# 2015 fiat 500 0% trim downstream O2 sensor



## 110year_old_fixer (Feb 7, 2021)

So here is what’s going on. 2015 fiat 500 sport with apx 94500 miles bought used two months ago. 


When I first got this car, I took it right to get serviced oil, plugs, and air filter. After leaving the shop about 20 miles away check engine light came on. Found out that the vacuum pump blew the seal and coated the O2 sensor with oil shorting them out. I took it to a fiat dealer to have the issue fixed. They changed both O2 sensors, vacuum pump seal and did a computer update, a total of $1200. Two weeks after getting the car fixed, the light came back on again. I have the OBD ran and came back with too lean, low voltage, and heater malfunction on the downstream season. I checked around the vacuum pump and found it leaking yet again. Upon doing some googling, it’s a known issue that when the vacuum pump seal goes, you have to replace the vacuum pump because it went bad. I went back to the dealer to have it fixed, not under warranty because the O2 sensor failed due to oil getting into it, and the pump wasn’t changed, so it had no warranty. I hate getting bent over like that. 

So I’ve taken it upon myself to fix the issue. 

I have ordered and replaced the vacuum pump and seal with the downstream O2 sensor—super simple job. But the only issue I’m having is the check engine light keeps coming back after being cleared. When I plug in the OBD2 and look at live data on the downstream sensor, I’m getting 0% trim. Brand new right out of the box. What is causing this? Btw the other readings are normal besides that one


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## raylo32 (Nov 25, 2006)

Maybe the connector is bad or the wire harness for that sensor is broken or shorted out? Could have happened with all the recent manipulation. And BTW, I am glad I don't have one of those cars! Not sure what the APX and vacuum pump do but it sounds like a mess.



110year_old_fixer said:


> So here is what’s going on. 2015 fiat 500 sport with apx 94500 miles bought used two months ago.
> 
> I have ordered and replaced the vacuum pump and seal with the downstream O2 sensor—super simple job. But the only issue I’m having is the check engine light keeps coming back after being cleared. When I plug in the OBD2 and look at live data on the downstream sensor, I’m getting 0% trim. Brand new right out of the box. What is causing this? Btw the other readings are normal besides that one


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## 110year_old_fixer (Feb 7, 2021)

The car has a very small engine as you can imagine so it doesn’t create enough vacuum for all the functions. The full name of the vacuum pump is brake booster vacuum pump.
How would I go about checking the wiring harness for a issue? I did get some electrical cleaner and cleaned the harness. But I’m not sure how to check with a multi meter if it’s working right or not.


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## raylo32 (Nov 25, 2006)

You'd have to trace the wires (or find the service manual schematic and location) then use a multimeter ohms resistance function (or a circuit testing light) to test them one by one for continuity from the connector contact to the other end, wherever that is. Or maybe at an intermediate junction connector if there is one. Be sure to disconnect the battery before doing any of this.



110year_old_fixer said:


> The car has a very small engine as you can imagine so it doesn’t create enough vacuum for all the functions. The full name of the vacuum pump is brake booster vacuum pump.
> How would I go about checking the wiring harness for a issue? I did get some electrical cleaner and cleaned the harness. But I’m not sure how to check with a multi meter if it’s working right or not.


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## Wrenrex (Feb 9, 2021)

Try disconnecting both battery cables and touch them together for about 10 seconds to reset the ECM. Then drive the car and see if the light comes back. You need to put some miles on the car after clearing the computer for fuel trim to be read. It'll always be zero right after a reset.


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## raylo32 (Nov 25, 2006)

It's not just that the light is on and that the ECM needs to relearn... he is reading the live data and that sensor is not online.



Wrenrex said:


> Try disconnecting both battery cables and touch them together for about 10 seconds to reset the ECM. Then drive the car and see if the light comes back. You need to put some miles on the car after clearing the computer for fuel trim to be read. It'll always be zero right after a reset.


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## 110year_old_fixer (Feb 7, 2021)

raylo32 said:


> You'd have to trace the wires (or find the service manual schematic and location) then use a multimeter ohms resistance function (or a circuit testing light) to test them one by one for continuity from the connector contact to the other end, wherever that is. Or maybe at an intermediate junction connector if there is one. Be sure to disconnect the battery before doing any of this.


