MAF DIAGNOSTIC SERVICE TIP - VEHICLES EQUIPPED WITH EGR SYSTEM MODULE (ESM)
Publication Date: January 28, 2005
2003-2005 Crown Victoria, Thunderbird 2005 Five Hundred, Ford GT, Freestyle, Mustang 2004-2005 Explorer, F-150, Freestar 2005 E-Series
2003-2005 LS, Town Car, Aviator
2003-2005 Grand Marquis 2005 Montego 2004-2005 Monterey, Mountaineer
When diagnosing for a possible MAF sensor related condition, on a vehicle equipped with an EGR system module (ESM), an incorrect engine-running BARO value is no longer a reliable indicator of a skewed MAF sensor. Vehicles with ESM use both the MAP and MAF for engine-running BARO updates. Replacing the MAF sensor for a seemingly incorrect or inconsistent key-on BARO is not an effective repair for vehicles equipped with an ESM.
Refer to the following Service Tips to aid in diagnosing MAF and other malfunction indicator lamp (MIL)/driveability concerns, using the BARO PID.
SOME EARLY BUILT 2003 VEHICLES EQUIPPED WITH AN ESM MAY NOT HAVE THE STRATEGY/CALIBRATION TO UPDATE THE BARO PID USING THE ESM'S MAP SENSOR. IN THESE APPLICATIONS THE BARO WILL BE UPDATED BY THE MAF SENSOR, OR IF FAULTS ARE PRESENT A DEFAULT VALUE WILL BE SET (DEFAULT VALUE MAY DIFFER DEPENDING ON APPLICATION AND STRATEGY). DIAGNOSE THESE APPLICATIONS WITH THE CURRENT PROCEDURES WITHOUT USING THE ESM'S BARO METHODS.
THE BAROMETRIC PRESSURE/MAP SENSOR REFERENCE CHART CONTAINED IN THIS TSB SHOWS THE ESM'S MAP SENSOR VOLTAGE CORRESPONDING TO A BARO READING IN INCHES OF MERCURY (IN-HG) AND IN HERTZ (HZ). THE CONVERSION TO KILO PASCALS (KPA) AND POUNDS PER SQUARE INCHES (PSI) ARE ALSO PROVIDED IN THE CHART.
The ESM calculates EGR delta pressure using two (2) MAP sensors that independently read intake manifold and exhaust pressure. This allows vehicles with an ESM to use a MAP sensor to obtain a BARO reading from the intake manifold, prior to engine start.
There are three (3) ways for the BARO PID to update in vehicles equipped with an ESM:
BARO is adjusted to a value based on the ESM's MAP sensor reading during key-on prior to engine start. There must be a minimum of 1 minute key-off time to get the BARO to update, prior to turning the key to the start/run position.
BARO may also be adjusted based on MAF and MAP sensors readings under certain driving conditions, as long as no DTCs or faults are present. Typical conditions are stabilized engine temperatures and high to moderate throttle openings.
BARO will adjust to a default value if faults are presents or the keep alive memory (KAM) is cleared. A low battery voltage or a KAM reset performed by a scan tool will clear KAM. The default value depends on how the vehicle application was calibrated. (example the BARO value may read 27 in-Hg (150Hz) when the KAM was cleared, but the actually barometric pressure due to geographical region may be different.) Use the following verification method to check BARO.
TO VERIFY BARO IN VEHICLES EQUIPPED WITH ESM'S YOU WILL NEED A SCAN TOOL AND THE BAROMETRIC PRESSURE/MAP SENSOR REFERENCE CHART.
If DTCs other than P2106, P0106, P0107, P0401, P0402 are present, repair these first. If the KAM is reset during the repairs then proceed to Step 3.
Do not reset KAM.
Make sure the key is off for at least 1 minute.
Connect the scan tool.
Turn key on, do not start the engine.
Setup scan tool to read BARO PID and MAP_V (MAP sensor voltage).
Verify if BARO PID and MAP voltage matches barometric pressure for appropriate geographical location using the barometric pressure/MAP sensor reference chart. (Example, if the MAP_V reads approximately 4.20 V then the BARO PID should read about 156Hz which would correspond to a region where the barometric pressure is approximately 29 in-HG. Verify with local weather reports and altitude readings.)
If the key-on BARO is not appropriate for the geographical region verify the MAP sensor is putting out the correct voltage by comparing MAP_V PID and the actual voltage at pin-3 of the ESM (use pin-6 for the ground reference). If there is a discrepancy greater than 0.2 volts then perform the following checks.
Check ESM wires and connections for shorts and opens.
Check for internal ESM short. Check resistance between pin-2 (VREF) and pin-6 (signal return) on the ESM with ESM harness disconnected. If resistance is less then 2000 OHMS then replace ESM and retest.