Throttle light on and P0121 code

Hi,

The code is related to the throttle position sensor (high voltage). Is that the only code that is present? The cause could be the throttle body itself, a short in the wiring, or even the PCM.

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I noted that you are comfortable with working on vehicles by the heading. Take a look through these diagnostics and let me know if it something you are comfortable doing:

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1. CHECK FOR AN ACTIVE DTC

NOTE: When this DTC is active the engine speed, torque and vehicle speed are limited.
NOTE: Diagnose and repair any Throttle Body circuit, system voltage or 5-Volt Reference DTCs before continuing with this test.
NOTE: If P2101 is also set, make sure that the throttle plate moves freely and does not hang up near Wide Open Throttle before trying to repair P0121.
Start the engine and allow it to idle.
With the scan tool, read DTCs and record on the repair order.

Is the DTC active or pending?

Yes
Go To 2

No
Perform the INTERMITTENT CONDITION diagnostic procedure. (Refer to 28 - DTC-Based Diagnostics/MODULE, Power-train Control (PCM) - Standard Procedure).

2. THROTTLE FOLLOWER TEST

Turn the ignition on.
With the scan tool, perform the ETC Throttle Follower Test and monitor the TPS 1 voltage.
Slowly press the accelerator pedal down.

NOTE: The voltage for TPS 1 should start at approximately 0.7 volts and increase to approximately 4.3 volts.

Is the TPS 1 voltage within the range of the listed specification?

Yes
Go To 6

No
Go To 3

3. CHECK THE 5-VOLT SUPPLY CIRCUIT VOLTAGE

Turn the ignition off.
Disconnect the Throttle Body harness connector.
Turn the ignition on.
Measure the voltage on the (F855) 5-Volt Supply circuit in the Throttle Body harness connector.

Is the voltage between 4.8 and 5.2 volts?

Yes
Go To 4

No
Repair the (F855) 5-Volt Supply circuit for an open or short circuit.
Perform the POWER-TRAIN VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/module, Power-train Control (PCM) - Standard Procedure).

4. CHECK THE TPS SENSOR GROUND CIRCUIT FOR AN OPEN/HIGH RESISTANCE

Turn the ignition off.
Disconnect the PCM C2 harness connector.

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 the GPEC Diagnostic Adapter to perform the diagnosis.

Connect the Adapter, GPEC Diagnostic 10436.
Measure the resistance of the (K922) TPS 1 Sensor Ground circuit between the Throttle Body harness connector and the GPEC Adapter.

Is the resistance below 3.0 Ohms?

Yes
Go To 5

No
Repair the (K922) TPS 1 Sensor Ground circuit for an open or high resistance.
Perform the POWER-TRAIN VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Power-train Control (PCM) - Standard Procedure).

5. CHECK THE TPS 1 SIGNAL CIRCUIT FOR AN OPEN/HIGH RESISTANCE

Measure the resistance of the (K22) TPS 1 Signal circuit between the Throttle Body harness connector and the GPEC Adapter.

Is the resistance below 3.0 Ohms?

Yes
Go To 6

No
Repair the (K22) TPS 1 Signal circuit for an open or high resistance.
Perform the POWER-TRAIN VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/module, Power-train Control (PCM) - Standard Procedure).

6. THROTTLE POSITION SENSOR 1

Reconnect the PCM C2 harness connector if necessary.
Reconnect the Throttle Body harness connector.
Turn the ignition on.
With the scan tool, monitor the TPS 1 voltage.
Connect a jumper between the (K22) TPS 1 Signal circuit and the (K922) TPS Return circuit.

NOTE: The TPS 1 voltage should change from approximately 5.0 volts with the connector unplugged to 0.0 volts with the jumper in place.

Is the voltage reading within the listed specification when the jumper is installed?

Yes
Verify that there is good pin to terminal contact in the Throttle Body and Power-train Control Module connectors. If no problems are found, replace the Throttle Body Assembly. (Refer to 14 - Fuel System/Fuel Injection/THROTTLE BODY - Removal). Disconnect the Battery when replacing the Throttle Body Assembly. After installation is complete, use a scan tool and select the ETC RELEARN function.
Perform the POWER-TRAIN VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Power-train Control (PCM) - Standard Procedure).

No
Remove the jumper before continuing.
Go To 7

7. CHECK RELATED PCM AND COMPONENT CONNECTIONS

Perform any Service Bulletins that apply.
Disconnect all PCM harness connectors.
Disconnect all related in-line harness connections (if equipped).
Disconnect the related component harness connectors.
Inspect harness connectors, component connectors, and all male and female terminals for the following conditions:
Proper connector installation.
Damaged connector locks.
Corrosion.
Other signs of water intrusion.
Weather seal damage (if equipped).
Bent terminals.
Overheating due to a poor connection (terminal may be discolored due to excessive current draw).
Terminals that have been pushed back into the connector cavity.
Check for spread terminals and verify proper terminal tension.
Repair any conditions that are found.
Reconnect all PCM harness connectors. Be certain that all harness connectors are fully seated and the connector locks are fully engaged.
Reconnect all in-line harness connectors (if equipped). Be certain that all connectors are fully seated and the connector locks are fully engaged.
Reconnect all related component harness connectors. Be certain that all connectors are fully seated and the connector locks are fully engaged.
With the scan tool, erase DTCs.
Test drive or operate the vehicle in accordance with the when monitored and set conditions.
With the scan tool, read DTCs.

Did the DTC return?

Yes
Replace the Power-train Control Module in accordance with the Service information. (Refer to 08 - Electrical/8E - Electronic Control Modules/MODULE, Power-train Control - Removal).
Perform the POWER-TRAIN VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Power-train Control (PCM) - Standard Procedure).

No
Perform the POWER-TRAIN VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Power-train Control (PCM) - Standard Procedure).
Test complete.

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I looked under possible causes in my manual and this is what I found.

2012 Jeep Truck Patriot 4WD L4-2.4L
Vehicle
Vehicle Probable Cause P0121
P0121
DTC
P0121
Symptom Descriptor
Throttle Position Sensor 1 Performance
Probable Causes
(K922) Throttle Position Sensor (TPS) Ground Circuit Open or High Resistance
5-Volt Supply Circuit Open or High Resistance
5-Volt Supply Circuit Shorted to Ground
5-Volt Supply Circuit Shorted to Voltage
5-Volt Supply Circuit Shorted to the Throttle Position Sensor (TPS) Sensor Ground Circuit
5-Volt Supply Circuit Shorted to the Throttle Position Sensor (TPS) Signal 1 Circuit
Power-train Control Module (PCM)
Throttle Body
Throttle Position Sensor (TPS) Signal 1 Circuit Open or High Resistance
Throttle Position Sensor (TPS) Signal 1 Circuit Shorted to Ground
Throttle Position Sensor (TPS) Signal 1 Circuit Shorted to Voltage
Throttle Position Sensor (TPS) Signal 1 Circuit Shorted to the TPS Sensor Ground Circuit

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Let me know.

Joe