Mazda 6. Manual - part 169

F–198

TROUBLESHOOTING 

End Of Sie

NO.7 SLOW RETURN TO IDLE

A6E398018881W09

Diagnostic procedure

End Of Sie

26

Is air leakage felt or heard at intake-air system 
components while racing engine  to higher 
speed?

Yes

Repair or replace.

No

Go to next step.

27

Inspect engine condition while tapping EGR 
valve housing.
Is engine condition improved?

Yes

Replace EGR valve.

No

Go to next step.

28

Note

• The following test should be performed for 

vehicles with variable valve timing control 
system. Go to next step for vehicles 
without variable valve timing control 
system.

Inspect variable valve timing control system 
operation.
(See 

F–239 Variable Valve Timing Control 

System Operation Inspection

.)

Does variable valve timing control work 
properly?

Yes

Go to next step.

No

Repair or replace malfunctioning parts.

29

Is engine compression correct?

Yes

Inspect valve timing.

No

Inspect for causes.

30

Verify test results.

• If okay, return to diagnostic index to service any additional symptoms.

• If malfunction remains, replace PCM.

STEP

INSPECTION

RESULTS

ACTION

7

SLOW RETURN TO IDLE

DESCRIPTION

Engine takes more time than normal to return to idle speed.

POSSIBLE CAUSE

• ECT sensor malfunction

• Thermostat is stuck open.

• Throttle body malfunction

• Air leakage from intake-air system

STEP

INSPECTION

RESULTS

ACTION

1

Connect WDS or equivalent to DLC-2.
Retrieve any continuous memory, KOEO and 
KOER DTCs.
Are there DTCs displayed?

Yes

DTC is displayed:
Go to appropriate DTC test.

No

No DTC is displayed:
Go to next step.

2

Remove thermostat and inspect operation.

(See 

E–7 THERMOSTAT REMOVAL/

INSTALLATION

.)

(See 

E–8 THERMOSTAT INSPECTION

.)

Is thermostat okay?

Yes

ECT and thermostat are okay.
Go to next step.

No

Access ECT PID on WDS or equivalent.
Inspect for both ECT PID and temperature gauge on 
instrument cluster readings.
If temperature gauge on instrument cluster indicates 
normal range but ECT PID is not same as temperature 
gauge reading, inspect ECT sensor.
If temperature gauge on instrument cluster indicates 
cold range but ECT PID is normal, inspect temperature 
gauge and heat gauge unit.

3

Is throttle body free of contaminations?

Yes

Inspect for air leakage from intake-air system 
components while racing engine to higher speed.

No

Clean or replace throttle body.

4

Verify test results.

• If okay, return to diagnostic index to service any additional symptoms.

• If malfunction remains, replace PCM.

TROUBLESHOOTING 

F–199

F

NO.8 ENGINE RUNS ROUGH/ROLLING IDLE

A6E398018881W10

Diagnostic procedure

8

ENGINE RUNS ROUGH/ROLLING IDLE

DESCRIPTION

• Engine speed fluctuates between specified idle speed and lower speed and engine shakes 

excessively.

• Idle speed is too slow and engine shakes excessively.

POSSIBLE CAUSE

• Air leakage from intake-air system parts

• A/C system operation is improper

• Spark leakage from high-tension leads

• Spark plug malfunction

• Purge solenoid valve malfunction

• IAC valve improper operation

• EGR valve malfunction

• Erratic or no signal from CMP sensor

• Low engine compression

• Improper valve timing

• Improper variable valve timing control system operation (L3-VE)

• Erratic signal from CKP sensor

• Poor fuel quality

• PCV valve malfunction

• Air cleaner restriction

• Restriction in exhaust system

• Disconnected electrical connectors

• Inadequate fuel pressure

• Fuel pump body mechanical malfunction

• Improper load signal input

• Fuel line restriction or clogging

• Improper fuel injection control operation

• Fuel leakage from fuel injector

• Fuel injector clogging

• Engine overheating

• Vacuum leakage

• Pressure regurator malfunction

Warning
The following troubleshooting flow chart contains fuel system diagnosis and repair 
procedures. Read following warnings before performing the fuel system services:

• Fuel vapor is hazardous. It can easily ignite, causing serious injury and damage. Always 

keep sparks and flames away from fuel.