I have found a video on how to test the car side harness and I’m getting 0 volts. I tested every port with the key on and the most I got was -0. I sprayed some electrical cleaner on the connector hoping that the it is just gummed up. I have let it set over night to let it dry and going to test it here soon.


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## 110year_old_fixer (Feb 7, 2021)

Wrenrex said:


> Try disconnecting both battery cables and touch them together for about 10 seconds to reset the ECM. Then drive the car and see if the light comes back. You need to put some miles on the car after clearing the computer for fuel trim to be read. It'll always be zero right after a reset.


I’ve put over 300 miles on since I’ve changed the sensor and rested.


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## Brainbucket (Mar 30, 2015)

The upstream O2 comes on faster than the down stream O2. Both have heaters to help with them coming on line faster. You don't look at the % but voltage. They generally start at .450 volts. When they get warmed up, then they start fluctuating. They only produce about 1 volt. So it should go to .880 volts to 200 volts. It does this very quickly. The upstream O2 is for the engine, the down stream O2 is there to protect the cat only. It shouldn't fluctuate as quickly as the upstream. Basically a flat line at around .450 volts but it does move. If it moves as fast as the upstream, you have a bad cat.


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## 110year_old_fixer (Feb 7, 2021)

Brainbucket said:


> The upstream O2 comes on faster than the down stream O2. Both have heaters to help with them coming on line faster. You don't look at the % but voltage. They generally start at .450 volts. When they get warmed up, then they start fluctuating. They only produce about 1 volt. So it should go to .880 volts to 200 volts. It does this very quickly. The upstream O2 is for the engine, the down stream O2 is there to protect the cat only. It shouldn't fluctuate as quickly as the upstream. Basically a flat line at around .450 volts but it does move. If it moves as fast as the upstream, you have a bad cat.


All of those reading look good, I just can’t get the engine light to go off. I turn it off comes right back on within a few miles for the same code. I found no shorts or anything. All my diagnostics come back perfect just can’t get the code to clear and Im also not seeing a fuel trim on a 50 mile trip or after putting 500 miles on.


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## raylo32 (Nov 25, 2006)

I guess it could also be the car's ECM failing. Rare, but I suppose it does happen.



110year_old_fixer said:


> All of those reading look good, I just can’t get the engine light to go off. I turn it off comes right back on within a few miles for the same code. I found no shorts or anything. All my diagnostics come back perfect just can’t get the code to clear and Im also not seeing a fuel trim on a 50 mile trip or after putting 500 miles on.


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## 110year_old_fixer (Feb 7, 2021)

raylo32 said:


> I guess it could also be the car's ECM failing. Rare, but I suppose it does happen.


I hope not. One of those cost over $700. But the other odd thing that is happening, I switched my revers lights to LED nice and bright, but they only work when the car is turned to the on position but not when the car is started.


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## huesmann (Aug 18, 2011)

Did your LEDs include resistors?


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## 110year_old_fixer (Feb 7, 2021)

huesmann said:


> Did your LEDs include resistors?


Nope


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## 110year_old_fixer (Feb 7, 2021)

So I just hooked my OBD2 scanner back in and looked at the Emissions test section and it is showing me that it is reading to hot. It’s showing the reading at 1329 Fahrenheit and the allowed max is 1046 Fahrenheit. Does this help narrow down the issue???


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## 110year_old_fixer (Feb 7, 2021)

Brainbucket said:


> The upstream O2 comes on faster than the down stream O2. Both have heaters to help with them coming on line faster. You don't look at the % but voltage. They generally start at .450 volts. When they get warmed up, then they start fluctuating. They only produce about 1 volt. So it should go to .880 volts to 200 volts. It does this very quickly. The upstream O2 is for the engine, the down stream O2 is there to protect the cat only. It shouldn't fluctuate as quickly as the upstream. Basically a flat line at around .450 volts but it does move. If it moves as fast as the upstream, you have a bad cat.


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## 110year_old_fixer (Feb 7, 2021)

Attached here is the most current OBD2 reading after I’ve cleared the code. This will be 2 posts.


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## 110year_old_fixer (Feb 7, 2021)

Post 2


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## Joeywhat (Apr 18, 2020)

Heated O2 sensors often require the PCM or similar module controlling the sensors to go through a relearn process. I would assume the dealer would have done this, but they might not have. Otherwise it could also be an incorrect O2 sensor installed.

