DTC 123

EAG. Code 1-2-3

1-2-3 Short-circuit to battery voltage in solenoid STH circuit
DTC information


Conditions for DTC






Solenoid STH controls the transmission system pressure The solenoid is controlled by an integral amplifier (driver stage) on the output of the transmission control module (TCM). The TOM uses the driver stage to regulate the current supplied to the solenoid. A low amperage gives a high system pressure and a high amperage (approx. 1A) gives a low system pressure. The amperage of this current is affected primarily by the throttle position. If the TCM registers a short circuit to battery voltage on the solenoid STH circuit so that the amperage is too high in the circuit, DTC 1-2-3 is set. Solenoid STH is unable to control the system pressure.

Substitution value

The TCM "Limp-home" program has been initiated and the transmission operates only in 4th gear.

Defect cause

- Short circuit to battery voltage in the control signal wiring or signal wiring.
- Short circuit between the control signal wiring and signal wiring.
- Malfunction in solenoid STH.

Fault symptom

- Poor performance due to the transmission operating only in 4th gear.

NOTE: This fault indicates a risk that system pressure may be too low, which will result in increased wear.

- Fault-tracing starts with EAG1.








EAG1

Checking solenoid STH






- Ignition ON.
- Set gearshift selector to position P.

Check solenoid STH using Diagnostic Test Mode 4. Use a stethoscope to hear if the solenoid is operating.


NOTE: The solenoid only clicks twice - when stopping and when starting. So listen carefully.


If solenoid is operating
- Intermittent fault. Fault-tracing as per EAG8.

If the solenoid is not operating:
- Checking resistance in solenoid STH circuit EAG2.



EAG2

Checking resistance in solenoid STH circuit






- Ignition OFF
- Connect test box and check ground points as per GB1-GB2 GB. Connecting the Test Box
- TCM disconnected.

Use an ohmmeter to measure between #22 (#A22) and #23 (#A23) on the test box.

The ohmmeter should read 2-6 Ohms.

If reading is OK:
- Check short circuit to battery voltage in the control signal wiring EAG5.

If reading is incorrect:
- Check solenoid STH circuit in the transmission EAG3.




EAG3

Checking solenoid STH circuit in the transmission







- Ignition OFF
- Remove the air cleaner (AC) housing to access the transmission connector
- Disconnect the transmission connector.

Connect an ohmmeter between the transmission connector terminals 24 and 25 (transmission side).

The ohmmeter should read 2-6 Ohms.

If reading is OK:
- Check the wiring between the transmission connector terminal 24 and 25 and the TCM #A22 and #A23 for short circuit between the cables.
Then continue with: Checking the control module EAG7.

If reading is incorrect
- Checking resistance in solenoid STH EAG4.



EAG4

Checking resistance in solenoid STH







- Ignition OFF
- Open the control system, as per R1-R13.
- Disconnect solenoid STH.

Connect ohmmeter between the pins in the solenoid connector.
The ohmmeter should read 2-6 Ohms.

If reading is OK:
- Check the wiring between solenoid STH and the transmission connector terminals 24 and 25 for short circuit between the cables.
Then continue with: Checking the control module EAG7.

If reading is incorrect:
- Replace transmission control system as per R1-R14.
Then continue with: Checking the control module EAG7.




EAG5

Checking in the control signal wiring for short circuit to battery voltage






- Ignition OFF
- Test box connected
- Connect TCM
- Ignition ON.

Use a voltmeter to measure between #22 (#A22) and #20 (#A20) on the test box.
The voltmeter should register 0-6 V.

If reading is OK:
- Checking control signal wiring for short circuit to battery voltage EAG6.

If reading is incorrect:
- Check wiring between solenoid STH and TCM #A22 for short circuit to supply as per FA4. FA. Checking Wiring and Connections
Then continue with: Checking the control module EAG7.



EAG6

Checking signal wiring for short circuit to battery voltage







- Ignition ON.

Use a voltmeter to measure between #23 (#A23) and #20 (#A20) on the test box.

The voltmeter should register 0-2 V.

If reading is OK:
- Checking the control module EAG7.

If reading is incorrect:
- Check wiring between solenoid STH and TCM #A23 for short circuit to battery voltage.
Then continue with: Checking the control module EAG7.



EAG7

Checking the transmission control module TCM







The transmission control module (TCM) can malfunction due to a short circuit to battery voltage in the solenoid STH circuit. Check the TCM as follows:

- Ignition OFF
- Reinstall connector and air cleaner AC.
- Ignition ON.
- Clear DTCs
- Test drive the car at a road speed over 25 km/h (15 mph).

If the DTC does not recur:
- Checking system pressure EAG9.

If the DTC is set again:
- Try a new TCM as per AB1-AB4.

NOTE: It is important that the solenoid STH circuit is not short-circuited to battery voltage. A short-circuit on the circuit can damage the new TCM.



EAG8

Intermittent Fault.

Checking wiring and connections






Check the wiring between solenoid STH and TCM #A27 and #A23 for intermittent short-circuit to supply as per FA4, and for intermittent short-circuit between the cables. FA. Checking Wiring and Connections
Then continue with: Checking system pressure EAG9.



EAG9

Checking system pressure.






Diagnostic Trouble Code (DTC) 1-2-3 indicates a risk that transmission system pressure may be too low, which will result in increased wear. Always check the transmission system pressure.

Check system pressure as per K1-K4.

If system pressure is OK:
- Test run on the transmission EAG11

If system pressure is incorrect:
- Checking TCM operation EAG1O.


EAG1O

Checking TCM operation






- Ignition OFF
- Disconnect the old TCM and install a new control module
- Recheck system pressure as per K1-K4.

If system pressure is OK:
- The old TCM is detective.

If system pressure is still incorrect:

- Ignition OFF
- Reinstall the old TCM
- Test drive the transmission as per Test Drive Form in order to detect other symptoms. See diagnostic code 1-1-1 for symptoms and procedures. DTC 111



EAG11

Test run on the transmission






- Make the car ready for test driving:
- Test drive the car as per Test Drive Form. Test Aide Drive Form

Pay attention to transmission performance during test drive.

If no mechanical fault symptoms occur:
- The transmission is operating correctly.

If mechanical fault symptoms occur:
- Try a new transmission as per U1-U65.