• Fuel line spills and leakage are dangerous. Fuel can ignite and cause serious injuries or 

death and damage. Fuel can also irritate skin and eyes. To prevent this, always complete 
“BEFORE REPAIR PROCEDURE” and “AFTER REPAIR PROCEDURE” described in this 
manual.
(See 

F–17 BEFORE REPAIR PROCEDURE

.)

(See 

F–17 AFTER REPAIR PROCEDURE

.)

Caution

• Disconnecting/connecting quick release connector without cleaning it may possibly cause 

damage to fuel pipe and quick release connector. Always clean quick release connector 
joint area before disconnecting/connecting, and make sure that it is free of foreign material.

STEP

INSPECTION

RESULTS

ACTION

1

Verify following:

• External fuel shut off or accessory (kill 

switch, alarm etc.)

• Fuel quality (e.g. proper octane, 

contamination, winter/summer blend)

• No air leakage from intake-air system

• Proper sealing of intake manifold and 

components attached to intake manifold:  
EGR valve, IAC valve

• Ignition wiring

• Electrical connections

• Fuses

• Smooth operation of throttle valve

Are all items okay?

Yes

Go to next step.

No

Service as necessary.
Repeat Step 1.

F–200

TROUBLESHOOTING 

2

Connect WDS or equivalent to DLC-2.
Retrieve any continuous memory, KOEO and 
KOER.
Are there any DTCs displayed?

Yes

DTC is displayed:
Go to appropriate DTC test.

No

No DTC is displayed:
Go to next step.

3

Is engine overheating?

Yes

Go to symptom troubleshooting "No.17 Cooling system 
concerns - Overheating".

No

Go to next step.

4

Note

• Following test is for engine running rough 

idle with A/C on concerns. If other 
symptoms exist, go to next step.

Connect pressure gauge to A/C low and high 
pressure side lines.
Start engine and run it at idle.
Turn A/C switch on.
Measure low side and high side pressures.
Are pressures within specifications?
(See 

U–12 REFRIGERANT PRESSURE 

CHECK

.)

Yes

Go to next step.

No

If A/C is always on, go to symptom troubleshooting 
"No.24 A/C is always on or A/C compressor runs 
continuously".
For other symptoms, inspect following:

• Refrigerant charging amount

• Condenser fan operation

5

Note

• Following test is for engine running rough 

with P/S on. If other symptoms exist, go to 
next step.

Start engine and run it at idle.
Access PSP PID.
Inspect if PSP PID is on while turning steering 
wheel right to left.
Is PSP PID okay?

Yes

Inspect power steering pressure switch operation and 
wiring harness between P/S pressure switch connector 
and PCM connector terminal 1Z.

No

Go to next step.

6

Visually inspect CKP sensor and teeth of 
crankshaft pulley.
Are CKP sensor and teeth of crankshaft pulley 
okay?

Yes

Go to next step.

No

Replace malfunctioning parts.

7

Measure gap between CKP sensor and teeth of 
crankshaft pulley.

Specification

0.5—1.5 mm {0.020—0.075 in}

Is gap within specification?

Yes

Go to next step.

No

Adjust CKP sensor.

8

Inspect for cracks on high-tension leads.
Are there any cracks on high-tension leads?

Yes

Repair suspected high-tension leads.

No

Go to next step.

9

Inspect spark plug condition.
Is spark plug wet, covered with carbon or 
grayish white?

Yes

Spark plug is wet or covered with carbon:
Inspect for fuel leakage from injector.
Spark plug is grayish white:
Inspect for clogged fuel injector.

No

Install spark plugs on original cylinders.
Go to next step.

10

Start engine and disconnect IAC valve 
connector.
Does rpm drop or engine stall?

Yes

Go to next step.