If they replaced the O2 sensors they should fix this on their dime, as it's their screw up.


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## 110year_old_fixer (Feb 7, 2021)

Joeywhat said:


> Heated O2 sensors often require the PCM or similar module controlling the sensors to go through a relearn process. I would assume the dealer would have done this, but they might not have. Otherwise it could also be an incorrect O2 sensor installed.
> 
> If they replaced the O2 sensors they should fix this on their dime, as it's their screw up.


The first time the dealer replaced the vacuum pump seal that was leaking oil on to the O2 sensors they also replaced both O2 sensors. While the seal and sensors are under warranty the warranty only covers defective parts. Come to find out replacing the vacuum pump seal never fixes the issue. The vacuum pump has to to be fix because that is the real issue. So the vacuum pump started to leak again but I go to it early and it only started dripping oil onto sensor 2. Because of that it is not covered under warranty. I am more than 1000% sure the dealer knew this and knew I would be back to have the shaft me yet again. Screw me once shame on you screw me twice shame on me. Im not giving the dealer the opportunity to shaft me for another 1200 bucks.


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## Joeywhat (Apr 18, 2020)

Well, unless you have the necessary scan tool, the dealer will have to do that relearn process. And independent shop might also be able to.


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## 110year_old_fixer (Feb 7, 2021)

Joeywhat said:


> Well, unless you have the necessary scan tool, the dealer will have to do that relearn process. And independent shop might also be able to.


Relearn? I can’t find anything about that with my car. Everything I find just says it needs to go though a couple drive cycles.


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## Joeywhat (Apr 18, 2020)

110year_old_fixer said:


> Relearn? I can’t find anything about that with my car. Everything I find just says it needs to go though a couple drive cycles.


I don't know the specific process for your specific car, but for most heated O2 sensors, a relearn process of some sort must happen. The engine computer may be able to do that on its own, but would likely require a reset (either via the scanner you have, if it's able, or by disconnecting the battery for about 10 minutes).

Try either disconnecting the battery for a bit or looking if your scanner has an ECU reset button on it. It's different than just clearing codes.


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## Brainbucket (Mar 30, 2015)

Year, Make, Module, Engine size, and code please and I will look this up. But sounds like you have a vacuum leak at the vacuum pump.


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## 110year_old_fixer (Feb 7, 2021)

Brainbucket said:


> Year, Make, Module, Engine size, and code please and I will look this up. But sounds like you have a vacuum leak at the vacuum pump.


2015 Fiat 500 Sport 1.4L MultiAir P0141


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## 110year_old_fixer (Feb 7, 2021)

110year_old_fixer said:


> 2015 Fiat 500 Sport 1.4L MultiAir P0141


I have no misfires no hard idle MPG is on point until the code get tripped and no lose of power until the code is tripped. Once I clear the code MPG comes back and power comes back.


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## Brainbucket (Mar 30, 2015)

Verify that there is good pin to terminal contact in the O2 Sensor 1/2 and Powertrain Control Module connectors. If no problems are found, replace the O2 Sensor. When a new sensor is installed, a self-learn procedure should be completed. To do this, start the vehicle and allow it to idle for 30 seconds. Next, turn off the engine and let vehicle sit for 6 hours minimum where the temperature is between 0°C and 50°C (32°F and 122°F) ambient temperature. After the vehicle has sat, turn the key to the “Run” position for 10 seconds - DO NOT CRANK THE ENGINE. The learn is now complete and the vehicle can be started.


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## 110year_old_fixer (Feb 7, 2021)

Brainbucket said:


> Verify that there is good pin to terminal contact in the O2 Sensor 1/2 and Powertrain Control Module connectors. If no problems are found, replace the O2 Sensor. When a new sensor is installed, a self-learn procedure should be completed. To do this, start the vehicle and allow it to idle for 30 seconds. Next, turn off the engine and let vehicle sit for 6 hours minimum where the temperature is between 0°C and 50°C (32°F and 122°F) ambient temperature. After the vehicle has sat, turn the key to the “Run” position for 10 seconds - DO NOT CRANK THE ENGINE. The learn is now complete and the vehicle can be started.


