Water intrusion into a connector (X309) located under the cab, beneath the driver's seat, can cause a rough idle, erratic speedometer operation, ABS Light and Check Engine Light illumination, and automatic transmission shifting problems. If needed, connector repair parts are available from Mazda dealers, and possibly some Ford dealers.
Mazda B4000 Problem Reports
RepairPal Verified Mazda B4000 Problem Reports
Rough Running Idle, Erratic Speedometer Operation, ABS Light Illuminated, Check Engine Light, and Automatic Transmission Shifting Problems
A dirty, or contaminated mass airflow sensor (MAF) can cause the engine to run poorly. The Check Engine Light may or may not illuminate. MAF sensor related fault codes P0102 and/or P0103 may be stored. In some cases, carefully cleaning the sensor element will fix the problem. If not, replacement of the sensor may be required.
If the engine cranks but does not start, it may be caused by a tripped inertia switch. Switch the key to "ON" and the fuel pump should be heard running for a second or two. Listen at the gas filler if necessary. The inertia switch is located on the firewall and can be tripped when the parking brake is set too hard and then released. The inertia switch should be reset, and will click when it is reset.
The engine may fail to start due to an electrically shorted sensor. Some of the sensors may internally short and not blow any fuses. A technician may find no spark and no operation of the fuel injectors in the diagnosis. One way a technician may isolate the defective sensor is by disconnecting sensors one by one to see if the engine starts.