Technical Fault code P0115 temp sensor wiring

[Woodchip]

Punto 2001 Mk2 1.2 8V showing P0115 code. Here's a bit of history: engine overheated while teaching daughter to drive - lots of low gear slow stuff!

Steam out of the expansion tank but the fan didn't cut in until engine turned off & then only for a few secs. The temp warning light on the dash did not come on! No fault code showed.

Thermostat is working so I tested the coolant temp sensor in a pot of water on the hob - values were way off. I've changed the sensor for one out a scrappy (fairly good values in the hob test), filled & bled the coolant. I used Multiecuscan to activate the fan so that is OK. I could not get it to activate the dash engine temp warning light using the "Engine" module but it would activate using the "Dashboard" module. Is that normal?

I then started the car & the engine temp light came on along with the Fault code present light: code is P0115 "water temp sensor" signal high/fatal/light on.

The engine warmed up OK, got to 75C (on Multiecuscan screen) and the fan cut in, holding the temp steady at 75C.

I think the sensor is OK so I'd like to test the wiring. So the big question is: where do I find the other end of the wires? If it's at the ECU which connectors?

I hope someone can help.

 

[Brendan W]

https://www.fiatforum.com/punto-ii/283445-mk2-1-2-8v-2003-ecu-wiring-diagrams-wanted-urgently

Try pdf linked in post #5 of this thread - it is 2003 but probably the same.

 

[Ziggy122]

What values did you get at what temperatures?

Also 75Deg C is too low for the fan to kick in

it doesn't kick in till about 90degs C

Ziggy

 

[Woodchip]

Wiring to ECU pin A29 is good but I could get no continuity to pin 5. I would have probed all the ECU pins just in case 2001 is not the same as 2003 but I didn't have time. My meter probes are too thick so I'm going in via a paper clip! I'm now assuming the wire is good or there would be no signal at all.

k Ohm values are:
Temp (C) ....... Haynes ........ Old Sensor .......... New scrappy sensor
40 ..................... 1.15 .............. 1.23 ............................. 1.10
50 ..................... 0.80 .............. 1.01 ............................. 0.85
60 ..................... 0.57 .............. 0.70 ............................. 0.62
80 ..................... 0.30 .............. 0.44 ............................. 0.36
90 ..................... 0.24 .............. 0.34 ............................. 0.28
100 ................... 0.17 .............. 0.27 ............................. 0.24

So the "new" one is better than the old but not perfect. Plus, the "new" one lights the management lamp, the old one does not ( tried reconnecting it)

So I'll get a split new sensor & try that. The old sensor was the bonded into the plastic pipe assembly type, the scrappy one is the assembly with the screw in type sensor; so £5 for that plus about £8 for the sensor is still better than about £34 for the old assembly replacement.

 

[Ziggy122]

From ECU A29 - goes to ECT1
From ECU A5 - ECT pin 2

If your getting a continuity from pin 29 to 1 = Thats fine
But not getting anything from Pin 5 to pin 2 - thats not a good sign

Either you need to retest to ensure a good connection - or there is a break in the wiring somewhere

Since the fault code is for P0115
Engine coolant temperature (ECT) sensor - circuit malfunction

i wouldnt have bothered to look or blame the ECT
The range will change slightly from the book figures
As there is always going to be a slight difference in the multi-meter, the age of the thermister - the temperature guage you use to read the water temp

They didnt look THAT bad to me....

I'd be seriously investigating that ""malfunctioning"" pin

Ziggy