Diagnostic procedure

WARNING: This page is about a different car, the 2005 Mazda RX-8. However, it is still accessible from the selected car via links, so may be relevant.

DTC P0638 DIAGNOSTIC PROCEDURE

STEP	INSPECTION		ACTION
1	VERIFY FREEZE FRAME DATA HAS BEEN RECORDED Has FREEZE FRAME DATA been recorded?	Yes	Go to the next step.
1		No	Record the FREEZE FRAME DATA on the repair order, then go to the next step.
2	VERIFY RELATED REPAIR INFORMATION AVAILABILITY Verify related Service Bulletins and/or on-line repair information availability. Is any related repair information available?	Yes	Perform repair or diagnosis according to the available repair information. If the vehicle is not repaired, go to the next step.
2		No	Go to the next step.
3	VERIFY RELATED PENDING CODE OR STORED DTC Turn the ignition switch off, then to the ON position (Engine off). Verify the related PENDING CODE or stored DTCs. Are other DTCs present?	Yes	Go to the applicable DTC inspection. (See DTC TABLE .)
3		No	Go to the next step.
4	INSPECT DRIVE-BY-WIRE CONTROL SYSTEM OPERATION Perform the "Drive-by-wire Control System Inspection". (See DRIVE-BY-WIRE CONTROL SYSTEM INSPECTION .) Is there any malfunction?	Yes	Repair or replace the malfunctioning part according to the inspection results. Then go to Step 7.
4		No	Go to the next step.
5	INSPECT THROTTLE ACTUATOR Inspect the throttle actuator. (See RESISTANCE INSPECTION .) Is there any malfunction?	Yes	Replace the throttle body, then go to Step 7. (See INTAKE-AIR SYSTEM REMOVAL/INSTALLATION .)
5		No	Go to the next step.
6	INSPECT THROTTLE VALVE Inspect the throttle valve. (See THROTTLE VALVE INSPECTION .) Is there any malfunction?	Yes	Replace the throttle body, then go to the next step. (See INTAKE-AIR SYSTEM REMOVAL/INSTALLATION .)
6		No	Go to the next step.
7	VERIFY TROUBLESHOOTING OF P0638 COMPLETED Make sure to reconnect all disconnected connectors. Clear the DTC from the PCM memory using the WDS or equivalent. Start the engine. Is the same DTC present?	Yes	Replace the PCM, go to the next step. (See PCM REMOVAL/INSTALLATION .)
7		No	Go to the next step.
8	VERIFY AFTER REPAIR PROCEDURE Perform the "AFTER REPAIR PROCEDURE". (See AFTER REPAIR PROCEDURE .) Are any DTCs present?	Yes	Go to the applicable DTC inspection. (See DTC TABLE .)
8		No	DTC troubleshooting completed.