P0121 error code
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Joined: Jan 2020
Posts: 88
Likes: 9
From: Sacramento
P0121 error code
Using my Blue Driver OBDII scanner I have P0121 and P0442 P0121, throttle / pedal position sensor / switch A circuit / performanceP0442, small evap leak (possibly gas cap) 2005 C6 LS2 4 speed auto I watched a couple YouTube videos and it sounds like these motors do not have a throttle position sensor.I haven't cleaned the throttle body yet since I need to pick up some spray cleaner. I have cleaned the MAF with MAF cleaner, no changes. My symptom is while stopped, at idle speed, I let off the brake and hit the gas and the car bogs real hard, like too much air, and then goes. Only a few times it has stalled the motor. Also low RPM driving with very little throttle then letting off the gas the RPMs drop to a couple hundred and will bounce up to idle speed or often stall the motor.While in park or neutral I can press the throttle a little and the idle struggles. Press a little more and the RPM goes up but I know the RPMs should be higher due to the throttle pedal position. When driving at 1500 RPM and higher there seems to be no problems. The car is responsive and does what it should.
The car starts and idles fine seems like the issue is low RPMs just above idle.What do you guys think?Could it be the sensor on the gas pedal?Replace the throttle body if it continues after cleaning?Thanks
The car starts and idles fine seems like the issue is low RPMs just above idle.What do you guys think?Could it be the sensor on the gas pedal?Replace the throttle body if it continues after cleaning?Thanks
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Joined: Sep 2013
Posts: 15,595
Likes: 4,055
From: Cape Coral, Florida
Below is the flow chart for the P0121...unfortunately we can't diagnose this for you over the Internet...a smoke machine is the preferred tooling for an EVAP leak...the MAP sensor ignition ON if at sea level should be 101 kPa, 29.9 inches Mercury or 14.7 psi...MAF at idle NO LOAD and at operating temp should be no less than 6.2 grams/second....and YES you have a TPS sensor...a simple 3 wire potentiometer....what are your fuel trims at idle ??...a Blue Driver not the best scan tool for a diagnosis...I keep one in my glovebox for my 08 in case I need to read Powertrain DTC's.
DTC P0068 or P0121
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. See: Vehicle > Initial Inspection and Diagnostic Overview
* Strategy Based Diagnosis
* Diagnostic Procedure Instructions
DTC Descriptors
DTC P0068
- Throttle Body Airflow Performance
DTC P0121
- Throttle Position (TP) Sensor 1 Performance
Circuit/System Description
The engine control module (ECM) uses the following information to calculate an expected airflow rate:
* The throttle position (TP)
* The barometric pressure (BARO)
* The manifold absolute pressure (MAP)
* The intake air temperature (IAT)
* The engine RPM
Conditions for Running the DTC
P0068
* DTCs P0641, P0651, P1516, P2101, P2119, P2176 are not set.
* The engine is running.
* DTC P0068 run continuously when the above conditions are met.
P0121
* DTCs P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0128, P0315, P0335, P0336 are not set.
* The engine speed is more than 450 RPM.
* DTC P0121 run continuously when the above conditions are met.
Conditions for Setting the DTC
P0068
The ECM detects that the throttle position and the indicated engine load do not correspond with the expected load and throttle position for less than 1 second.
P0121
The predicted air flow and the predicted MAP combined are outside a calibrated range for more than 3 seconds.
Action Taken When the DTC Sets
P0068
* DTC P0068 is a Type A DTC.
* The control module commands the throttle actuator control (TAC) system to operate in the Reduced Engine Power mode.
* A message center or an indicator displays Reduced Engine Power.
* Under certain conditions the control module commands the engine OFF.
P0121
DTC P0121 is a Type B DTC.
Conditions for Clearing the MIL/DTC
* DTC P0068 is a Type A DTC.
* DTC P0121 is a Type B DTC.
