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My First Check Engine Light (P0156)

2K views 38 replies 7 participants last post by  1997ThunderbirdLXV6 
#1 ·
I guess it had to happen at some point...ugh.

Next steps? There are no drivability issues at this time.

 
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#6 ·
Well; I'd bet the 25 year old o2 sensors have finally given up. The post-cat sensors are used too. I usually swap the primaries to the secondaries, and put new ones on for primaries. You can clear codes by pulling fuse 15 under the hood, and trying to start the car.put the fuse back in, and start the car. Do the drive sequence, and see if it sets the code again.
 
#8 ·
With your reader, it looks like there is an "erase" button to delete codes. Always do that versus disconnecting the battery, which can leave you with some quirky drivability until everything relearns.

Al
 
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#10 ·
I just use my xcal2. :)
 
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#17 ·
Check Engine Light came back today. I just got back from a road trip, so it's been about 1,000 miles since the Light first appeared (and disappeared after I disconnected the battery).

It's the same code (P0156), and again it showed "(1/2)" after the code. I asked the guy if that meant that there were two codes total, but he appeared a bit clueless. I need to invest in my own code reader.

As before, there are no drivability issues at all (which I'm guessing is because this sensor collects information about catalytic convertor performance only, but doesn't actively influence fuel trim).
 
#19 ·
That usually means the sensor is shorted. Buy a set for the front, and swap the current fronts to the rear. While you're there, make sure the wires aren't touching the exhaust.
 
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#20 ·
Just from looks, does this appear to be the factory original sensor?

(Side note: that rusty shift mechanism doesn't look very confidence inspiring either.)




Buy a set for the front, and swap the current fronts to the rear.
Oh my...I need to keep this simple!

Are fronts and backs the same part? On Rockauto, some brands seem to differentiate between upstream and downstream while others don't.
 
#23 ·
An oxygen sensor socket will make changing them out easier. Most parts stores will sell or even rent out the whole kit that usually come with 3 different styles. The ones on my Cougar came out easily enough, but it's still a good practice to spray them with PB blaster and let it sit for a few hours or even overnight.

IMO either just replace the one that's bad to save yourself time and money, or go all out and replace all 4.
 
#25 ·
Finally I got a little Bluetooth scanner. I used the Car Scanner app, and I'm wondering if it's poorly designed: when I look up active codes, it explains P0156 as sensor 1, not sensor 2 :unsure:.

Meanwhile, I obtained this live data screen shot. Anyone can interpret this for me?

I guess my biggest question is: why does it trigger a code for the sensor, not for the catalytic converter?

 
#27 ·
No, that ******* sensor is bad, lol. Replace the
o2S2 sensor first. the others aren't pretty, but they are at least switching. O2s2 is not.
 
#28 ·
The exaust heat keeps the front ones relatively clean, but crap settles on the rear ones. our cars cycle a lot of oil thru the pcv and egr, so they get dirty. That's why I swap them every 100k, ang move the front ones to the back. If you want them to last, get the ntk sensors.
 
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#30 ·
The one on the left is not working at all. The one on the right is barely working. Standard sensors switch from rich to lean, the more switches the better. Left is not switching, right is late and weak. Again; replace the fronts, move the fronts to the rear, and this all goes away.
 
#35 ·
replace the fronts, move the fronts to the rear, and this all goes away.
Do you know which wire lengths I need for the V6? It seems these sensors come with different lengths wires (?).
From what I saw the other day, 1/bank 1 had a long harness with a connector all the way forward of the engine block; the others were fairly short. But I didn't measure...
 
#32 ·
iirc, that looks like a bosch sensor. Thats the problem.
 
#33 ·
Funny side note: several weeks ago I posted about a rattle when in gear at a standstill.

Turns out, the connector of this O2 sensor 2/bank 2 was touching the body. The connector is attached to the transmission with a Christmas tree fastener, but there isn't sufficient clearance; as a result transmission vibration was transferred to the body right next to the driver's feet.

I'm wondering if that caused some problems for this sensor. I used a zip tie to hold the connector away from the body; rattle is gone.

Haven't changed the sensor yet, but that'll come soon. Just need to budget for parts plus the appropriate tool.
 
#34 ·
Monitoring the two downstream sensors, what's interesting is that when they are cold, bank 1 reads 0 volts while bank 2 (the problem sensor) reads 1.28 volts.

Once they warm up, their readings are mostly similar.

Here is a short drive today, with an interruption in the middle where I went shopping.

 
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