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Old 03-16-2009, 07:28 AM
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Ford code P1151 Lack of H02s21 Switches - Sensor Indicates Lean

Ford code P1151 Lack of H02s21 Switches - Sensor Indicates Lean
2002 Taurus with the 3.0L engine

Used car with ~ 33,000km (owned by a senior citizen before my sister bought it) So, car sat idle for long periods and only did short trips.

I'm not sure how to proceed with this code aside from simply replacing O2 sensors. Car runs fine, occasional rotten egg smell from exhaust. But the car has four oxygen sensors, and it's not telling me if it's the left or right bank.

Googling, I found these suggestions:

P1151 - Lack of H02S21 Switch - Sensor Indicates Lean

Fuel Injectors Malfunction
0xygen Sensor Failure
Exhaust Leak
EGR Failure
MAF Failure

So we'll start dumping fuel injector cleaner in the tank, and I'll spray clean the MAF. Aside from scanning the oxygen sensor readings (I can practically replace both pre-cat sensors for the price of a diagnostic with an advanced reader), any other suggestions for simple diagnostics?
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Old 03-16-2009, 10:06 AM
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Re: Ford code P1151 Lack of H02s21 Switches - Sensor Indicates Lean

Quote:
Originally Posted by Slowpoke View Post
Ford code P1151 Lack of H02s21 Switches - Sensor Indicates Lean
2002 Taurus with the 3.0L engine

Used car with ~ 33,000km (owned by a senior citizen before my sister bought it) So, car sat idle for long periods and only did short trips.

I'm not sure how to proceed with this code aside from simply replacing O2 sensors. Car runs fine, occasional rotten egg smell from exhaust. But the car has four oxygen sensors, and it's not telling me if it's the left or right bank.

Googling, I found these suggestions:

P1151 - Lack of H02S21 Switch - Sensor Indicates Lean

Fuel Injectors Malfunction
0xygen Sensor Failure
Exhaust Leak
EGR Failure
MAF Failure

So we'll start dumping fuel injector cleaner in the tank, and I'll spray clean the MAF. Aside from scanning the oxygen sensor readings (I can practically replace both pre-cat sensors for the price of a diagnostic with an advanced reader), any other suggestions for simple diagnostics?
When you get an O2 sensor code like this, the acroynm HO2S21 means:
Heated
O2 Sensor
Bank 2
Sensor 1

Bank 2 means the second bank of the engine (the side that DOES NOT have cylinder #1), and sensor 1 means the primary sensor. P1151 means the sensor is reporting lean, so an EGR could be stuck, you could have a vacuum leak, or perhaps a cracked exhaust manifold on that side. Could also be an incorrectly reporting MAF (although that should affect both sensors), or lastly a faulty O2 sensor.

If it was me I would start off searching for a vacuum leak, pull the heat shield and look for a cracked exhaust manifold, and then just check if bank 2 is the bank that has the EGR inlet on the exhaust manifold. If so, then I would have the EGR system checked next. If all else fails, then buy a new sensor.
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Old 03-16-2009, 10:11 AM
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Re: Ford code P1151 Lack of H02s21 Switches - Sensor Indicates Lean

Just saw that the car was owned by a senior and has very low kms... I would assume that the exhaust manifold isn't cracked as it wouldn't be rusted enough at this point in its life. I would lean more towards a fouled up EGR system or faulty O2 sensor, since the short drives and excessive idling can contribute to this.
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Old 04-03-2009, 06:52 PM
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Re: Ford code P1151 Lack of H02s21 Switches - Sensor Indicates Lean

MAF and Injector cleaner haven't worked. Looks like I might be ordering an O2 sensor. First I'll swap them to check if it's the sensor or the EGR.

Can anyone please tell me which is bank 2 on the 2002 Ford Taurus "U" code engine? I asked a Mississauga dealer service advisor, and first he told me the firewall side. Then he told me, "Nope... nope it would be the front of the car."

"You sure?"

Pause

"Great. Thanks."
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Old 04-11-2009, 10:12 PM
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Re: Ford code P1151 Lack of H02s21 Switches - Sensor Indicates Lean

Timely post. My Mustang just started throwing the same code.

Any progress Stephen?
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Old 04-13-2009, 05:00 PM
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Re: Ford code P1151 Lack of H02s21 Switches - Sensor Indicates Lean

A bit more detail on the code:
P1151 Lack of Upstream Heated Oxygen Sensor Switch -Sensor Indicates Lean -Bank 2
That would suggest the sensor before the converter closest to the radiator (or driver side on the Mustang).
Doesn't mean changing the sensor will fix the problem!!!
Hope that helps.
Perry
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Old 04-13-2009, 05:08 PM
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Re: Ford code P1151 Lack of H02s21 Switches - Sensor Indicates Lean

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Originally Posted by G-ForceJunkie View Post
Any progress Stephen?
No, I've been waiting for warmer weather. I did have this idea though... there doesn't appear to be a separate part number for bank 1 / bank 2 oxygen sensors. So, although it may end up being more trouble than it's worth, I thought of SWAPPING the bank 1 / bank 2 O2 sensors. If the code changes banks, I know it's the sensor. If it doesn't, I know that's not the problem.

It's my sister's car and she's a student, so some skinned knuckles are preferable to spending money on sensors that aren't needed.

Here's a question... can you use Kleen Flo sensor cleaner on an O2 sensor with a tooth brush? I've never tried this with any of my cars before, I've always just replaced them. But, as mentioned, Sis has no money...
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Old 04-27-2009, 11:32 PM
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Re: Ford code P1151 Lack of H02s21 Switches - Sensor Indicates Lean

Turned out to be O2 related for me. Can't say for sure that it was the O2, but it was either the O2 sensor, or the O2 wiring harness.
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