Mazda MX-5 Miata (1997+). Manual - part 13

1997 AUTOMATIC TRANSMISSIONS

NC4A-EL Electronic Controls 

APPLICATION 

TRANSMISSION APPLICATION 

DESCRIPTION 

The NC4A-EL series is a 4-speed electronically controlled automatic transmission. Five solenoids attached to 
valve body control shift changes. Solenoids are controlled by the Transmission Control Module (TCM). 

The TCM receives information from various input devices. The TCM uses this information to control following 
solenoids:  



Shift solenoids for transmission shifting.  



Torque Converter Clutch (TCC) solenoid for torque converter clutch lock-up.  



3-2 control solenoid for downshift timing control.  

A HOLD switch is mounted on the shift lever. HOLD function may be activated in "D", "S" or "L" gears by 
pressing HOLD button. In "L" and "S" positions, vehicle is held in selected gear and no upshift or downshift 
takes place. This function is used for driving up steep inclines or for engine braking assistance when descending 
steep grades. If activated in "D" position a 1-2 and 2-3 upshift is permitted when starting from a stop, but after 
the 2-3 upshift the vehicle is locked in "D" until it comes to a complete stop. The 1-2 and 2-3 upshift pattern is 
changed to a "short shift" specification. This function is used for starting off or driving on slippery surfaces. 
Pushing HOLD button again deactivates system.

Vehicle

Transmission Model

Miata

NC4A-EL

CAUTION: Vehicle is equipped with Supplemental Restraint System (SRS). When 

servicing vehicle, use care to avoid accidental air bag deployment. SRS-
related components are located in steering column, center console and 
instrument panel. DO NOT use electrical test equipment on these circuits. 
If necessary, deactivate SRS before servicing components. See AIR BAG 
DEACTIVATION PROCEDURES article in GENERAL INFORMATION.

CAUTION: Disconnecting battery on models equipped with anti-theft radio require 

canceling of anti-theft operation. See appropriate AUTOMATIC 
TRANSMISSION SERVICING article in TRANSMISSION SERVICING. Refer 
to vehicle owner's manual to identify radio type.

NOTE:

Torque Converter Clutch (TCC) solenoid is also known as lock-up solenoid, 
TCC lock-up or 4th gear solenoid.

 

1997 Mazda MX-5 Miata 

1997 AUTOMATIC TRANSMISSIONS NC4A-EL Electronic Controls

  

 

1997 Mazda MX-5 Miata 

1997 AUTOMATIC TRANSMISSIONS NC4A-EL Electronic Controls

  

OPERATION 

TCM 

TCM receives information from various input devices and uses this information to control solenoids on 
transmission valve body for transmission shifting and torque converter clutch engagement. 

TCM automatically switches from NORMAL mode to POWER mode corresponding to driving condition in 
"D" range. Upshifts and downshifts are performed at a higher speed in POWER mode than in NORMAL mode. 

TCM contains a self-diagnostic system, which will store Diagnostic Trouble Codes (DTC) if a failure or 
problem exists in electronic control system. DTC can be retrieved to determine problem area. See SELF-
DIAGNOSTIC SYSTEM . TCM is located under left side of instrument panel, above fuse block. 

TCM INPUT DEVICES & SIGNALS 

4th Gear Inhibit Signal 

Signal is input to TCM when cruise control is on. Signal detects when difference between target speed and 
actual speed exceeds specification. 

HOLD Switch 

HOLD switch delivers input to TCM to indicate gears preferred by operator. Switch is located on shift lever 
handle. HOLD switch is canceled when ignition switch is turned off. 

Input/Turbine Speed Sensor 

Sensor is a magnetic pick-up type pulse generator that monitors input shaft speed. AC waveform is input to 
TCM by output speed sensor. Sensor is located on front of transmission, back of converter housing. 

Throttle Position (TP) Sensor 

TP sensor delivers an input signal to TCM indicating throttle valve position (opening). TP sensor is located on 
side of throttle body. 

Transmission Range Switch 

Transmission range switch delivers an input signal to TCM indicating shift lever position. Switch is located on 
side of transmission. 

Transmission Fluid Temperature (TFT) Sensor 

TFT sensor is threaded into cooler line banjo mounting on side of transmission case. Sensor sends signal to 
TCM indicating fluid temperature. 

Vehicle Speed Sensor 

 

1997 Mazda MX-5 Miata 

1997 AUTOMATIC TRANSMISSIONS NC4A-EL Electronic Controls

  

Sensor is a cable driven pulse generator that is part of speedometer. Pulse signals are sent to TCM.

TCM OUTPUT DEVICES 

HOLD Indicator Light 

Receives signal from TCM to indicate switch position. 

Inhibitor Signal 

When shift selector lever is moved from Park or Neutral to another gear, signal is sent from TCM to ECM to 
regulate fuel injection volume for shift shock prevention. 

Shift Solenoids & 3-2 Control Solenoid 

The TCM controls transmission shifting by delivering an output signal to operate proper solenoid. 3-2 control 
solenoid affects downshift timing. See SOLENOID OPERATION table. Hydraulic pressure is retained when 
solenoid is off and drained when solenoid is on. Solenoids are located on transmission valve body. See Fig. 1 . 

SOLENOID OPERATION 

TCC Solenoid Valve 

Solenoid valve is ON/OFF type controlled by TCM. Solenoid regulates pilot pressure to applied to lock-up 
control plug. Hydraulic pressure is retained when solenoid is on and drained when solenoid is off. Solenoid is 
located on side of case. See Fig. 1 . 

Shift Lever Position

1-2 Shift Solenoid 2-3 Shift Solenoid

3-4 Shift 

Solenoid

"D" (Drive)

1st Gear

On

On

On

2nd Gear

Off

On

On

3rd Gear

Off

Off

On

4th Gear

Off

Off

Off

"2" (Second)

1st Gear

On

On

On

2nd Gear

Off

On

On

"L" (Low)

1st Gear

On

On

On

"R" (Reverse)

Off

Off

On

"N" or "P"

On

On

On

 

1997 Mazda MX-5 Miata 

1997 AUTOMATIC TRANSMISSIONS NC4A-EL Electronic Controls

  

Fig. 1: Locating Solenoid Valves 
Courtesy of MAZDA MOTORS CORP. 

SELF-DIAGNOSTIC SYSTEM 

SYSTEM DIAGNOSIS 

TCM monitors transmission operation and contains a self-diagnostic system which stores a Diagnostic Trouble 
Code (DTC) if an electronic control system failure or component malfunction exists. If a problem exists in any 
of the solenoids or speed sensors and DTC is set, TCM will deliver a signal to blink the HOLD indicator light 
on instrument panel to warn the driver. DTC may be set if a failure exists and can be retrieved for transmission 
diagnosis. 

RETRIEVING TROUBLE CODES 

NOTE:

Before testing transmission, ensure fluid level is correct. Ensure engine starts 
with shift lever in Park and Neutral to ensure proper adjustment of transmission 
range switch. Transmission Control Module (TCM) must first be checked for 
stored codes. See RETRIEVING TROUBLE CODES .

NOTE:

Before retrieving DTC, ensure proper battery voltage exists for self-diagnostic 
system operation. If any DTC are present other than those listed below, see 

 

1997 Mazda MX-5 Miata 

1997 AUTOMATIC TRANSMISSIONS NC4A-EL Electronic Controls