Check engine light is on.
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Junior User
Joined: Mar 2020
Posts: 57
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Check engine light is on.
96 f-150 was running fine since I purchased, but this morning the check engine light came on. I ordered an odb2 reader on Amazon, and it arrived four hours later !
getting three codes - P0171 - system too lean ( bank 1)
P0174 - system too lean ( bank 2)
P0155 - O2 heater circuit ( bank 2, sensor 1)..
there are plenty of YouTube’s on how to diagnose these, but YouTube sent me down some rabbit holes when I recently did some brake work, hoping to again get some better direction here. Any suggestions where to start? Should i replace the o2 sensor? Thanks.
getting three codes - P0171 - system too lean ( bank 1)
P0174 - system too lean ( bank 2)
P0155 - O2 heater circuit ( bank 2, sensor 1)..
there are plenty of YouTube’s on how to diagnose these, but YouTube sent me down some rabbit holes when I recently did some brake work, hoping to again get some better direction here. Any suggestions where to start? Should i replace the o2 sensor? Thanks.
Logistics Pro
Joined: Aug 2014
Posts: 3,570
Likes: 854
Read carefully: "P0155 - O2 heater circuit ( bank 2, sensor 1).."
That is the 'heater circuit', not the O2 sensor. Replacing O2 sensor will not fix, do not replace.
You need to look for a short to ground, or open circuit.
Pulled this from another thread:
"Use a voltmeter to test if there is 13 volts heater source to heat the sensors.
Do not try to measure the"""OX"""" sensor resistance part of the OX detector but you can test for heater being open.
Likely a short to ground, or an open in the harness or plug to the sensor."
That is the 'heater circuit', not the O2 sensor. Replacing O2 sensor will not fix, do not replace.
You need to look for a short to ground, or open circuit.
Pulled this from another thread:
"Use a voltmeter to test if there is 13 volts heater source to heat the sensors.
Do not try to measure the"""OX"""" sensor resistance part of the OX detector but you can test for heater being open.
Likely a short to ground, or an open in the harness or plug to the sensor."
Thread Starter
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Junior User
Joined: Mar 2020
Posts: 57
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I don’t hear any vacuum leaks, but probably not the best way to test.
i need to find a good book which explains what the values should be, this is my first venture into the modern world, after spending last 30 years wrenching on jeep and boat motors with carbs and points! but it looks like the freeze frame from when I threw the p0171 says I was going 14 mph, and 1080 rpm,
bank1
stft = 19.5%,
ltft = 8.6% .
b2
stft = 16.4
ltft = 9.4,
When idling in my driveway, the live data is telling me these numbers, at 835 rpm.
bank1
stft = -16.4
ltft = 24.2
b2
stft = -16
ltft = 25
i need to find a good book which explains what the values should be, this is my first venture into the modern world, after spending last 30 years wrenching on jeep and boat motors with carbs and points! but it looks like the freeze frame from when I threw the p0171 says I was going 14 mph, and 1080 rpm,
bank1
stft = 19.5%,
ltft = 8.6% .
b2
stft = 16.4
ltft = 9.4,
When idling in my driveway, the live data is telling me these numbers, at 835 rpm.
bank1
stft = -16.4
ltft = 24.2
b2
stft = -16
ltft = 25
Last edited by Old green123; May 1, 2020 at 03:40 PM. Reason: Misspell
Hotshot
Joined: Jun 2015
Posts: 12,879
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[QUOTE=wwhite;19258068]Read carefully: "P0155 - O2 heater circuit ( bank 2, sensor 1).."
That is the 'heater circuit', not the O2 sensor. Replacing O2 sensor will not fix, do not replace.QUOTE]
I disagree. The heater is in the sensor. It could still be the sensor has failed.
That is the 'heater circuit', not the O2 sensor. Replacing O2 sensor will not fix, do not replace.QUOTE]
I disagree. The heater is in the sensor. It could still be the sensor has failed.
Logistics Pro
Joined: Aug 2014
Posts: 3,570
Likes: 854
I'm going with the simple fact that most electrical problems are poor connections, just unplug, inspect, clean and plug back in.
Senior User
Joined: Feb 2010
Posts: 180
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Check for vacuum leaks. You won't necessarily hear them. After a tune up this weekend I got a CEL. Discovered I had accidentally knocked a vacuum line loose on passenger side. Plugged it back in. No more CEL. Easiest thing to do first.
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Junior User
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I think the sensor may be acting up. Now it won’t jump back into ‘closed loop’ even after driving around for a while. So not sure if the live data numbers mean that much?
can anyone one tell me which side is bank 1, and which is bank 2? The drivers side o2 sensor has all the room in the world to get a wrench on it. Passenger side looks like a real pita. I bought a cd with the service manual, of course I don’t have any working computers left with a cd drive , at least none I remember the password for.
can anyone one tell me which side is bank 1, and which is bank 2? The drivers side o2 sensor has all the room in the world to get a wrench on it. Passenger side looks like a real pita. I bought a cd with the service manual, of course I don’t have any working computers left with a cd drive , at least none I remember the password for.
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