading,then it is unlikely to be a temp sensor fault. The cooling fan modules do give trouble,and i suspect this is the issue.The connection plugs to the module are released by sliding the locking bars sideways.(very often red in colour)The earth point is up near the battery.

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Thu 18 Jan 2018 08:05
Vauxhall/Opel/Holden Astra G / Mk 4 / TS - Cooling system warning light (Coolant temp sensor) - Deon Pheiffer

Thanks for informing how to get engine temperature cooling module plugs off

I too have a very strange problem......

I have a new problem with my 2002 Astra is also (again) playing up.


Latest problem: Overheat light (square box with a + sign) lights up in amber on instrument panel - indicating overheat condition. This is NOT so! I ran OPCOM (plugging in an adaptor to the plug in the centre console, and running the sofware on my laptop whilst the engine is running. It is totally amazing the amount of accurate data this software provides!). Anyhow, this indicates my coolant temperature rises to 90 degrees, then the radiator fans kick in, which then stops the rise in temperature, and the temp then fluctuates between 88 and 90 degrees. ( This I understand is the normal operating temperature for this engine (X18XE).
Here is the problem: this overheat light then stays ON forever. (Although I KNOW the coolant temperature is normal!). Added problem: whilst this indicator light is ON, it removes power to the temperature gauge on the instrument panel, which means I cannot physically see the operating coolant temperature - it shows zero.
I have:
1) replaced the thermostat a while ago. Taken it out since (a few trimes) and with the aid of boiling water checked it: it is working fine. I drilled a 5mm hole in the thermostat the ensure some water passes thru the engine at all times.
2) Reversed flushed the engine and radiator with hose water, albeit both in situ: lots of little black thingys came out of the radiator. Refilled with correct anti freeze (very expensive) and bled correctly (I think)
I think now I need to replace the coolant temperature sensor. Maybe is it activating too soon? (certainly it is allowing both electrical fans to kick in around 90 degrees - surely this should be higher?). Could perhaps also be a sticky relay in the engine coolant controlling computer (expensive item to replace, me thinks.....). I am also taking my car to a radiator place today for a complete pressure test of the coolant system.
Anybody with any ideas?

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