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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 DIAGNOSTIC PROCEDURE

STEP INSPECTION RESULTS ACTION
1 Inspect for the following:
  • Air cleaner element for contamination
  • ATF level (ATX)
  • Fuel quality
  • Coolant level
  • Brake dragging
  • Clutch slippage (MTX)

Are all items normal?		 Yes Go to the next step.
No Service if necessary.
Repeat Step 1.
2 Connect WDS or equivalent to DLC-2.
Turn ignition switch to ON position (Engine off).
Retrieve any DTCs.
Are there any DTCs displayed?		 Yes DTC is displayed: 
Go to appropriate DTC test.
No No DTC is displayed: 
3 Access ECT PID.
Drive vehicle while monitoring PID.
(See PCM INSPECTION .)
Is PID within specification?		 Yes Go to the next step.
Go to the next step.
No Inspect for coolant leakage, cooling fan and condenser fan operations or thermostat operation.
4 Perform spark test. (See SPARK TEST (CALIFORNIA EMISSION REGULATION APPLICABLE ATX MODEL) )
(See SPARK TEST (EXCEPT FOR CALIFORNIA EMISSION REGULATION APPLICABLE ATX MODEL) )
Is strong blue spark visible at each cylinder		 Yes Inspect for the following:
  • Spark plugs malfunction
  • CMP sensor is improperly installed.
  • Trigger wheel damage on camshaft
  • Open or short circuit on CMP sensor
  • Open or short circuit between CMP sensor and PCM terminal 2(1), 28(1), 2J(2) or 2M(2)

Repair or replace malfunctioning parts.
If okay, go to the next step.
No Inspect following:
  • High-tension leads(2)
  • Ignition coil and connector
5 Install fuel pressure gauge between fuel pipe and fuel distributor.
Start engine and idle it.
Measure fuel line pressure during idle.
Is fuel line pressure correct during idle?
(See FUEL LINE PRESSURE INSPECTION .)		 Yes Go to the next step.
No Zero or low: 
Inspect fuel pump relay and fuel pump circuit.
Inspect for clogged fuel line.
If okay, replace fuel pump unit
High: 
Replace fuel pump unit.
6 Inspect for Variable tumble system operation.
(See VARIABLE TUMBLE SYSTEM OPERATION INSPECTION .)
Does Variable tumble system work properly?		 Yes Go to the next step.
No Repair or replace malfunctioning parts.
7 Inspect for variable valve timing control system operation.
(See VARIABLE VALVE TIMING CONTROL SYSTEM OPERATION INSPECTION .)
Does variable valve timing control system work properly?		 Yes Go to the next step.
No Repair or replace malfunctioning parts.
8 Inspect for Variable intake air system operation.
(See VARIABLE INTAKE AIR SYSTEM OPERATION INSPECTION .)
Does Variable intake air system work properly		 Yes Go to the next step.
No Repair or replace malfunctioning parts.
9 Remove and shake PCV valve.
Does PCV valve rattle		 Yes Go to the next step.
No Replace PCV valve.
10 Inspect for restriction in the exhaust system.
Is there any restriction?		 Yes Inspect exhaust system.
No Go to the next step.
11 Inspect for contaminated MAF sensor.
Is there any contamination?		 Yes Go to the next step.
No Inspect for cause.
12 Inspect MAF sensor for contamination.
Is there any contamination?		 Yes Replace MAF sensor.
No Go to the next step.
13 Is engine compression correct Yes Inspect valve timing.
No Inspect for cause.
14 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.
(1) California emission regulation applicable ATX model
(2) Except for California emission regulation applicable ATX model
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