URGENT! Coolant temperature sensor error.

petrolhead

Hi!

Dashboard showed up a CLT sensor error. Replaced sensor and car doesnt run anymore. Dashboard shows 120 degrees. Checked resistance of the CLT sensor it's ₂.5kOhms - about where it needs to be according to the ambient temperature and the resistance graph.
I also checked the wire continuity, everything seems to be fine.
I suspect that ECU is damaged, because before the coolant error my idle was jumping from 800 - 3000 rpm. Checked ICV and wiring, everything also seems to be allright.
Please help.

KielMiller

petrolhead

What software and pcb version?

petrolhead

KielMiller
Firmware is 4.1.5, and i'll check the PCB version, when I'll be home. IIRC it was 2.5? but yeah, i'll check later today in the evening.

petrolhead

Measuring resistance between pins B7 & C8 reads 66.1kOhms

JHM

Probably a broken ground issue.

Measure voltages:

battery minus - cylinder head
battery minus - ecu ground pin

ideally, should be millivolts

petrolhead

The ECU ground seems to be faulty.
Measured 4.8mV from battery negative to head.
Measured 11.9V from battery negative to ECU pin D8 (ground)

Disconnected battery and measured resistance from the negative lead to D8 pin - 387 Ohms

Any suggestions what to do next? Where to look for the fault in wiring?

KielMiller

petrolhead

It would be in your best interest to look through your wiring and find the ground issue.

petrolhead

KielMiller
The harness visually looks good. But yeah, i will go through the wiring. Thanks!
It's just wierd that MAP readings seemed fine. It should also use ECU ground right?
Injectors also have ECU ground on one of the pins, right?

petrolhead

Ok, i'm a dumbass, because i measured A8 pin not D8.
ECU ground is good.
From battery negative terminal to pin D8 measures 1.3mV

Sometimes the CLT reading is 120 sometimes 40

Resistance measurement from engine head to pin B7 is 2.9kOhms

Intake air temperature in dashboard shows 53 degrees, but its now around 15 degress.

petrolhead

Well, i could bet 99% that it's ECU fault.

Maybe i should try to do a firmware update?

petrolhead

I updated firmware to 4.1.6, but to no avail.
The error is still there.
Now IAT reading in dashboard was +/- correct
CLT sensor error, temperature = 40deg.
took a screenshot of diagnostics tab, noticed that CLT voltage = 0

Before when it showed 120deg temperature, there wasnt any errors.

JHM

Have you seen this troubleshooting guide?
https://invent-labs.com/jetronic/docs/en/setup/firststart.html#temperature-sensors

petrolhead

JHM
Standart ECU is the one that provides voltage to signal wire?

JHM

petrolhead
Yes this is how the standard wiring works.

petrolhead

JHM
Ok, that helps a lot, maybe stock ecu connector doesnt have a solid connection.
Fingers crossed that this would be the fix.

petrolhead

JHM
Thank you! The problem is fixed.
After splicing wires to stock ECU connector, i was unable to get it fully inside the housing. I plugged it in, however because it wasnt fully in the housing, the metal latch on the ECU did not lock the connector in place.
And so after almost a year it had came loose.

Thank you JHM and KielMiller for your help, much appreciated 👍