Engines use masses of air for combustion and it has to be measured somehow for the computers to know how much fuel to mix in. When these systems malfunction, they can cause all sorts of issues. Follow this Real Fix to see how a mass airflow sensor on this Mazda CX-9 was diagnosed and repaired.
Vehicle
2011 Mazda CX-9 Touring 3.7L
Title
P2195, P2197, Replaced Mass Airflow Sensor
Complaint
The customer states the check engine light is on.
Cause
Connected a scan tool and found codes: P2195 – O2 Sensor Signal Biased/Stuck Lean (Bank 1 Sensor 1) and P2197 – O2 Sensor Signal Biased/Stuck Lean (Bank 2 Sensor 1). Used the scan tool to monitor live data and observed the mass airflow sensor parameter was not within the specified range of approximately 0.7 Volts. Inspected the mass airflow sensor wiring harness and connector, but detected no obvious faults. With the ignition on and the engine off, used a multi-meter to check for the presence of voltage and ground at the mass airflow sensor connector and found both were present. Used a lab scope to backprobe the mass airflow sensor and found the mass airflow sensor signal was above the specified 0.7 volts at idle, opened the throttle and observed the mass airflow signal was erratic. These test results verified the mass airflow sensor was faulty.
Correction
Replaced the mass airflow sensor, cleared codes, performed a road test and verified the vehicle operated properly. The check engine light did not illuminate and no fault codes returned.