Transmission Control Systems

TROUBLE CODE 21
ATF TEMPERATURE SENSOR

Diagnosis
Input signal circuit of Transmission Control Module (TCM) to Automatic Transmission Fluid (ATF) Temperature Sensor is open or shorted.

Trouble Symptom
Excessive shift shock.











1. Check harness and connectors between TCM and ATF Temperature Sensor.
a. Turn Ignition Switch to "OFF".
b. Disconnect connectors from TCM and Transmission.





c. Measure resistance of harness connector between TCM and Transmission connector.
Connector & Terminal / Specified voltage:
(B54) No. 10 - (B11) No. 5 / 1 Ohm, or less.
(B56) No. 20 - (B11) No. 12 / 1 Ohm, or less.





d. Measure resistance of harness connector between TCM and body to make sure that circuit does not short.
Connector & Terminal / Specified Resistance:
(B54) No. 10 - Body / 1 M-Ohms, or more.
(B56) No. 20 - Body / 1 M-Ohms, or more.

2. Check ATF Temperature Sensor.





a. Measure resistance between Transmission connector receptacle's terminals.
Connector & Terminal / Specified Resistance:
(T4) No. 5 - No. 12 / 2.1 - 2.9 k-Ohms [ATF temperature: 20°C (68°F)].

b. Connect connectors to Transmission and TCM.
c. Start and warm-up the Engine until ATF temperature has increased.
d. Stop the Engine and disconnect connector from Transmission.
e. Measure resistance between Transmission connector receptacle's terminals.
Connector & Terminal / Specified Resistance:
(T4) No. 5 - No. 12 / 275 - 375 Ohms [ATF temperature: 80°C (176°F)].

3. Check input signal for TCM.
a. Turn Ignition Switch "ON" (with Engine OFF) and measure signal voltage input of TCM.





b. Start and warm-up the Engine. Measure signal voltage input of TCM.
Connector & Terminal / Specified voltage:
(B54) No. 10 - (B56) No. 20 /
3.45 ± 0.55 Volts [ATF temperature: 20°C (68°F)].
1.2 ± 0.2 Volts [ATF temperature: 80°C (176°F)].

Using Subaru Select Monitor





1. Turn Ignition Switch to "OFF".
2. Connect the Subaru Select Monitor to Data Link Connector.
3. Turn Ignition Switch to "ON" and Subaru Select Monitor switch to "ON".
4. Start and warm-up the Engine.
5. Read data on Subaru Select Monitor.
6. Designate mode using function key.
Function mode: F07 or FO8.

Specified Data:
F07: Ambient temperature: ± 50 deg F.
ATF temperature: 158 - 230 deg F.
Open harness: 176 deg F.
Shorted harness: 320 deg F.
F08: Ambient temperature: ± 10 deg C.
ATF temperature: 70 - 110 deg C.
Open harness: 80 deg C.
Shorted harness: 160 deg C.