Circuit/System Testing
1. Inspect for the following conditions:
* Vacuum hoses for splits, kinks, and proper connections as shown on Vehicle Emission Control Information label
* Inspect thoroughly for any type of leak or restriction
* Air leaks at throttle body mounting area and intake manifold sealing surfaces
* Inspect throttle body for dirt, debris, and coking.
2. Allow the engine to reach operating temperature. Observe the Manifold Absolute Pressure (MAP) Sensor Voltage parameter with a scan tool. Voltage should be more than 0.8 volt and less than 4 volts.
♦ If more than 4 volts or less than 0.8 volt, refer to DTC P0106. See: A L L Diagnostic Trouble Codes ( DTC ) > P Code Charts > P0106
3. Idle the engine. Observe the MAP Sensor kPa parameter with a scan tool. Increase the engine speed slowly and then back to idle. The MAP sensor kPa should change smoothly and gradually as engine speed is increased and returned to idle.
♦ If the MAP sensor kPa does not change refer to DTC P0106. See: A L L Diagnostic Trouble Codes ( DTC ) > P Code Charts > P0106
4. Take a snapshot of the engine data list while performing the actions listed below. The mass air flow (MAF) sensor kPa should change smoothly and gradually as the engine speed is increased and is returned to idle.
* Idle the engine.
* Increase the engine speed slowly to 3,000 RPM, then back to idle.
* Exit from the snapshot and review the data.
* Observe the Mass Air Flow (MAF) Sensor parameter frame by frame with a scan tool. The MAF sensor kPa should change smoothly and gradually as the engine speed is increased and is returned to idle.
♦ If the MAF sensor kPa does not change smoothly and gradually as the engine speed is increased and is returned to idle refer to DTC P0101 or P1101. See: A L L Diagnostic Trouble Codes ( DTC ) > P Code Charts > P1101
5. Inspect the throttle body for the following conditions:
* Loose or damaged throttle blade
* Broken throttle shaft
* Any throttle body damage
♦ If any of these conditions exist, replace the throttle body assembly.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
* Throttle Body Assembly Replacement
* Refer to Programming and Relearning. See: Vehicle > Programming and Relearning
DTC P0068 or P0121
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. See: Vehicle > Initial Inspection and Diagnostic Overview
* Strategy Based Diagnosis
* Diagnostic Procedure Instructions
DTC Descriptors
DTC P0068
- Throttle Body Airflow Performance
DTC P0121
- Throttle Position (TP) Sensor 1 Performance
Circuit/System Description
The engine control module (ECM) uses the following information to calculate an expected airflow rate:
* The throttle position (TP)
* The barometric pressure (BARO)
* The manifold absolute pressure (MAP)
* The intake air temperature (IAT)
* The engine RPM
Conditions for Running the DTC
P0068
* DTCs P0641, P0651, P1516, P2101, P2119, P2176 are not set.
* The engine is running.
* DTC P0068 run continuously when the above conditions are met.
P0121
* DTCs P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0128, P0315, P0335, P0336 are not set.
* The engine speed is more than 450 RPM.
* DTC P0121 run continuously when the above conditions are met.
Conditions for Setting the DTC
P0068
The ECM detects that the throttle position and the indicated engine load do not correspond with the expected load and throttle position for less than 1 second.
P0121
The predicted air flow and the predicted MAP combined are outside a calibrated range for more than 3 seconds.
Action Taken When the DTC Sets
P0068
* DTC P0068 is a Type A DTC.
* The control module commands the throttle actuator control (TAC) system to operate in the Reduced Engine Power mode.
* A message center or an indicator displays Reduced Engine Power.
* Under certain conditions the control module commands the engine OFF.
P0121
DTC P0121 is a Type B DTC.
Conditions for Clearing the MIL/DTC
* DTC P0068 is a Type A DTC.
* DTC P0121 is a Type B DTC.
