Diagnostic procedure

WARNING: This page is about a different car, the 2005 Mazda 6. However, it is still accessible from the selected car via links, so may be relevant.

NO. 14 POOR FUEL ECONOMY [AJ] DIAGNOSTIC PROCEDURE

STEP	INSPECTION		ACTION
1	Inspect following: Air cleaner element for contamination ATF level (ATX) Fuel quality Coolant level Clutch slippage (MTX) Are all items okay?	Yes	Go to the next step.
1		No	Service as necessary. Repeat Step 1.
2	Connect WDS or equivalent to DLC-2. Tun ignition switch to ON position (Engine OFF). Retrieve any DTCs. Are there any DTCs displayed?	Yes	DTC is displayed: Go to appropriate DTC test.
2		No	No DTC is displayed: Go to the next step.
3	Access ECT PID. Drive vehicle while monitoring PID. (See PCM INSPECTION .) Is PID within specification?	Yes	Go to the next step.
3		No	Inspect for coolant leakage. Inspect cooling fan operations or thermostat operations.
4	Perform spark test. (See SPARK TEST .) Is strong blue spark visible at each cylinder?	Yes	Inspect for following: Spark plugs malfunction CMP sensor is installed improperly. Trigger wheel damage on camshaft Open or short circuit on CMP sensor Open or short circuit between CMP sensor and PCM terminal 80, 54, 28 or 2. Repair or replace malfunctioning part. If okay, go to the next step.
4		No	Repair or replace malfunctioning part according to spark test results.
5	Install fuel pressure gauge between fuel filter and fuel distributor. Start engine and run it at idle. Measure fuel line pressure at idle. (See FUEL LINE PRESSURE INSPECTION .) Is fuel line pressure correct at idle?	Yes	Go to the next step.
5		No	Zero or low: Inspect fuel pump relay and fuel pump circuit. Inspect for clogged fuel line. If okay, replace fuel pump unit. (See FUEL PUMP UNIT REMOVAL/INSTALLATION .) High: Replace fuel pump unit. (See FUEL PUMP UNIT REMOVAL/INSTALLATION .)
6	Remove and shake PCV valve. Does PCV valve rattle?	Yes	Go to the next step.
6	Remove and shake PCV valve. Does PCV valve rattle?	No	Replace PCV valve.
7	Inspect for restriction in the exhaust system. Is there any restriction?	Yes	Inspect exhaust system.
7		No	Go to the next step.
8	Is brake system functioning properly?	Yes	Go to the next step.
8	Is brake system functioning properly?	No	Inspect for cause.
9	Inspect MAF sensor for contamination. (See MASS AIR FLOW (MAF) SENSOR INSPECTION .) Is there any contamination?	Yes	Replace MAF/IAT sensor.
9		No	Go to the next step.
10	Perform variable valve timing control system inspection. (See VARIABLE VALVE TIMING CONTROL SYSTEM OPERATION INSPECTION .) Does variable valve timing control system work properly?	Yes	Go to the next step.
10		No	Repair or replace malfunctioning part according to variable valve timing control system inspection results.
11	Is engine compression correct? (See COMPRESSION INSPECTION .)	Yes	Inspect valve timing.
11		No	Inspect for cause.
12	Verify test results. If okay, return to diagnostic index to service any additional symptoms. If malfunction remains, inspect related Service Bulletins and/or On-line Repair Information and perform repair or diagnosis. If vehicle is repaired, troubleshooting completed. If vehicle is not repaired or additional diagnostic information is not available, reprogram PCM if later calibration is available. Retest.