I didn’t do that relearning process. Maybe when I get home today I’ll unplug the sensor plug it back in and do the relearning. Fingers crossed 🤞🏻 Thanks for your help. By the way where do you find that information? I’ve been trying to find the relearning but couldn’t.


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## Brainbucket (Mar 30, 2015)

I pay for ProDemand Automotive Repair and Identafix. Both are Automotive repair web sites that are for the professionals.


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## 110year_old_fixer (Feb 7, 2021)

Brainbucket said:


> I pay for ProDemand Automotive Repair and Identafix. Both are Automotive repair web sites that are for the professionals.


Oh very nice.


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## 110year_old_fixer (Feb 7, 2021)

Brainbucket said:


> I pay for ProDemand Automotive Repair and Identafix. Both are Automotive repair web sites that are for the professionals.


Ok so when I measured the resistance of the (F344) Fused ASD Relay Output circuit between the ASD Relay Output terminal and the O2 Sensor 1/2 harness connector I got a reading of 6.32 kilo-ohm.
Is the resistance below 0.5 Ohms 
No
Repair the (F344) Fused ASD Relay Output circuit for an open circuit or short to ground 

how do you do that??


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## raylo32 (Nov 25, 2006)

To eliminate the connector itself as an issue I'd stick a probe in the wire just upstream from it and test that again for ohms to the connector terminal. If that checks out OK then you need to trace that wire between the relay output and the sensor and find the break and splice the wire. If that isn't possible cut the old one off at the relay and and connector ends and abandon it. Run a new piece of wire and solder it up.



110year_old_fixer said:


> Ok so when I measured the resistance of the (F344) Fused ASD Relay Output circuit between the ASD Relay Output terminal and the O2 Sensor 1/2 harness connector I got a reading of 6.32 kilo-ohm.
> Is the resistance below 0.5 Ohms
> No
> Repair the (F344) Fused ASD Relay Output circuit for an open circuit or short to ground
> ...


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## 110year_old_fixer (Feb 7, 2021)

raylo32 said:


> To eliminate the connector itself as an issue I'd stick a probe in the wire just upstream from it and test that again for ohms to the connector terminal. If that checks out OK then you need to trace that wire between the relay output and the sensor and find the break and splice the wire. If that isn't possible cut the old one off at the relay and and connector ends and abandon it. Run a new piece of wire and solder it up.


I know it’s on the connector that would have been nice. I tested the car side connector back to the ECU C1 connector pin and tested resistance there that was good. Then I tested from the connector back to the ASD pin (yes my O2 sensor is connected to my ASD) and that when I got the crazy reading. I was also getting voltage in that line.

Hunting down a short in a car’s electrical is not in my wheel house of abilities. I’m not 100% sure of a good starting place. I’m not even sure have to search for a YouTube video for an example for my car. But taking the car to the shop would brake my bank so doing it myself is a must.


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## raylo32 (Nov 25, 2006)

Voltage??? I would do this kind of testing with the battery disconnected. But if you are indeed getting voltage in a line that isn't supposed to have any (unless it is for an O2 sensor heater?) then you may have 2 compromised wires... maybe even shorted together. Man, all I can say is good luck. This one could be a real bear to figure out.


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## Brainbucket (Mar 30, 2015)

Your PCM Needs to be reflashed.
TSB 18-024-18
SYMPTOM/CONDITION:

Customers may experience a Malfunction Indicator Lamp (MIL) illumination. Upon further

investigation the technician may find one or more of the following Diagnostic Trouble Codes (DTCs):
• *P1D7F00 ETC SelfLearning Failure.*
• P0141-00 - Oxygen Sensor 1/2 Heater Performance.
• Improved reverse lamp activation time.
• Cranks fast, as if no compression.
• P1524-00 - Oil Pressure Out Of Range - Camshaft Advance/Retard Disabled (2014 Vehicles
only).
• P1128-00 - Closed Loop Fueling Not Achieved - Bank 1 Upstream (2014 Vehicles only).
• P1046-00 - Cylinder 1 Oil Supply Solenoid Valve Overcurrent.
• P1048-00 - Cylinder 2 Oil Supply Solenoid Valve Overcurrent.
• P104A-00 - Cylinder 3 Oil Supply Solenoid Valve Overcurrent.
• P104C-00 - Cylinder 4 Oil Supply Solenoid Valve Overcurrent.
• P061A-00 Internal Control Module Torque Performance (2014 Vehicles only).
• Improved cold weather starting, below -20 °C (-4 °F).
The following powertrain system improvement/enhancement has been released to improve the

accuracy of Mode 6 data parameters in generic scan tools.
DIAGNOSIS:

Using a Scan Tool (wiTECH) with the appropriate Diagnostic Procedures available in

TechCONNECT, verify all related systems are functioning as designed. If DTCs or symptom

conditions, other than the ones listed above are present, record the issues on the repair order and

repair as necessary before proceeding further with this bulletin.

