P0123-THROTTLE POSITION SENSOR 1 CIRCUIT HIGH





For a complete wiring diagram Refer to Section 8W.



Possible Causes
(K22) TP SIGNAL 1 CIRCUIT SHORTED TO BATTERY VOLTAGE
(K22) TP SIGNAL 1 CIRCUIT OPEN
(K22) TP SIGNAL 1 CIRCUIT SHORTED TO THE (F855) 5-VOLT SUPPLY CIRCUIT
(K922) TP RETURN CIRCUIT OPEN
THROTTLE POSITION SENSOR/THROTTLE BODY
THROTTLE PLATE JAMMED AGAINST THE MAXIMUM STOP
PCM

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).



Diagnostic Test

1. TP SENSOR NO.1 VOLTAGE ABOVE 4.8 VOLTS

NOTE: When this DTC is Active the engine speed, torque, and vehicle speed are limited to a Limp in mode.

NOTE: Make sure the throttle is fully closed and free from binding or carbon build up.

NOTE: If a 5-Volt Supply DTC has also set, diagnose the 5-Volt DTC before continuing.

NOTE: If P2101 is also set, then make sure that the blade moves freely and does not hang up near Wide Open Throttle before trying to repair P0123.


Start the engine.
With a scan tool, read the TP Sensor No.1 voltage.

Is the voltage above 4.8 volts?

Yes


No

2. THROTTLE POSITION SENSOR



Turn the ignition off.
Disconnect the Throttle Body harness connector.
Connect a jumper wire between the (K22) TP Signal 1 circuit and the (K922) TP Return circuit in the Throttle Body harness connector.
With a scan tool, monitor the TP Sensor No.1 voltage.
Ignition on, engine not running.

Is the voltage below 0.5 of a volt with the jumper wire installed?

Yes


No

3. (K22) TP SIGNAL 1 CIRCUIT SHORTED TO BATTERY VOLTAGE



Turn the ignition off.
Disconnect the C2 PCM harness connector.
Ignition on, engine not running.
Measure the voltage on the (K22) TP Signal 1 circuit in the Throttle Body harness connector.

Is the voltage above 0 volts?

Yes


No

4. (K22) TP SIGNAL 1 CIRCUIT OPEN



Turn the ignition off.

CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool #8815 to perform diagnosis.


Measure the resistance of the (K22) TP Signal 1 circuit from the Throttle Body harness connector to the appropriate terminal of special tool #8815.

Is the resistance below 5.0 ohms?

Yes


No

5. (K22) TP SIGNAL 1 CIRCUIT SHORTED TO THE (F855) 5-VOLT SUPPLY CIRCUIT



Measure the resistance between the (K22) TP Signal 1 circuit and the (F855) 5-volt Supply circuit in the Throttle Body harness connector.

Is the resistance below 100 ohms?

Yes


No

6. (K922) TP RETURN CIRCUIT OPEN



Measure the resistance of the (K922) TP Return circuit from the Throttle Body harness connector to the appropriate terminal of special tool #8815.

Is the resistance below 5.0 ohms?

Yes


No

7. PCM

NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.


Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and Ground circuits.

Were there any problems found?

Yes


No

8. THROTTLE FOLLOWER TEST

With a scan tool, perform the Throttle Follower Test.
Monitor the TP Sensor No.1 voltage.

Does voltage start at approximately 0.3 of a volt and go above 4.7 volts with a smooth transition?

Yes


No