Diagnostic procedure

WARNING: This page is about a different car, the 2009 Mazda 6. However, it is still accessible from the selected car via links, so may be relevant.

STEP	INSPECTION	RESULTS	ACTION
1	Remove all the spark plugs Inspect spark plug condition. Is spark plug condition normal?	Yes	Troubleshooting completed
1		No	Specific plug is wet or covered with carbon: Go to the next step Specific plug looks grayish white: Go to Step 7 All plugs are wet or covered with carbon: Go to Step 9. All plugs look grayish white: Go to Step 15.
2	Are the spark plug wet/covered with carbon by the engine oil?	Yes	Inspect all areas related to oil, working up and down.
2		No	Go to the next step
3	Inspect the spark plug for the following. Cracked insulator Heat range Air gap Worn electrode Is the spark plug normal?	Yes	Go to the next step
3		No	Replace the spark plug. (See SPARK PLUG REMOVAL/INSTALLATION [MZI-3.7] .)
4	Inspect compression pressure at suspected malfunctioning cylinder Is compression pressure correct? (See COMPRESSION INSPECTION [MZI-3.7] .)	Yes	Go to the next step
4		No	Repair or replace the malfunctioning part.
5	Install all spark plugs Perform the spark test at suspected malfunctioning cylinder Is strong blue spark visible? (Compare with normal cylinder)	Yes	Go to the next step.
5		No	Repair or replace the malfunctioning part
6	Install the fuel pressure gauge between fuel filter and fuel distributor Measure the fuel line pressure Is the fuel line pressure correct? (See FUEL LINE PRESSURE INSPECTION [MZI-3.7] .)	Yes	Inspect fuel injector for the following Open or short circuit in injector Leakage Injection volume
6		No	Zero or low: Inspect the fuel pump relay and fuel pump circuit. Inspect the fuel line for clogging If there is no malfunction, replace the fuel pump unit. (See FUEL PUMP UNIT REMOVAL/INSTALLATION [MZI-3.7] .) High: Replace the fuel pump unit (See FUEL PUMP UNIT REMOVAL/INSTALLATION [MZI-3.7] .)
7	Inspect the spark plug for the following. Heat range Air gap Is the spark plug normal?	Yes	Go to the next step.
7		No	Replace the spark plug (See SPARK PLUG REMOVAL/INSTALLATION [MZI-3.7] .)
8	Remove the suspected fuel injector. Inspect the following Resistance Fuel injection volume (See FUEL INJECTOR INSPECTION [MZI-3.7] .) Are all above items normal?	Yes	Inspect for open circuit in wiring harness between fuel injector connector terminal A and PCM at the following terminals For No. 1 cylinder: 2BQ For No. 2 cylinder: 2BC For No. 3 cylinder: 2AY For No. 4 cylinder: 2BG For No. 5 cylinder: 2BL For No. 6 cylinder: 2BI
8		No	Replace the fuel injector
9	Is the air cleaner element free of clogging?	Yes	Go to the next step
9	Is the air cleaner element free of clogging?	No	Replace the air cleaner element
10	Perform the spark test (See ENGINE CONTROL SYSTEM OPERATION INSPECTION [MZI-3.7] .) Is strong blue spark visible at each cylinder?	Yes	Go to the next step
10		No	Repair or replace the malfunctioning part
11	Install the fuel pressure gauge between the fuel filter and fuel distributor Measure the fuel line pressure. Is the fuel line pressure correct? (See FUEL LINE PRESSURE INSPECTION [MZI-3.7] .)	Yes	Go to the next step.
11		No	Zero or low: Perform "Fuel Pump Operation Inspection" and "Fuel Pump Control System Operation Inspection", repair or replace according to inspection results Inspect the fuel line for clogging If there is no malfunction, replace the fuel pump unit (See FUEL PUMP UNIT REMOVAL/INSTALLATION [MZI-3.7] .) High: Perform "Fuel Pump Control System Operation Inspection", repair or replace according to inspection results. If there is no malfunction, replace the fuel pump unit. (See FUEL PUMP UNIT REMOVAL/INSTALLATION [MZI-3.7] .)
12	Inspect the following PIDs ECT O2S11 (When engine can be started.) O2S12 (When engine can be started) O2S21 (When engine can be started.) O2S22 (When engine can be started) MAF (See PCM INSPECTION [MZI-3.7] .) Are PIDs normal?	Yes	Go to the next step
12		No	Repair or replace the malfunctioning part
13	Perform the purge control inspection. (When engine can be started.) (See ENGINE CONTROL SYSTEM OPERATION INSPECTION [MZI-3.7] .) Is the purge control correct?	Yes	Go to the next step.
13		No	Repair or replace the malfunctioning part
14	Perform compression inspection. (See COMPRESSION INSPECTION [MZI-3.7] .) Is compression correct?	Yes	Visually inspect for deformed exhaust system part If normal replace the fuel (Poor quality fuel is used)
14		No	Repair or replace the malfunctioning part
15	When the engine cannot be started, inspect the Intake-air system for air leakage. When the engine can be started, perform intake manifold vacuum inspection. Is air sucked in from intake-air system?	Yes	Repair or replace the malfunctioning part.
15		No	Go to the next step.
16	Install the fuel pressure gauge between the fuel filter and the fuel distributor. Measure the fuel line pressure Is fuel line pressure correct? (See FUEL LINE PRESSURE INSPECTION [MZI-3.7] .)	Yes	Inspect the following PIDs: ECT O2S11 O2S12 O2S21 O2S22 MAF (See PCM INSPECTION [MZI-3.7] .) Inspect PCM GND condition.
16		No	Zero or low: Perform "Fuel Pump Operation Inspection" and "Fuel Pump Control System Operation Inspection", repair or replace according to inspection results. Inspect the fuel line for clogging. If there is no malfunction, replace the fuel pump unit (See FUEL PUMP UNIT REMOVAL/INSTALLATION [MZI-3.7] .) High: Perform "Fuel Pump Control System Operation Inspection", repair or replace according to inspection results. If there is no malfunction, replace the fuel pump unit (See FUEL PUMP UNIT REMOVAL/INSTALLATION [MZI-3.7] .)
17	Verify test results If normal, return to diagnostic index to service any additional symptoms. (See SYMPTOM DIAGNOSTIC INDEX [MZI-3.7] .) 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 the PCM if a later calibration is available. Retest.