If the customer describes the symptom/condition listed above or if the technician finds the DTC,

perform the Repair Procedure.

REPAIR PROCEDURE:

NOTE: Install a battery charger to ensure battery voltage does not drop below 13.2 volts. Do
not allow the charging voltage to climb above 13.5 volts during the flash process.
NOTE: If this flash process is interrupted/aborted, the flash should be restarted.
1. Reprogram the PCM with the latest software. Detailed instructions for flashing control modules
using the wiTECH Diagnostic Application are available by selecting the application’s “HELP”
tab.
NOTE: Follow all screen prompts that apply to the vehicle.
2. Is the vehicle equipped with a manual transmission?
• YES >>> Fully depress the clutch pedal and then release it. Press “OK” to continue.
• NO >>> Press “OK” to continue.
3. Is the vehicle equipped with cruise control?
• YES >>> Depress cruise on/off switch until the cruise indicator in the cluster illuminates and
press “OK” to continue.
• NO >>> Press “OK” to continue.
4. Clear any DTCs that may have been set in all modules due to reprogramming. The wiTECH
application will automatically present all DTCs after the flash and allow them to be cleared.
18-024-18 
Looks like dealer.


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## 110year_old_fixer (Feb 7, 2021)

Brainbucket said:


> Your PCM Needs to be reflashed.
> TSB 18-024-18
> SYMPTOM/CONDITION:
> 
> ...


I do not have a wiTECh so I won’t be able to flash my own PCM.
But I did however go back and investigate an area on the wiring I thought might be an issue. I thought originally the wire was just a bit dirty (with my not so perfect eye site). So I took a photo of the wires so I could zoom in and this is what I found. Sadly the break in the wire is so close to the connector I wont be able to mend them back together. I’ve been looking to just a replacement O2 harness connector but no luck. It seems I’d I want to fix this issue in full I’ll need to replace the C1 PCM harness connector all together. I found one at a junk yard for 300 after it ships to me it’s the same price as a new one, a bit over 400. A bit outside of my price range at the moment.


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## 110year_old_fixer (Feb 7, 2021)

110year_old_fixer said:


> I do not have a wiTECh so I won’t be able to flash my own PCM.
> But I did however go back and investigate an area on the wiring I thought might be an issue. I thought originally the wire was just a bit dirty (with my not so perfect eye site). So I took a photo of the wires so I could zoom in and this is what I found. Sadly the break in the wire is so close to the connector I wont be able to mend them back together. I’ve been looking to just a replacement O2 harness connector but no luck. It seems I’d I want to fix this issue in full I’ll need to replace the C1 PCM harness connector all together. I found one at a junk yard for 300 after it ships to me it’s the same price as a new one, a bit over 400. A bit outside of my price range at the moment.


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## Brainbucket (Mar 30, 2015)

You can just take out the retainer and pull the pin out using something to push down on the clip inside the connector. Solder it and put in back in the connector, I do it all the time.


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## 110year_old_fixer (Feb 7, 2021)

Brainbucket said:


> You can just take out the retainer and pull the pin out using something to push down on the clip inside the connector. Solder it and put in back in the connector, I do it all the time.


Could you make a video on how to do it? I’ve never taken one apart.


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## raylo32 (Nov 25, 2006)

If it is a Molex connector you just need one of these. You just push it in from the open side and the pin should come out the back. These connectors have little spring ears that pop up to hold the pin in place and the tool presses them flat to release them. As BB says, solder the wire up to the pin and snap it back in. If you need to extend the wire first to account for removing the bad part just solder splice a piece in and do it up with shrink tube.

Amazon.com: Male/Female 4 Pin Molex Power Connector Pin Remover Computer Wire Extractor Tool for Modding/Wiring/Sleeving (for .062" and 0.093" pins) : Electronics


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