Mazda MX-5 Miata (1997+). Manual - part 17



Shift solenoid malfunction.  

Diagnosis & Repair Procedure 

1. Ensure all connections are clean and tight. Repair as needed. Turn ignition on. Access TCM connectors. 

Using voltmeter, backprobe harness connectors. DO NOT disconnect connectors. Go to next step.  

2. Measure voltage between ground and terminal No. 2G (Orange wire) on TCM connector. During test 

drive, voltage should be less than one volt when solenoid is off and battery voltage when solenoid is on. 
See SOLENOID OPERATION table under TCM OUTPUT DEVICES. If voltage is within 
specification, go to step 5 . If voltage is not within specification, go to next step.  

3. Turn ignition off. Disconnect TCM harness connector. Measure resistance between ground and terminal 

No. 2G. If resistance is 13-27 ohms at 68°F (20°C), go to step 5 . If resistance is not 13-27 ohms at 68°F 
(20°C), go to next step.  

4. Inspect 2-3 shift solenoid and related circuits. See SOLENOID VALVES under COMPONENT 

TESTING. Repair as needed. If solenoid valve and related circuits are okay, go to next step.  

5. Clear trouble codes and road test vehicle. Retrieve DTC. If DTC P0755 is still present, replace TCM. If 

code is no longer present, system is okay.  

DTC P0760: 3-4 SHIFT SOLENOID MALFUNCTION 

Possible Causes: 



Short or open circuit between TCM and solenoid.  



TCM malfunction.  



Shift solenoid malfunction.  

Diagnosis & Repair Procedure 

1. Ensure all connections are clean and tight. Repair as needed. Turn ignition on. Access TCM connectors. 

Using voltmeter, backprobe harness connectors. DO NOT disconnect connectors. Go to next step.  

2. Measure voltage between ground and terminal No. 2I (Blue wire) on TCM connector. During test drive, 

voltage should be less than one volt when solenoid is off and battery voltage when solenoid is on. See 
SOLENOID OPERATION table under TCM OUTPUT DEVICES. If voltage is within specification, go 
to step 5 . If voltage is not within specification, go to next step.  

3. Turn ignition off. Disconnect TCM harness connector. Measure resistance between ground and terminal 

No. 2E. If resistance is 13-27 ohms at 68°F (20°C), go to step 5 . If resistance is not 13-27 ohms at 68°F 
(20°C), go to next step.  

4. Inspect 3-4 shift solenoid and related circuits. See SOLENOID VALVES under COMPONENT 

TESTING. Repair as needed. If solenoid valve and related circuits are okay, go to next step.  

5. Clear codes and road test vehicle. Retrieve DTC. If DTC P0760 is still present, replace TCM. If code is 

no longer present, problem is intermittent. Further investigation may be necessary.  

DTC P1720: VEHICLE SPEED SENSOR SIGNAL MISSING 

 

1997 Mazda MX-5 Miata 

1997 AUTOMATIC TRANSMISSIONS NC4A-EL Electronic Controls

  

Condition 

Vehicle speed sensor signal is not input to TCM. Possible causes are: 



Vehicle speed sensor malfunction.  



Vehicle speedometer sensor malfunction.  



Damaged circuits or connectors between sensors and TCM.  

Diagnosis & Repair Procedure 

1. Ensure all connections are clean and tight. Repair as needed. Turn ignition on. Using voltmeter, 

backprobe TCM harness connector. DO NOT disconnect connector. Test drive vehicle.  

2. Measure voltage between ground and terminal No. 1P (Green/Red wire) on TCM harness connector. 

During test drive voltage should be about 4 volts. When parked, voltage should be less than 1.5 or 7-9 
volts. If voltage is within specifications, go to step 5 . If voltage is not within specifications, go to next 
step.  

3. Turn ignition off. Disconnect negative battery cable. Remove instrument cluster. Disconnect TCM 

harness connectors. Ensure continuity exists on Green/Red wire between terminal No. 1P on TCM 
connector and terminal No. 2F on instrument cluster harness left connector. Repair as needed. If 
continuity exists, go to next step.  

4. With combination meter removed, measure voltage between terminals No. 2F and 2D on combination 

meter connector using analog voltmeter. Raise and support vehicle. Rotate rear wheels. If voltage pulse is 
present, go to next step. If voltage pulse is not present, inspect speedometer cable. Replace as needed. If 
cable is okay, replace combination meter or circuit board (as applicable).  

5. Clear codes and road test vehicle. Retrieve DTC. If DTC 1720 is still present, replace TCM. If code is no 

longer present, problem may be caused by poor connection. Repair as needed.  

DTC P1743: TORQUE CONVERTER CLUTCH (TCC) SOLENOID MALFUNCTION 

Possible Causes: 



Short or open circuit between TCM and solenoid.  



TCM malfunction.  



Lock-up solenoid malfunction.  

Diagnosis & Repair Procedure 

1. Ensure all connections are clean and tight. Repair as needed. Turn ignition on. Access TCM connectors. 

Using voltmeter, backprobe harness connectors. DO NOT disconnect connectors. Go to next step.  

2. Measure voltage between ground and terminal No. 2K (Yellow/Black wire). Battery voltage should be 

present with solenoid on and zero volts with solenoid off. If voltage is within specifications, go to step 5 . 
If voltage is not within specifications, go to next step.  

3. Turn ignition off. Disconnect TCM harness connector. Measure resistance between ground and terminal 

No. 2K. If resistance is 13-25 ohms at 68°F (20°C), go to step 5 . If resistance is not 13-25 ohms at 68°F 
(20°C), go to next step.  

