P0120
DTC P0120THROTTLE POSITION SENSOR CIRCUIT MALFUNCTION (THV)
Description
- A Throttle Position Sensor is provided with a potentiometer which is interlocked with the Throttle Valve shaft.
- This Throttle Position Sensor sends the Engine Control Module (ECM) a potentiometer output signal corresponding to the opening of the Throttle Valve. When the level of this signal exceeds a predetermined value the ECM interprets it as complete closure of the Throttle Valve and makes a control most suitable for the Engine operation with the Throttle Valve fully closed. For correcting error of this signal the ECM is provided with a learning function.
- Thus, the ECM precisely controls the air-fuel ratio during acceleration and deceleration as well as Engine idling.
DTC Detecting Condition
Immediately at fault recognition.
Trouble Symptom
- Erroneous idling.
- Engine stalls.
- Poor driving performance
1. Connect Subaru Select Monotor or the OBD-II General Scan Tool, and read data.
a. Turn Ignition switch to "OFF".
b. Connect Subaru Select Monitor or the OBD-II General Scan Tool to Data Link Connector.
c. Turn Ignition switch to "ON" and Subaru Select Monitor or OBD-II General Scan Tool switch to "ON".
d. Start Engine.
e. Read data on Subaru Select Monitor or OBD-II General Scan Tool.
Subaru Select Monitor
- Designate mode using function key.
- Function mode: F10.
[CHECK]: Is the voltage less than 0.1 Volts?
[YES]: Go to step 2.
[NO]: Go to next [CHECK].
[CHECK]: Is the voltage more than 4.9 Volts?
[YES]: Go to step 4.
[NO]: Even it Malfunction Indicator Lamp (MIL) lights up, the circuit has returned to a normal condition at this time. A temporary poor contact of the connector may be the cause. Check and repair the following connectors.
- Throttle Position Sensor connector.
- ECM connector.
- Coupling connector (B21).
OBD-II General Scan Tool
- For detailed operation procedures, refer to the OBD-II General Scan Tool Instruction Manual.
2. Check input signal for ECM. (Using voltage meter and Subaru Select Monitor.)
a. Measure voltage between ECM and body while Throttle Valve is fully closed.
[CHECK]: Connector & terminal:
(B84) No. 22 - Body/4.5 Volts, or more.
[YES]: Go to next step.
[NO]: Go to next [CHECK].
[CHECK]: Is the voltage more than 4.5 Volts while shaking harness and connector of ECM?
[YES]: Repair poor contact in ECM connector.
[NO]: Replace ECM.
b. Measure signal voltage between ECM and body.
[CHECK]: Connector & terminal:
(B84) No. 24 - Body/0.1 Volts, or less.
[YES]: Go to next [CHECK].
[NO]: Go to step 3.
[CHECK]: Is the voltage more than 0.1 Volts while shaking harness and connector of ECM and monitoring the value with Subaru Select Monitor?
[YES]: Repair poor contact in ECM connector.
[NO]: Go to step 3.
3. Check harness connector between ECM and Throttle Position Sensor.
a. Turn Ignition switch to "OFF".
b. Disconnect connectors from Throttle Position Sensor.
c. Turn Ignition switch to "ON".
d. Measure voltage between Throttle Position Sensor connector and body.
[CHECK]: Connector & terminal:
(E13) No. 3 - Body/4.5 Volts, or more.
[NO]: Repair harness and connector.
NOTE: In this case, the possible causes are:
- Open circuit of the harness between connector (E13) terminal No. 3 and connector (B84) terminal No. 22, or the following:
- Poor contact in Throttle Position Sensor connector.
- Poor contact in ECM connector.
- Poor contact in coupling connector (B21)
[YES]: Go to the next step.
e. Turn Ignition switch to "OFF".
f. Measure resistance of harness between ECM connector and Throttle Position Sensor connector.
[CHECK]: Connector & terminal:
(B84) No. 24 - (E13) No. 2/10 Ohms, or less.
[NO]: Repair harness and connector.
NOTE: In this case, the following are the possible causes.
- Open circuit between connector (B84) terminal No. 24 and connector (E13) terminal No. 2.
- Poor contact in ECM connector.
- Poor contact in Throttle Position Sensor connector.
- Poor contact in coupling connector (B21).
[YES]: Go to next step.
g. Measure resistance of harness between Throttle Position Sensor connector and body.
[CHECK]: Connector & terminal:
(E13) No. 2 - Body/10 Ohms, or less.
[YES]: Repair short circuit of harness between Throttle Position Sensor and ECM connector.
[NO]: Go to next [CHECK].
[CHECK]: Is there poor contact in Throttle Position Sensor connector?
[YES]: Repair poor contact in Throttle Position Sensor connector.
[NO]: Replace Throttle Position Sensor.
4. Check harness connector between Throttle Position sensor and body.
a. Turn Ignition switch to "OFF".
b. Disconnect connector from Throttle Position Sensor.
c. Measure resistance of harness between Throttle Position Sensor connector and body.
[CHECK]: Connector & terminal:
(E13) No. 1 - Body/1O Ohms, or less.
[NO]: Repair open circuit of harness between Throttle Position Sensor and ECM connector.
[NO]: Go to the next step.
d. Turn Ignition switch to "ON".
e. Measure voltage between Throttle Position Sensor connector and body.
[CHECK]: Connector & terminal:
(E13) No. 2 - Body/4.9 Volts, or more.
[YES]: Repair short circuit of harness between Throttle Position Sensor and ECM connector.
[NO]: Replace Throttle Position Sensor.