hi i have this fiat grande punto 1.4 tjet from 2008
i just bougth the car a coupel a months ago. when i put the obd tester on the car, i get a error on the heater circuit. and what could see the previus owner had change the o2 sensor. but it was a uogrianl one. so i changedit with a bosch one but i still get the same problem.

when i mesure the 2 white wire on the o2 sensor i only get 8volt output when the o2 sensor i pluged off. and when i put load on i its drob to abut 0. i have chek the wires its not the wire. its the same at the output of the ecu. my question is can it be a fuse. i have try to look at it with a circiut tester but not put out look and put back.

my o2 sensor newer gets heated so it cant messure a/f ratio


sry for my bad english

Forgive this BUT did you clear the original fault code?

yes i have.

when i mesure betwen pin 3-4 on o2 sesnor plug its say 8 volt unloaded an 0 when it loaded but if i mesrue betwen pin 4 and ground its says 12volt.
so it should be pin3 wire thats problem when i look at the diagram its go to ecu pin 16 but its not seen to be the wire but i have try with another ecu used one its make the same problem. o2 sensor stay at 465mv
the resistans on o2 sensor is 10ohm

webmusta said:

when i mesure betwen pin 3-4 on o2 sesnor plug its say 8 volt unloaded an 0 when it loaded but if i mesrue betwen pin 4 and ground its says 12volt.
so it should be pin3 wire thats problem when i look at the diagram its go to ecu pin 16 but its not seen to be the wire but i have try with another ecu used one its make the same problem. o2 sensor stay at 465mv
the resistans on o2 sensor is 10ohm

Click to expand...

Not very clear... do you mean unconnected (on sensor side) ?
Both sensors receive +12V @ pin 4 from the distribution box, thru the T7 relay and F27 fuse, the fuel vapour recirculation solenoid is powered by the same line. Pin 3 is grounded thru the ECU which by this can control the heaters status. Pins 1 & 2 are the O2 signal going to the ECU.

Cheers, Bernie

webmusta said:

when i mesure betwen pin 3-4 on o2 sesnor plug its say 8 volt unloaded an 0 when it loaded but if i mesrue betwen pin 4 and ground its says 12volt.
so it should be pin3 wire thats problem when i look at the diagram its go to ecu pin 16 but its not seen to be the wire but i have try with another ecu used one its make the same problem. o2 sensor stay at 465mv
the resistans on o2 sensor is 10ohm

Click to expand...

That would mean the ecu isn't grounding the sensor.
the difference in voltage means the ECU doesn't have a good ground. Measure what voltage you get from ECU body to battery negative (if ECU has good ground you will see ZERO volts) but you need to have the ecu loaded.... put a small bulb in the O2 heater circuit

It doesn't look like a fuse issue. If you can measure 12v from pin 4 to ground with a load(a bulb), then it's a grounding issue.

I don't think it's fused from the ecu to sensor.
But there are multiple fuses for the ecu... so maybe one of these.

what did you use for load testing?
I recommend using a 10-20w 12v bulb as a load. Don't use the sensor... just in case it's shorted inside.
The bulb will tell you immediately if the circuit can carry current, will tell if a circuit looses continuity when moving/pushing wires...etc



have a look at these fuses diagrams:
https://www.autogenius.info/fiat-grande-punto-2006-2012-fuse-box-diagram/
https://www.autogenius.info/fiat-bravo-2008-2014-fuse-box-diagram/

Engine and ECU is the same from the bravo... so fuses might be similar as well.

i use the o2 sensor for load

Pull-out pins 3 & 4 @ sensor's plug and connect a 5 watts bulb directly to the two pins, the bulb should lit when engine is running.
DO NOT use another bulb for this kind of test or you might blow the ECU's pull-down stage by draining too much current !!
If the bulb doesn't lit, leave pin 3 connected to it and connect the other side direct to battery positive: if bulb is still off the return path (thru ECU) is bad, either wire or plug or ECU itself. If the bulb lits, check the other side; connect pin 4 to the bulb and the other side direct to ground: if the bulb doesn't lit, the positive path is bad (wire, fuse, connection @ fusebox).
Use a (very) thin flat screwdriver to release the pins locker if you don't have a pin extractor (full set on Alixxxxxx for a few €).

