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Old 14-03-2019   #1
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fiat grande punto 1.4 tjet o2 sensor problem

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
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Old 14-03-2019   #2
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Re: fiat grande punto 1.4 tjet o2 sensor problem

Forgive this BUT did you clear the original fault code?
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Old 14-03-2019   #3
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Re: fiat grande punto 1.4 tjet o2 sensor problem

yes i have.
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Old 14-03-2019   #4
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Re: fiat grande punto 1.4 tjet o2 sensor problem

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
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Last edited by webmusta; 14-03-2019 at 16:14.
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Old 15-03-2019   #5
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Re: fiat grande punto 1.4 tjet o2 sensor problem

Quote Originally Posted by webmusta View Post
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
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
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Last edited by Bernievarian; 15-03-2019 at 08:36.
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Old 15-03-2019   #6
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Re: fiat grande punto 1.4 tjet o2 sensor problem

Quote Originally Posted by webmusta View Post
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
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-gra...e-box-diagram/
https://www.autogenius.info/fiat-bra...e-box-diagram/

Engine and ECU is the same from the bravo... so fuses might be similar as well.
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Last edited by aurick86; 15-03-2019 at 10:26.
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Old 16-03-2019   #7
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Re: fiat grande punto 1.4 tjet o2 sensor problem

i use the o2 sensor for load
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Old 16-03-2019   #8
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Re: fiat grande punto 1.4 tjet o2 sensor problem

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

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Old 16-03-2019   #9
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Re: fiat grande punto 1.4 tjet o2 sensor problem

Quote Originally Posted by Bernievarian View Post
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 ;-)
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
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Old 19-03-2019   #10
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Re: fiat grande punto 1.4 tjet o2 sensor problem

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
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Old 19-03-2019   #11
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Re: fiat grande punto 1.4 tjet o2 sensor problem

my bad between 3-4 the light blinknig
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Old 19-03-2019   #12
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Re: fiat grande punto 1.4 tjet o2 sensor problem

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

both of them is bosch me 7.9.10
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Old 20-03-2019   #13
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Re: fiat grande punto 1.4 tjet o2 sensor problem

Quote Originally Posted by webmusta View Post
my bad between 3-4 the light blinknig
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?
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Last edited by aurick86; 20-03-2019 at 09:47.
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Old 20-03-2019   #14
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Re: fiat grande punto 1.4 tjet o2 sensor problem

Quote Originally Posted by aurick86 View Post
That might be the way it's designed to work... on, off, on, off:

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

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Old 20-03-2019   #15
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Re: fiat grande punto 1.4 tjet o2 sensor problem

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.
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