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Discussion Starter #1
Hello Everyone,

This is my first time entering into any type of forum online. I need your help. I own a 2015 Fiat 500c Pop convertible. Bought it 3 months ago. Great car. Only problem
is, the check engine light came on shortly after I bought it. I bought an OBD-2 reader and found out the code is P0141: heater malfunction on the downstream O2 sensor.
No big deal. I replaced both the upstream and downstream O2 sensors with BOSCH purchased from Autozone. Great. everything was great. Until the check engine
light came on again. I cleared the code... and it popped back on next time I drove. I even did the recommended installation proceedure where you install the sensor, turn the engine
over for 30 seconds, let it sit for 6 hours, turn the key to accessories on for 10 seconds, then good to go. Not good to go though. It came back on. I was reading in the owners manual
that if the check engine light flashes after 10 seconds with the key in the accessories on position, it means the OBD-II system onboard is not ready. Can anybody shed light on
this situation? Thank you for reading my post and I look forward to any and all comments.

W.K.
 

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I'm not an expert, but was studying up on how these work this month. Welcome to the group and I hope this helps.

Yes, that error is for the heater circuit in the O2 sensor. The normal test is to put an Ohm meter across the sensor's heater circuit wires and see if a proper resistance reading is given. (There are multiple videos on youtube that discuss O2 sensor and heater circuit problems, but are generic.) Usually if the sensor heater is bad, it's because the element has broken, infinite resistance. If that isn't the case, then the error lies elsewhere in the system, or the new unit is also defective.

This is for O2 sensor 1, but the heater circuit test is the same.

As you know, the secondary O2 sensor verifies the cat-conv is functioning properly, but it can't do its job until it reaches operating temp, somewhere around 600 degrees. The heater is a filament inside that brings it to temp quicker, usually under a minute. Until it's reached operating temp, the sensor won't generate the desired .45V the computer wants to see.

I haven't verified this generic page's advice on the 500, but it sounds correct: https://www.700r4transmissionhq.com/p0141-fiat-500/

I'm not familiar with the check engine light flashing when left on for 10 seconds. The only mention on my '18 is, when running, if it flashes, it's an indication of a problem serious enough to cause damage... usually to the cat-conv.
 

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Discussion Starter #3
Map,

Thank you for the reply. I didn't want to, but I may have to buy a multi-meter. Either that, or borrow one. It surprises me because twice I have installed two new O2 sensors in the downstream slot. Maybe the upstream is the problem but I don't think so.

Thank you for the advice.

W. K. H.
 
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