
Diagnostic procedure

Dtc 21
Dtc 31Mazda 6 Service Manual: Heater core inspection
1. Remove the A/C unit. (See A/C UNIT REMOVAL/INSTALLATION.)
2. Remove the heater core from the A/C unit.
3. Inspect for cracks, damage, and coolant leakage.
If any problems are found, replace the heater core.
4. Inspect for bent fins.
If any are bent, use a flathead screwdriver to stra ...
Mazda 6 Service Manual: Turning the Engine Off
WARNINGDo not stop the engine while the vehicle is moving: Stopping the
engine while the vehicle is moving for any reason other than in an emergency is
dangerous. Stopping the engine while the vehicle is moving will result in reduced
braking ability due to the loss of power braking, which coul ...