 

1997 Mazda MX-5 Miata 

1997 AUTOMATIC TRANSMISSIONS NC4A-EL Electronic Controls

  

4. Inspect lock-up solenoid and related circuits. See SOLENOID VALVES under COMPONENT 

TESTING. Repair as needed. If solenoid valve and related circuits are okay, go to next step.  

5. Clear codes and road test vehicle. Retrieve DTC. If DTC P1743 is still present, replace TCM. If code is 

no longer present, problem may be caused by poor connection. Repair as needed.  

DTC P1765: 3-2 CONTROL SOLENOID VALVE MALFUNCTION 

Possible Causes: 



Short or open circuit between TCM and solenoid.  



TCM malfunction.  



3-2 control solenoid malfunction.  

Diagnosis & Repair Procedure 

1. Ensure all connections are clean and tight. Repair as needed. Turn ignition on. Access TCM connectors. 

Using voltmeter, backprobe harness connectors. DO NOT disconnect connectors. Go to next step.  

2. Drive vehicle and measure voltage between ground and terminal No. 2M (Blue/Orange wire). Battery 

voltage should be present with solenoid on during 3-2 or 4-3 downshift, and zero volts with solenoid off. 
If voltage is within specifications, go to step 5 . If voltage is not within specifications, go to next step.  

3. Turn ignition off. Disconnect TCM harness connector. Measure resistance between ground and terminal 

No. 2M. If resistance is 13-27 ohms at 68°F (20°C), go to step 5 . If resistance is not 13-27 ohms at 68°F 
(20°C), go to next step.  

4. Inspect 3-2 control clutch solenoid and related circuits. See SOLENOID VALVES under 

COMPONENT TESTING. Repair as needed. If solenoid valve and related circuits are okay, go to next 
step.  

5. Clear codes and road test vehicle. Retrieve DTC. If DTC P1765 is still present, replace TCM. If code is 

no longer present, problem may be caused by poor connection. Repair as needed.  

DTC P1790: THROTTLE POSITION (TP) SENSOR MALFUNCTION 

Condition 

TP sensor voltage is less than one volt or more than 4.9 volts. Possible causes are: 



Poor harness connection at TP sensor.  



Circuit fault between TP sensor and ECM or TCM.  



TP sensor malfunction.  



ECM or TCM malfunction.  

Diagnosis & Repair Procedure 

NOTE:

If DTC P0725 is also present, repair it first and then proceed with this test.

 

1997 Mazda MX-5 Miata 

1997 AUTOMATIC TRANSMISSIONS NC4A-EL Electronic Controls

  

1. Ensure all connections are clean and tight. Repair as needed. Ensure that TP sensor is adjusted correctly. 

See appropriate ON-VEHICLE ADJUSTMENTS article in ENGINE PERFORMANCE. Turn ignition 
on. Access TCM connectors. Using voltmeter, backprobe harness connectors. DO NOT disconnect 
connectors. Go to next step.  

2. Measure voltage between ground and terminal No. 2T (Red/Black wire) on TCM harness connector. With 

throttle closed, voltage should be .1-1.1 volts. With wide open throttle, voltage should be 3.1-4.4 volts. If 
voltage is within specification, go to step 5 . If voltage is not within specification, go to next step.  

3. Measure voltage between ground and terminal No. 2A (Light Green/White wire) on TCM harness 

connector. With ignition on, voltage should be 4.5-5.5 volts. With ignition off, voltage should be zero 
volts. If voltage is within specification, go to step 5 . If voltage is not within specification, go to next step. 

4. Inspect circuits between TP sensor and TCM. See appropriate wiring diagram under WIRING 

DIAGRAMS . Repair as needed. If circuits are okay between sensor and TCM, go to next step.  

5. Clear codes, and road test vehicle. Retrieve DTC. If DTC P1790 is still present, replace TCM. If code is 

no longer present, system is okay.  

DTC P1795: IDLE SWITCH OPEN OR SHORT 

Condition 

Closed throttle position switch is ON and TP sensor position is closed. Possible causes are:  



Damaged wiring or connectors between closed throttle position switch and TCM.  



Closed throttle position switch malfunction.  



TCM malfunction.  

Diagnosis & Repair Procedure 

1. Ensure all connections are clean and tight. Repair as needed. Turn ignition on. Access TCM connectors. 

Using voltmeter, backprobe harness connectors. DO NOT disconnect connectors. Go to next step.  

2. Measure voltage between ground and terminal No. 1O (Red wire) on TCM harness connector. With 

throttle closed, battery voltage should be present. With wide open throttle, voltage should be zero volts. If 
voltage is within specification, go to step 5 . If voltage is not within specification, go to next step.  

3. Inspect circuits between closed throttle position switch and TCM. See appropriate wiring diagram under 

WIRING DIAGRAMS . Repair as needed. If circuits are okay between sensor and TCM, go to next 
step.  

4. Disconnect battery negative cable. Disconnect closed throttle position switch connector. Check for 

continuity between closed throttle position switch terminals. If continuity exists, go to next step. If 
continuity does not exist, replace or adjust throttle position sensor.  

5. Clear codes, and road test vehicle. Retrieve DTC. If DTC P1795 is still present, replace TCM. If code is 

no longer present, problem is intermittent. Further investigation is required.  

COMPONENT TESTING 

NOTE:

For connector terminal identification, see COMPONENT CONNECTOR 

 

1997 Mazda MX-5 Miata 

1997 AUTOMATIC TRANSMISSIONS NC4A-EL Electronic Controls