Mazda MX-5 Miata / Grand Touring. Manual - part 95

CIRCUIT OPEN/SHORT INSPECTION

1. Disconnect the PCM connector. (See PCM REMOVAL/INSTALLATION [LF] .)  

2. Inspect the following wiring harnesses for open or short circuit (continuity check).  

Open Circuit 



If there is no continuity, there is an open circuit. Repair or replace the wiring harness. 



EGR valve terminal A and PCM terminal 2G  



EGR valve terminal B and PCM terminal 2L  



EGR valve terminal E and PCM terminal 2K  



EGR valve terminal F and PCM terminal 2H  



EGR valve terminal C and main relay  



EGR valve terminal D and main relay  

Short Circuit 



If there is continuity, there is a short circuit. Repair or replace the wiring harness. 



EGR valve terminal A and body ground  



EGR valve terminal A and power supply  



EGR valve terminal B and body ground  



EGR valve terminal B and power supply  



EGR valve terminal C and body ground  



EGR valve terminal D and body ground  



EGR valve terminal E and body ground  



EGR valve terminal E and power supply  



EGR valve terminal F and body ground  



EGR valve terminal F and power supply 

 

2008 Mazda MX-5 Miata Grand Touring 

2008 ENGINE PERFORMANCE Emission System - MX-5 Miata

  

Fig. 29: Identifying EGR Valve & PCM Wiring Harness-Side Connector 
Courtesy of MAZDA MOTORS CORP. 

POSITIVE CRANKCASE VENTILATION (PCV) VALVE INSPECTION [LF] 

1. Remove the intake manifold. (See INTAKE-AIR SYSTEM REMOVAL/INSTALLATION [LF] .)  

2. Remove the PCV valve.  

3. Verify that there is no airflow when pressure is applied to port A. 



If there is airflow, replace the PCV valve.  

4. Verify that there is airflow when vacuum is applied to port A. 

 

2008 Mazda MX-5 Miata Grand Touring 

2008 ENGINE PERFORMANCE Emission System - MX-5 Miata

  



If there is no airflow, replace the PCV valve.  

Fig. 30: Identifying PCV Valve 
Courtesy of MAZDA MOTORS CORP. 

WARM-UP THREE-WAY CATALYTIC CONVERTER (WU-TWC) INSPECTION 
[LF] 

1. Connect the M-MDS or equivalent and monitor PIDs as following. 



Monitor the WU-TWC using O2S11 PID for upstream HO2S and O2S12 PID for downstream 
HO2S.  

NOTE:



Make sure that no HO2S DTCs have been detected. If detected, this 
inspection is not applicable for WU-TWC inspection.  

 

2008 Mazda MX-5 Miata Grand Touring 

2008 ENGINE PERFORMANCE Emission System - MX-5 Miata

  

2. Monitor the appropriate PIDs.  

3. Drive the vehicle for 10 min at 65-96 km/h {40-60 mph} to allow the front catalytic converter to reach 

operating temperature.  

4. Stop the vehicle and leave it in a safe place.  

5. Idle the engine.  

6. Record PIDs for 1 min .  

7. Select the appropriate PIDs and read the graph.  

8. Count the number of times (inversions) that the upstream HO2S graph line actually crosses the 0.5 V line. 

Fig. 31: Identifying HO2S Graph Line (5 Inversions) 
Courtesy of MAZDA MOTORS CORP. 

9. Count the number of times (inversions) that the downstream HO2S graph line actually crosses the 0.5 V 

line. 

10. Using the following equation, calculate the value of ratio. 

Equation  

RATIO = Upstream HO2S inversion divided by downstream HO2S inversion  

NOTE:



Do not count the number of peaks. Refer to Fig. 31 . 

 

2008 Mazda MX-5 Miata Grand Touring 

2008 ENGINE PERFORMANCE Emission System - MX-5 Miata