Check engine light came on and got 2 codes....

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and I dont know what they mean P1131 Lack Of HO2S11 Switch - Sensor Indicates Lean P1151 Lack Of HO2S21 Switch - Sensor Indicates Lean nice forum BTW ;\)
 
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do you have a k&n or similar filter on this vehicle. basically both front O2's indicate lean. on Ford's this usually points to the MAF being bad, which usually go bad from overoiling an air filter.
 
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P1131 Upstream Oxygen Sensor for BANK 1 is staying lean P1151 Upstream Oxygen Sensor for BANK 1 is staying lean H02: S1: 1: HO2: (Heated Oxygen sensor) S1/2: bank 1/2 1/2: sensor 1/2 Sensor 1 is upstream sensor, BEFORE the catalytic converter. This is the sensor that the computer uses to adjust your air/fuel mixture Sensor 2 is downstream sensor, AFTER the catalytic converter, Monitors the catalytic converter performance ONLY. So, the codes indicate a problem with BOTH of the oxygen sensors that are before the catalytic converters...... So, these are between the motor and the catalytic converters. May or may not be close to the exhaust manifold, on of mine is easy to see, the other is up....harder to see. It seems that these codes differ from the P0171 and P0174 codes, which indicate close to the same thing (usually a vaccum leak) in that the 131/151 is indicating that the voltage is out of the acceptable range.....pointing to a problem with the sensors. Odd that both would fail at the same time though. Have you had any service done recently? Oh, just saw the message about K&N, try the cleaning the MAF (use NON-Residue Electronic cleaner). Remember that the codes will STAY, and the Check Engine Light will STAY on after the problem is solved......for a certain amount of time WITHOUT a failure. The codes are held for a while to enable one to troubleshoot a problem that comes and goes. So, unless you clear the codes, they will stay for a while after the problem is solved.
 
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FWIW, I recently checked codes for a neighbor on their 3.0L Ranger and received two similar codes. P0171 & P0174 (system to lean on both banks) The culprit we found was was a generic air filter that was sagging in the air box allowing air to bypass it.
 

DreamerGT

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So would It be possible that I need new o2 sensors? I have 107k miles on the car and still on the original sensors. And it came on when I was letting the car idle after flushing the coolant.
 
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After you perform the maintenance, whatever it is, remove the positive terminal from your battery and hold it to chassis ground for at least ten seconds to clear the data and codes. Or you can disconnect both terminals and hold them together for ten seconds. This allows the caps in the ECU to safely discharge at a quick rate instead of having to leave the battery disconnected for several hours. I've done it to both my Trooper and my XC70. It works like a champ. You'll have to drive the car for a little while for the ECU to re-learn the way you drive.
 
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If this is for your Crown Vic or Mustang, FORDs seem to not have a lot of oxygen sensor failures. The originals are rated for 100K miles, and should be good for longer. I changed my upstream sensors at about 160K miles, and it made no difference.....motor ran great before and after, no change in fuel economy. Usually oxygen sensor codes are for something else that is causing the code.....lean codes most commonly being caused by a vaccum leak (air leaking into the intake that the MAF does not get to measure). Having said this....having BOTH sensors fail at the same time is even less likely. I would clean the MAF, clear the codes, and see what happens. On my FORD, it took longer than mentioned to drain the charge when discharging the electrical system. What I have done is to have the headlights turned ON when I disconnect the battery terminal......5 minutes later, reconnect. HOWEVER, if you have a code reader, many of those have a function to clear the codes, and I would do that if yours does. In the UNLIKELY event that you need to replace the oxygen sensors, I would buy the Motorcraft brand. I also like to replace both of the upstream sensors together so that you have better matched switching charactoristics between the 2. I have read that the switching speed slows down as they age, which is why I changed mine, but it was not needed. The computer monitors the switching speed, and if they get too slow, it will light the CEL and set a code that specifically states that the switching speed is too slow. Downstream is not so important as they switch slower due to the monitoring that they are doing (and only serve to tell the computer that the catalytic converters are working).
 
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Sure, clean the MAF. But a leaky vacuum line, PCV system, or intake leak can also cause this. When 2 sensors go out at once, look for something that affects them both.
 
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I'd clean the MAF as said above with aNON residue contact cleaner. I'd then pull the O2's out and clean them with the same cleaner. Put some dielectric grease inside the connectors for the O2's when you put it back together. I mention this because I had my upstream O2's giving codes and it ended up being because of corrosion inside the connector causing voltages to read weird sometimes. The after cleaning them and putting some dielectric grease in the connectors it all went away. Also, one other tidbit i'll throw out here. If this is on your Mustang and you have MIL eliminators ont he rear O2's for a catless midpipe they might throw codes after driving in the rain. I had this problem and it was water getting into the connectors. The grease solved that problem also and has been fine for 50k miles now. As far as clearing the ECU, I've never held the pos to chassis ground. I always just disconnect the pos from the battery, leave it for about 10 minutes, then step on the brake pedal a few times and put the cable back on.
 
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