No

Inspect IAC valve and wiring harness.

11

Install fuel pressure gauge between fuel pipe 
and fuel distributor.
Start engine and run it at idle.
Measure fuel line pressure at idle.
Is fuel line pressure correct at idle?
(See 

F–20 FUEL LINE PRESSURE 

INSPECTION

)

Yes

Go to next step.

No

Zero or low:
Inspect for clogged fuel line.
If okay, replace fuel pump unit.
High:
Replace fuel pump unit.

12

Visually inspect for fuel leakage at fuel injector, 
O-ring, and fuel line.
Service as necessary.
Does fuel line pressure hold after ignition switch 
is turned off?
(See 

F–20 FUEL LINE PRESSURE 

INSPECTION

)

Yes

Go to next step.

No

Inspect fuel injector.
If fuel injector is okay, replace fuel pump unit.

STEP

INSPECTION

RESULTS

ACTION

TROUBLESHOOTING 

F–201

F

End Of Sie

NO.9 FAST IDLE/RUNS ON

A6E398018881W11

Diagnostic procedure

13

Connect WDS or equivalent to DLC-2.
Start the engine and run it at idle.
Access O2S11 PID.
Is O2S11 PID okay?

• More than 0.45 V when accelerator pedal is 

suddenly depressed: rich condition

• Less than 0.45 V during fuel cut: lean 

condition

Yes

Go to next step.

No

Inspect and repair or replace faulty HO2S, harness, 
connector or terminal, then go to next step.

14

Disconnect vacuum hose between purge 
solenoid valve and intake manifold from  purge 
solenoid valve side. 
Plug opening end of vacuum hose. Start engine.
Does engine condition improve?

Yes

Inspect if purge solenoid valve sticks open 
mechanically.
Inspect EVAP control system.

No

Go to next step.

15

Remove and shake PCV valve.
Does PCV valve rattle?

Yes

Go to next step.

No

Replace PCV valve.

16

Inspect for restriction in exhaust system.
Is there any restriction?

Yes

Inspect exhaust system.

No

Go to next step.

17

Visually inspect CMP sensor and teeth of 
camshaft.
Are CMP sensor and teeth of camshaft okay?

Yes

Go to next step.

No

Replace malfunctioning parts.

18

Inspect engine condition while tapping EGR 
valve housing. 
Does engine condition improve?

Yes

Replace EGR valve.

No

Go to next step.

19

Note

• The following test should be performed for 

vehicles with variable valve timing control 
system. Go to next step for vehicles witout 
variable valve timing control system.

Inspect variable valve timing control system 
operation.
(See 

F–239 Variable Valve Timing Control 

System Operation Inspection

.)

Does variable valve timing control system work 
properly?

Yes

Go to next step.

No

Repair or replace malfunctioning parts.

20

Is engine compression correct?

Yes

Inspect valve timing.

No

Inspect for causes.

21

Verify test results.

• If okay, return to diagnostic index to service any additional symptoms.

• If malfunction remains, replace PCM.

STEP

INSPECTION

RESULTS

ACTION

9

FAST IDLE/RUNS ON

DESCRIPTION

• Engine speed continues at fast idle after warm-up.

• Engine runs after ignition switch is turned off.

POSSIBLE CAUSE

• ECT sensor malfunction

• Air leakage from intake-air system

• Throttle body malfunction

• Accelerator cable free play misadjustment

• Cruise control cable misadjustment

• Improper load signal input

STEP

INSPECTION

RESULTS

ACTION

1

Connect WDS or equivalent to DLC-2.
Access ECT PID.
Start and warm up engine to normal operating 
temperature.
Is ECT PID reading between 82—112

°C {180—

234

°F}?

Yes

Go to next step.

No

ECT PID is higher than 112

°C {234°F}:

Go to symptom troubleshooting "No.17 Cooling system 
concerns - Overheating".
ECT PID is less than 82

°C {180°F}:

Go to symptom troubleshooting "No.18 Cooling system 
concerns - Runs cold".