Technical Desperate for help with P0115 error code

[ConnorODT]

Hello,

So I’m struggling to fix a P0115 error code. I’ve changed the sensor and today I have also changed the Pig end connector. Nothings changed, still getting the same issues. The temperature sensor is currently reading -40 degrees so it is obviously wrong somewhere.

I’ve been told by your favourite AI that it’s likely the wire broken somewhere else, but other than the connector to the ECU which seems strange, it would be spliced into other sensor and presumably wouldn’t work at all. The coolant seems fine, but I haven't bled the system.

Any advice, help or maybe I’ve just done a real poor job of the repair. Driving me crazy, I’ll try anything!

Thanks, Connor

 

[ConnorODT]

Also, just to add - I changed the earth strap using an eBay part but did not mess with the strap under the battery tray.

 

[JD2023]

Have you checked the wiring from the boot lid
Theses are known to break and short and give weird issues

 

[JD2023]

It is the bit under the battery tray between the chassis and the gearbox that corrodes
So that is an area you need to check / replace while your in there
It is not a big job but one worth doing to rule it out

Also have a look at this thread as it suggests that the coolant needs to be flushed after replacement

Engine won't start. Computer code P0115. What to do? [Pics] | FIAT 500 (2007+)

Hi everyone. New here. 2014 Fiat 500 1.2 Liter. Engine won't start. (it did start twice but choked very quickly) Connected a car computer (which my nice neighbor had). Showing this code: P0115 engine coolant temperature sensor 1 circuit I also checked DATA STREAM on computer: Noticed ECT...

www.fiatforum.com

 

[jackwhoo]

If you are reading ecu live data and engine coolant reading -40 c then likely wire broken in loom between sensor and ecu. Prove by continuity test of sensor wire ect sensor plug to ecu plug.

Strange this has come up twice in last couple weeks with different op names?

 

[John202020]

The temperature sensor is currently reading -40 degrees so it is obviously wrong somewhere.

What is indicated on the dash display? Normal running temp?

 

[ConnorODT]

If you are reading ecu live data and engine coolant reading -40 c then likely wire broken in loom between sensor and ecu. Prove by continuity test of sensor wire ect sensor plug to ecu plug.

Strange this has come up twice in last couple weeks with different op names?

Definitely the first time I have posted. Yeah it seems like the -40 reading is almost certainly a broken wire. I’ll do some continuity tests in the morning to confirm.

 

[ConnorODT]

What is indicated on the dash display? Normal running temp?

It seems to be intermittent, but I am relying on my girlfriend noticing that the temperature is or is not working, which is very unreliable. Since I’ve been looking, the temperature doesn’t seem to be showing at all.

 

[ConnorODT]

Have you checked the wiring from the boot lid
Theses are known to break and short and give weird issues

It does have a boot wiring issue yes, the wiper was playing up and the boot only opens with the key. It’s certainly another avenue worth exploring! Once I’ve ruled out a break in the circuit (given the -40 reading) I’ll move onto this if nothing improves. Thanks for the advice

 

[The Panda Nut]

If you are reading ecu live data and engine coolant reading -40 c then likely wire broken in loom between sensor and ecu. Prove by continuity test of sensor wire ect sensor plug to ecu plug.

Strange this has come up twice in last couple weeks with different op names?

The first one seemd to establish that -40 indicates no sensor / signal from it. In that case the sensor was not fitted to the car, and the OP was trying to upgrade the dash I believe. It suggests new thermostat and sensor may be needed.

 

[ConnorODT]

The first one seemd to establish that -40 indicates no sensor / signal from it. In that case the sensor was not fitted to the car, and the OP was trying to upgrade the dash I believe. It suggests new thermostat and sensor may be needed.

I did change the sensor, thermostat does seem to be coming up often, I’ve just strayed away from it just because the fault indicates a circuit issue, which I don’t see why it would be for the thermostat? But clearly evidence from other people suggests it’s very much possible. Although I have seen P0128 and P0116 codes for the thermostat which would be on instead?

Thanks for the help!

 

[jackwhoo]

Posts 5 and 7

 

[ConnorODT]

Just a little update on this, I have spliced the wires, the 5v is working down to the connector but I’m not seeing any resistance on the other wire. So my only option is to splice as close to the ECU as possible, and hope that works or I’m going to have to accept it’s the connector pin for the ECU.

I have validated it is not the ECU itself (the internal earth) because the MAP and other connected sensors are working fine. I have found the connector pin (no.58) and probed it to the splice and I’m still getting an open circuit, so it appears the fault in somewhere in that section, either the connector or remaining wire.

Quite possibly the worst thing I’ve ever had to fix, a real pain in the arse.

 

[jackwhoo]

Do you mean there is no continuinty in signal wire from ect sensor and ecu plug?
IE wire is open circuit?

 

[ConnorODT]

Do you mean there is no continuinty in signal wire from ect sensor and ecu plug?
IE wire is open circuit?

So I have spliced in around 20cm from the ECT plug, I know everything below that point is working fine (checked the resistance on the coolent sensor, I have ran new cable with a new pigtail connector on which I checked for continuity). The temperature is still reading at -40, but I’m getting 5v through the one wire so I’m confident that the 5v cable is working.

I then tested the splice point into the ECT connector (it’s the Bosch sided mounted ECT) and I couldn’t get any continuity just an open circuit. From my research there doesn’t seem to be any resistors or anything in the connector, so I should be able to get a closed circuit. So my guess is that somewhere from the splice point to the ECT connector is broken, or the ECT pin itself is broken.

Open to correction or any advice though.

 

[jackwhoo]

I cannot work out what you have done .

You need to check the ecu plug connector to the ect sensor plug the wire between these points must be intact , near zero resistance.

You must make sure you are using the correct wire connector at the ecu plug

 

[ConnorODT]

I cannot work out what you have done .

You need to check the ecu plug connector to the ect sensor plug the wire between these points must be intact , near zero resistance.

You must make sure you are using the correct wire connector at the ecu plug

I have bridged across the points with a paper clip, but I’m still not seeing any temperature change when I test the live feed. The circuit is fine, I have checked all the way from the ECT pins to the ECU pins on both wires.

I have literally no idea what is causing this fault. Car is very much going to end up in the bin over this silly little sensor.

 

[jackwhoo]

I have bridged across the points with a paper clip, but I’m still not seeing any temperature change when I test the live feed. The circuit is fine, I have checked all the way from the ECT pins to the ECU pins on both wires.

I have literally no idea what is causing this fault. Car is very much going to end up in the bin over this silly little sensor.

Are you 100% sure you are connecting to the correct wires at ecu plug?
Do not just go by wire colours find a pin out for your ecu plug and find out if the pin out is viewed front or rear.
Are you disconnecting the plug from the ecu to check continuity between ecu plug connectors to ect plug connectors?