Mazda CX-9 Grand Touring. Manual - part 237

DTC P0128 [MZI-3.7] 

DTC P0128 (MZI-3.7) DETECTION CONDITIONS AND POSSIBLE CAUSES 

DIAGNOSTIC PROCEDURE 

DTC P0128 (MZI-3.7) DIAGNOSTIC PROCEDURE 



Are there any malfunction?  

No

Go to the next step.

8

VERIFY TROUBLESHOOTING OF 
DTC P0123 HAS BEEN COMPLETED  



Make sure to reconnect all 
disconnected connectors.  



Clear the DTC from the PCM memory 
using the M-MDS.  



Start the engine.  



Perform the "KOEO/KOER self-test". 
(See KOEO/KOER SELF TEST 
[MZI-3.7].)  



Is same DTC present?  

Yes

Replace the PCM, then go to the next step. (See 
PCM REMOVAL/INSTALLATION [MZI-
3.7] .)

No

Go to the next step.

9

VERIFY AFTER REPAIR PROCEDURE
 



Perform the "AFTER REPAIR 
PROCEDURE". (See AFTER 
REPAIR PROCEDURE [MZI-3.7].) 



Are any DTCs present?  

Yes

Go to the applicable DTC inspection. (See DTC 
TABLE [MZI-3.7].)

No

Troubleshooting completed.

DTC P0128

Coolant thermostat (coolant temp below thermostat regulating temperature)

DETECTION 

CONDITION 



P0128 Indicates that the thermostat monitor has not achieved the required 
engine operating temperature within a specified amount of time after starting 
the engine.  

POSSIBLE CAUSE 



Insufficient warm up time  



Low engine coolant level  



Leaking or stuck open thermostat  



Inoperative cylinder head temperature (CHT) sensor  

STEP

INSPECTION

ACTION

1

VERIFY FREEZE FRAME DATA HAS BEEN 
RECORDED  



Has FREEZE FRAME DATA been 
recorded?  

Yes Go to the next step.

No

Record FREEZE FRAME DATA on the 

repair order, then go to the next step.

VERIFY RELATED REPAIR INFORMATION 

Perform repair or diagnosis according to 

 

2008 Mazda CX-9 Grand Touring 

2008 ENGINE PERFORMANCE On-Board Diagnostic (MZI-3.7) - Mazda CX-9

  

Microsoft 

 

Sunday, November 15, 2009 10:08:35 AM

Page 81 

© 2005 Mitchell Repair Information Company, LLC. 

2

AVAILABILITY  



Verify related Service Bulletins and/or on-
line repair information availability.  



Is any related Service Bulletins available?  

Yes

the available Service Bulletins. 



If the vehicle is not repaired, go to 
the next step.  

No

Go to the next step.

3

INSPECT ENGINE COOLANT LEVEL 

 



Is the engine coolant fill level correct?  

WARNING:



Never remove the cooling system cap or 
loosen the radiator drain plug while the 
engine is running, or when the engine and 
radiator are hot. Scalding engine coolant 
and steam may shoot out and cause 
serious injury. It may also damage the 
engine and cooling system.  



Turn off the engine and wait until it is cool. 
Even then, be very careful when removing 
the cap. Wrap a thick cloth around it and 
slowly turn it counterclockwise to the first 
stop. Step back while the pressure 
escapes.  



When you're sure all the pressure is gone, 
press down on the cap using the cloth, 
turn it, and remove it.  

Yes Go to the next step.

No

Inspect for a loss of engine coolant. 

Repair if necessary. (See ENGINE 

COOLANT LEVEL INSPECTION 

[MZI-3.7] .) 

Go to Step 5.

4

INSPECT SENSOR OPERATION  



Run the engine until the engine temperature 
stabilizes.  



Verify that the radiator hoses are hot and the 
cooling system is pressurized.  



Access the PCM and monitor the CHT PID.  



Is the temperature more than 77°C {170.6°
F}?  

Yes The test is complete. Go to the next step.

No

Inspect the thermostat operation. Repair 

if necessary. (See THERMOSTAT 

INSPECTION [MZI-3.7] .)

5

VERIFY TROUBLESHOOTING OF DTC 
P0128 HAS BEEN COMPLETED  



Verify that all disconnected connectors are 
reconnected.  



Turn the ignition switch to the ON position 
(Engine off).  



Clear the DTC from the PCM memory using 
the M-MDS.  

Yes

Replace PCM, then go to the next step. 
(See PCM 
REMOVAL/INSTALLATION [MZI-
3.7] .)

 

2008 Mazda CX-9 Grand Touring 

2008 ENGINE PERFORMANCE On-Board Diagnostic (MZI-3.7) - Mazda CX-9

  

Microsoft 

 

Sunday, November 15, 2009 10:08:35 AM

Page 82 

© 2005 Mitchell Repair Information Company, LLC. 

DTC P0132, P0138, P0152, P0158 [MZI-3.7] 

DTC P0128 (MZI-3.7) DETECTION CONDITIONS AND POSSIBLE CAUSES 



Start the engine and run it at idle.  



Retrieve DTCs using the M-MDS.  



Is the PENDING CODE for this DTC 
present?  

No

Go to the next step.

6

VERIFY AFTER REPAIR PROCEDURE  



Perform "AFTER REPAIR PROCEDURE". 
(See AFTER REPAIR PROCEDURE 
[MZI-3.7].)  



Are any DTC present?  

Yes

Go to the applicable DTC inspection. 
(See DTC TABLE [MZI-3.7].)

No

Troubleshooting completed.

DTC P0132

P0132: Front HO2S (RH) circuit high voltage

DTC P0138

P0138: Rear HO2S (RH) circuit high voltage

DTC P0152

P0152: Front HO2S (LH) circuit high voltage

DTC P0158

P0158: Rear HO2S (LH) circuit high voltage

DETECTION CONDITION 



The HO2S signals are monitored for an over voltage condition.  



The code is set when the HO2S signal voltage is 1.5 V or more.  

POSSIBLE CAUSE 



Short to power supply in the wiring harness or HO2S  

 

2008 Mazda CX-9 Grand Touring 

2008 ENGINE PERFORMANCE On-Board Diagnostic (MZI-3.7) - Mazda CX-9

  

Microsoft 

 

Sunday, November 15, 2009 10:08:35 AM

Page 83 

© 2005 Mitchell Repair Information Company, LLC. 

DIAGNOSTIC PROCEDURE 

DTC P0128 (MZI-3.7) DIAGNOSTIC PROCEDURE 

STEP

INSPECTION

ACTION

 

2008 Mazda CX-9 Grand Touring 

2008 ENGINE PERFORMANCE On-Board Diagnostic (MZI-3.7) - Mazda CX-9

  

Microsoft 

 

Sunday, November 15, 2009 10:08:35 AM

Page 84 

© 2005 Mitchell Repair Information Company, LLC.