RepairPal is your advocate for car care advice and guidance

Q: keep getting codes 0172 and 0175,before this o2 sensor bank 2 kept going on on 1997 Mercury Cougar

o2 sensor was going on first for about 2 years now have changed sensor,plugs,wires runs fine just dont know what else keeps switching codes around help need answers smog check soon.By the way my 4.6 averages about 32-35 highway mpg. email me at .
Get a Repair Estimate
Guaranteed by certified locations nationwide. Learn more
RepairPal estimates are guaranteed at over 1,700 quality certified locations nationwide. Learn more
Vehicle Application: 1997 Mercury Cougar XR-7 4.6L, Vin W, Eng Cfg V8 1999 Ford F-350 Super Duty 6.8L, GAS, Vin S, Eng Cfg V10

Customer Concern: The Malfunction Indicator Lamp (MIL) is on with codes P0172 and P0175 in memory. The long-term fuel trim readings at idle are around negative 20%. The Barometric Pressure (BARO) reading on the scan data is 144 Hz. The shop's elevation is about 500 feet above sea level.
Tests/Procedures: 1. Clean or replace the Mass Airflow (MAF) sensor. To clean the MAF sensor, carefully remove the plastic sensor from the aluminum housing, and spray the sensing elements, at the tip of the sensor, with electrical contact cleaner, or a good brake cleaner. Do not use any cleaner that will leave a residue. Check the sensor passage in the housing for any debris, and if the housing inlet has a screen, make sure it is also clear of debris. Let the sensor air dry, then carefully reinstall it in the housing.

2. Reset the Powertrain Control Module (PCM) adaptive strategy by disconnecting the battery for more than 5 minutes. This will reset the PCM's BARO calculation to a default value, usually about 150 Hz.

3. Drive the vehicle, and do at least 3 or 4 hard-throttle accelerations, holding at least one for several seconds, as traffic laws will allow, of course.

4. After driving, recheck the BARO reading. If the reading is within range for the shop's elevation, the codes should not return. If the BARO reading has returned to a low reading, and the MAF sensor was just cleaned, it should be replaced, then the reset and drive procedure repeated.
Potential Causes: Contaminated Mass Air Flow (MAF) Sensor
Malfunctioning Mass Air Flow (MAF) Sensor

Tech Tips: The BARO frequency reading on the scan data at sea level is typically 156 Hz, plus or minus 4 Hz, and will go down by about 3 Hz for every 1000 ft above sea level. At 500 ft above sea level, the BARO reading should be above 150 Hz. The BARO reading on scan data is NOT a sensor reading, but rather it is a calculation of vehicle elevation that is made by the Powertrain Control Module (PCM). The PCM calculates BARO mainly by looking at the MAF sensor reading at high throttle openings, and comparing the readings to base sea level readings that are stored in internal memory. As such, just cleaning or replacing the MAF sensor will NOT change the BARO reading. The vehicle must be driven at high throttle openings for the BARO reading to recalculate, or it can be reset by disconnecting the battery for about 10 minutes, or performing a Keep Alive Memory (KAM) reset using a scan tool. Just clearing codes does NOT reset the KAM.
Diagnostic Codes: P0172, P0175
Didn't find what you were looking for?