Check Engine Light On

Asked by Mar 13, 2017 at 10:11 AM about the 2005 Ford Freestar S

Question type: Maintenance & Repair

My check engine light is on. The gas cap seal
appears to be intact. The diagnostics showed code
P2195: O2 sensor signal biased/stuck lean bank 1
sensor 1. My Master mechanic changed the O2
sensor and he changed the fuel pump and filter per
my request on this 178,000 mile vehicle. I drove to
test and prepare for annual inspection and
emissions test and the light came back on with
same code as above. It idles smooth and seems to
run well except for slight repeated hesitation in
power response at steady 50 mph. You can feel the
slight wavering of power at steady speed as a very
faint jerkiness. Any idea on next step since we
already changed the upstream O2 sensor?

2 Answers

110,665

Use a scan tool to get readings from the sensor, and monitor the short and long term fuel trim values and O2 sensor or Air Fuel Ratio sensor readings. Also, look at the freeze frame data to see the conditions at the time the code was set. That should help determine if the O2 AF sensor is operating correctly. Compare with manufacturers values. If you don’t have access to a scan tool, you could use a multimeter and back-probe the terminals on the O2 sensor wiring connector. Check for shorts to ground, short to power, open circuits, etc. Compare specs with manufacturers specifications. Visually inspect the wiring & connectors leading to the sensor, check for loose connectors, wires rubbed/chaffed, melted wires, etc. Repair as necessary. Visually inspect vacuum lines. You can also test for vacuum leaks using propane or carburetor cleaner along the hoses while the engine is running, if the RPMs change you likely found the leak. Be very careful if doing that, and have a fire extinguisher within reach in case something goes wrong. For example, on a bunch of Ford vehicles, the hose that goes from the PCV to the throttle body can melt causing P2195, P2197, P0171, and/or P0174 codes. If a vacuum leak is determined to be the problem, it would be prudent to replace all vacuum lines if they are getting older, becoming brittle, etc. Use a digital volt ohm meter (DVOM) to check other sensors mentioned such as MAF, IAT, for proper operation. Perform a fuel pressure test, verify readings against manufacturers specification. If you’re on a budget and you only have an engine with more than one bank and the problem is only with one bank, you could swap the sensor from one bank to the other, clear the code, and see if the code is followed to the other bank. That would tell you it is the sensor/heater itself that’s failed. Read more at: https://www.obd-codes.com/p2195 Copyright OBD-Codes.com

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