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Several owners have had issues with this code and its primary cause is a poor ground at the Mass airflow sensor.

Mazda has released a service bulletin with a overlay harness to correct the problem.

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ILLUMINATION - P0172 / P2178 / P2188 SET
APPLICABLE MODEL(S)/VINS
2004-2005 Mazda3 vehicles with VINs lower than JM1BK**** **350581 ( produced before July 1, 2005)

DESCRIPTION
Some vehicles may experience MIL Illumination with DTC P0172 / P2178 / P2188 stored in PCM memory. This may be caused by a poor connection between the terminal and harness wire at the airflow sensor connector.

Other possible causes for this condition are as follow:

Erratic signal from air flow sensor due to foreign material.

Oxygen sensor malfunction.

Engine coolant temperature sensor malfunction.

Purge solenoid valve malfunction.

DTCs vary depending on vehicle.

P0172 (Fuel system too rich) - California Spec 2.0L

P2178 (Fuel system too rich at off idle) - Federal Spec 2.0L All 2.3L

P2188 (Fuel system too rich at idle) - Federal Spec 2.0L All 2.3L

Customers having this concern should have their vehicle repaired using the following repair procedure.

REPAIR PROCEDURE
1. Verify customer concern.
2. Record radio presets.
3. Remove battery cover and battery duct. See Workshop Manual section 01-17 BATTERY REMOVAL / INSTALLATION. Use flat screwdriver to remove clip if necessary.
4. Disconnect negative battery cable using 10mm wrench.
5. Disconnect airflow sensor connector.


6. Identify and carefully cut Black, protective tube of airflow sensor harness using scissors.


7. Using 1/16" (1.7mm) wide pin extractor from Terminal repair kit, remove Black ground wire terminal from airflow sensor connector.


8. Cut off ground wire terminal at base with wire cutter.


9. Remove approximately 1/2" (10mm) of insulation from Black ground wire.


10. This step applies short cord PN - BNYP-67-SH0. Measure from end of short cord opposite terminal end and cut off 1-1/2" (40mm) of wire.


11. Remove approximately 1/2" (10mm) of insulation from new end of short cord.
12. Twist short cord harness wire and Black ground wire together then solder.
CAUTION:

Follow all necessary precautions for safe soldering such as gloves, eye goggles, and respirator.

Place protective cloth under harness to prevent damage from loose solder.






13. Bend soldered ground wire approximately 1-1/2" (40mm) from soldered end. Place heat shrink tubing over soldered end.




14. Using heat gun provided in Terminal repair kit, AKS-630-1010 (or equivalent), heat tube to allow it to shrink. Shrinkage temperature is 250F (120C).
15. Insert modified ground wire terminal into airflow connector until a click it heard, indicating the terminal lock has engaged. Verify that terminal is secure in connector by giving a slight pull.
16. Wrap heat shrink tubing to harness wires using electrical tape.


17. Reconnect airflow sensor connector.
18. Reconnect battery "negative" cable.
NOTE:

If equipped with Mazda Genuine Accessories Remote Start System, follow these steps:

Turn ignition key to ON position.

Connect battery "negative" cable. Horn will "beep" once.

Turn ignition key to OFF position.

Crank engine until it starts one time, then shut engine OFF.


19. Reassembly battery duct and battery cover.
20. Reset radio and clock.
21. Verify repair.