DTC 123

DG. DTC 1-2-3
1-2-3 Short-circuit to supply in solenoid STH circuit

Principle of operation

Solenoid STH controls the transmission fluid pressure. Low fluid pressure may result if the solenoid becomes damaged, causing considerable wear. Driving the car for a prolonged period in this condition may necessitate replacement of the transmission.

The solenoid is operated by a variable current from the TCM, the value of which is influenced primarily by the throttle. The pressure is low at high current levels (approx. 1 A). The line pressure is a maximum at low currents or when the current is interrupted.

Fault description

Short-circuit to supply in solenoid STH circuit. Transmission fluid pressure insufficient. The emergency limp-home program is activated and the transmission operates only in 4th gear. The MIL on the panel lights.





Circuit description

The circuit consists of the TCM, connectors and solenoid STH in the transmission.





1
Testing solenoid STH in test mode 4

- Move gear selector lever to position P. Test solenoid STH in test mode 4. Displaying & Reading Trouble Codes

Note!
Since solenoid clicks only twice (on and off operation), listen carefully with stethoscope for sound.

- If solenoid does not click, fault is permanent.
- If solenoid clicks, Fault is occurring only intermittently under particular conditions, making it considerably more difficult to locate.

Fault is probably short-circuit between leads in either case.





2
Measuring voltage with TCM in circuit

- Switch off ignition.
- Connect break-out box to wiring.
- Switch on ignition.

Measure voltage across # 3 (STH) and # 12 (SG), and between # 4 (STHG) and # 12.

- If instrument indicates battery voltage in either case, short-circuit is present between lead and other live lead. Check wiring and connections between TCM and solenoid STH as described in Testing and Inspection. Component Tests and General Diagnostics






3
Checking/test driving

- Erase DTCs.
- Check for wear (mechanical testing).

Test drive in all gears and operate all other functions, such as lights, radio, horn, cruise control etc.

- If fault returns after each test drive, fault may still be present or TCM may be faulty.

4
Checking line pressure

Always check line pressure when DTC 1-2-3 is displayed.

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