BRs, Bernie

If someone here helped You fix -or better, understand- your issue, hit the thanks icon @ bottom right corner, it's free and makes us feel helpy ;-)

Bernievarian said:

Pull-out pins 3 & 4 @ sensor's plug and connect a 5 watts bulb directly to the two pins, the bulb should lit when engine is running.
DO NOT use another bulb for this kind of test or you might blow the ECU's pull-down stage by draining too much current !!
If the bulb doesn't lit, leave pin 3 connected to it and connect the other side direct to battery positive: if bulb is still off the return path (thru ECU) is bad, either wire or plug or ECU itself. If the bulb lits, check the other side; connect pin 4 to the bulb and the other side direct to ground: if the bulb doesn't lit, the positive path is bad (wire, fuse, connection @ fusebox).
Use a (very) thin flat screwdriver to release the pins locker if you don't have a pin extractor (full set on Alixxxxxx for a few €).

BRs, Bernie

If someone here helped You fix -or better, understand- your issue, hit the thanks icon @ bottom right corner, it's free and makes us feel helpy ;-)

Click to expand...

Hello Bernie. I like this post a lot. As you may have gathered from my other posts I'm most confident when wielding a big hammer or levering something with a screwdriver! I'm not too bad with common electrics but electronics, especially ECUs, frighten me because it's so easy to burn something out!

My normal approach to a suspect O2 sensor is first to see what MES (or my VAG/COM if its a VAG, or my last resort generic code reader for others) tells me and stream/graph live output if I can. Fault finding O2 sensors isn't something I do often - they seem quite reliable - but of the ones I have been involved with it's often the heater circuit which is burnt out and can be easily checked with a multimeter. I like your "belt and braces" light bulb approach though. I would immediately think "voltmeter" in these circumstances but I think your bulb is a better solution because, unlike the voltmeter, it will put load on the circuit - Given that you don't overload it with too big a bulb!

So, thanks very much. I'm going to write down your procedure in my little book of "useful things to know"

Kind regards
Jock

hi i have now tryit with a 5w bulp. betee 3-4 nothin happens.
3 to batt+ the light bulp blink
between 4 and groud ligts its on

my bad between 3-4 the light blinknig

and if its the ecu can i use a 51822805C my own is a 51804730D

both of them is bosch me 7.9.10

webmusta said:

my bad between 3-4 the light blinknig

Click to expand...

That might be the way it's designed to work... on, off, on, off:


You can also test the other O2 sensor, check if that behaves the same, move the sensors around see if the error moves...put the bulb on that see what it does...etc etc


Stupid (but relevant) question: are you sure you're testing the right sensor?
Are you using MES?

aurick86 said:

That might be the way it's designed to work... on, off, on, off:

You can also test the other O2 sensor, ...

Click to expand...

Looks like they use Pulse Width Modulation to control the voltage in the heater stage, but I doubt one would detect any "blinking" due to the high frequency used in PWM circuitry.

Be aware that even though they are the same, the two O2 sensors CANNOT be swapped (according to eLearn and other sources) ... I think it is due to their initial location, upstream or downstream the CAT, so the way they already "worn". Make sense since the downstream one kinda 'controls' the other.

BRs, Bernie

If someone here helped You fix -or better, understand- your issue, hit the thanks icon @ bottom right corner, it's free and makes us feel helpy ;-)

The only clear difference is the length of the wires.
Sensors are identical..... if they do differ in any way it will be in response time, frequency..etc something the the manufacturer decides.

In Any case should be good enough for troubleshooting.
When that is done, YES get the right parts.

so what im doing now do i need a new ecu. the o2 sensor i new from bosch

ECU's are pretty hard to kill, they have fuses and over-current protection.

I'd still suspect the sensor (even if it's new) or wires.
Replacing the ECU might not be plug-n-play...and even then it might not solve the problem.

Again: Are you sure the fault is for this O2 sensor? and not for the other one? after the cat?

aurick86

my problem is the o2 sensor not get heatet up and its the both sensor before and after the cat. so when i look for the o2 value its stays on 0.465 and wont regulate.
so the problem is on the heater circuit

O2 sensors will read 0.45v for about 2-3 minutes after a cold start...only after the car heats up enough it will go into closed loop mode then the O2 values will oscillate.

What are you using for interfacing to the ecu?? how did you read the errors?

I'm only trying to help you solve the problem and save you money. If you're sure the ECU is at fault, buy it. Then let me know how it goes.

aurick86 thansk for your time. i have try with bosch esi. wurth wow.
yes i know the close loop and open loop.
but like i said the o2 sensors does not heat up. do you know what the resistance should be on the o2 sensor for fiat.

p code p0135