MAF Diagnostic Service Tip - Vehicles Equipped With EGR System Module (ESM) (05-3-1)

MAF DIAGNOSTIC SERVICE TIP - VEHICLES EQUIPPED WITH EGR SYSTEM MODULE (ESM)

TECHNICAL SERVICE BULLETIN

DESCRIPTION

MAF DIAGNOSTIC SERVICE TIP - VEHICLES EQUIPPED WITH EGR SYSTEM MODULE (ESM)

ISSUE

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.

ACTION

Refer to the following Service Tips to aid in diagnosing MAF and other malfunction indicator lamp (MIL)/driveability concerns, using the BARO PID.

SERVICE TIPS

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:

1. 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.
2. 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.
3. 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.

DIAGNOSTICS

1. 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.
2. Do not reset KAM.
3. Make sure the key is off for at least 1 minute.
4. Connect the scan tool.
5. Turn key on, do not start the engine.
6. Setup scan tool to read BARO PID and MAP_V (MAP sensor voltage).
7. Verify if BARO PID and MAP voltage matches barometric pressure for appropriate geographical location using the barometric pressure/MAP sensor reference chart in Fig 2 . (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.)
   1. 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.
      1. Check ESM wires and connections for shorts and opens.
      2. 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.
         Fig 1: ESM Connector Pins

         

WARRANTY INFORMATION

WARRANTY STATUS:  Information Only.