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dghardysr, Auto Mechanic
Category: Ford
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Experience:  Helping you help yourself with your automotive repairs
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2001 windstar: check engine light..engine light came..egr..fine until

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2001 windstar 3.8 check engine light came on a couple of months ago, scanned it and their wher a couple of codes i dont remember the numbers, i changed the egr, and all the 02 sensors. it has been fine until yesterday, iscanned it and it shows code p0156 02 sensor, could this have gone bad all ready, or should i look for something else?
Hello, and thanks for using Just Answer. My name is XXXXX XXXXX I will be helping you. The code P0156 indicates that the downstream oxygen sensor output voltage is not within calibrated limits. You may already know, but in case you don't, the down stream oxygen sensor is located furtherest away from the engine in the exhaust system, the upstream is located closest to the engine in the exhaust system. Some vehicles have 4 sensors, some 2, some only 1. I would replace the downstream oxygen sensor, it is possible it has gone bad. It is also possible to have a broken wire or a bad connection to the sensor. Most auto parts stores will warranty parts for a period of time. I would ask if it is still under warranty. I would think it would be if it is only a couple months old. Hope this helps. Thanks and have a great day.
dghardysr and 4 other Ford Specialists are ready to help you
Customer: replied 4 years ago.
replaced the 02 sensor again drove about 20 miles the light came on again, pulled the plug off and have power at the 2 white wires, any ideas?
Have you had the vehicle scanned after you replaced the sensor? If not, I would suggest having it scanned and find out what code it has. Then go from there.
Customer: replied 4 years ago.
its the same code po-156

Here are some test that you can do to try and figure out what is happening. Hope this helps.

80) DTC P0136, P0156, P1137, P1138, P1157 & P1158

Continuous Memory DTCs P0136 and P0156 indicate output voltage of downstream HO2S is not within calibrated limits. KOER DTCs P1137 or P1157 indicate PCM does not detect output of HO2S in a calibrated amount of time (lean condition). DTCs P1138 or P1158 indicate PCM does not detect output of HO2S in a calibrated amount of time (rich condition). DTCs P0136, P1137 and P1138 are for HO2S-12. DTCs P0156, P1157 and P1158 are for HO2S-22. Possible causes are:

  • Damaged Wiring Harness Or Connector
  • Crossed Sensor Wires
  • Exhaust System Leaks
  • Contaminated Or Faulty HO2S

DTCs P0136 and P0156 can be set when leaks exist in exhaust system between engine and rear of catalytic converter. Possible causes are:

  • Incorrect HO2S Torque
  • Exhaust System Leaks
  • Punctures Or Cracks In Pipes Leading To Or In Catalytic Converter

Inspect exhaust system including catalytic converter and HO2S. Repair as necessary.

Check HO2S Ground Circuit In PCM
Turn ignition switch to OFF position. Disconnect PCM connector(s). Using a DVOM, measure resistance between PCM harness connector PWR GND and SIG RTN terminals. If resistance measurement is 5 ohms or more, replace PCM.