Circuit/System Testing
1. Inspect for the following conditions:
* Vacuum hoses for splits, kinks, and proper connections as shown on Vehicle Emission Control Information label
* Inspect thoroughly for any type of leak or restriction
* Air leaks at throttle body mounting area and intake manifold sealing surfaces
* Inspect throttle body for dirt, debris, and coking.
2. Allow the engine to reach operating temperature. Observe the Manifold Absolute Pressure (MAP) Sensor Voltage parameter with a scan tool. Voltage should be more than 0.8 volt and less than 4 volts.
♦ If more than 4 volts or less than 0.8 volt, refer to DTC P0106. See: A L L Diagnostic Trouble Codes ( DTC ) > P Code Charts > P0106
3. Idle the engine. Observe the MAP Sensor kPa parameter with a scan tool. Increase the engine speed slowly and then back to idle. The MAP sensor kPa should change smoothly and gradually as engine speed is increased and returned to idle.
♦ If the MAP sensor kPa does not change refer to DTC P0106. See: A L L Diagnostic Trouble Codes ( DTC ) > P Code Charts > P0106
4. Take a snapshot of the engine data list while performing the actions listed below. The mass air flow (MAF) sensor kPa should change smoothly and gradually as the engine speed is increased and is returned to idle.
* Idle the engine.
* Increase the engine speed slowly to 3,000 RPM, then back to idle.
* Exit from the snapshot and review the data.
* Observe the Mass Air Flow (MAF) Sensor parameter frame by frame with a scan tool. The MAF sensor kPa should change smoothly and gradually as the engine speed is increased and is returned to idle.
♦ If the MAF sensor kPa does not change smoothly and gradually as the engine speed is increased and is returned to idle refer to DTC P0101 or P1101. See: A L L Diagnostic Trouble Codes ( DTC ) > P Code Charts > P1101
5. Inspect the throttle body for the following conditions:
* Loose or damaged throttle blade
* Broken throttle shaft
* Any throttle body damage
♦ If any of these conditions exist, replace the throttle body assembly.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
* Throttle Body Assembly Replacement
* Refer to Programming and Relearning. See: Vehicle > Programming and Relearning
Last edited by C5 Diag; May 3, 2026 at 06:34 PM.
Thread Starter
Advanced
Joined: Jan 2020
Posts: 88
Likes: 9
From: Sacramento
Below is the flow chart for the P0121...unfortunately we can't diagnose this for you over the Internet...a smoke machine is the preferred tooling for an EVAP leak...the MAP sensor ignition ON if at sea level should be 101 kPa, 29.9 inches Mercury or 14.7 psi...MAF at idle NO LOAD and at operating temp should be no less than 6.2 grams/second....and YES you have a TPS sensor...a simple 3 wire potentiometer....what are your fuel trims at idle ??...a Blue Driver not the best scan tool for a diagnosis...I keep one in my glovebox for my 08 in case I need to read Powertrain DTC's.
DTC P0068 or P0121
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. See: Vehicle > Initial Inspection and Diagnostic Overview
* Strategy Based Diagnosis
* Diagnostic Procedure Instructions
DTC Descriptors
DTC P0068
- Throttle Body Airflow Performance
DTC P0121
- Throttle Position (TP) Sensor 1 Performance
Circuit/System Description
The engine control module (ECM) uses the following information to calculate an expected airflow rate:
* The throttle position (TP)
* The barometric pressure (BARO)
* The manifold absolute pressure (MAP)
* The intake air temperature (IAT)
* The engine RPM
Conditions for Running the DTC
P0068
* DTCs P0641, P0651, P1516, P2101, P2119, P2176 are not set.
* The engine is running.
* DTC P0068 run continuously when the above conditions are met.
P0121
* DTCs P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0128, P0315, P0335, P0336 are not set.
* The engine speed is more than 450 RPM.
* DTC P0121 run continuously when the above conditions are met.
Conditions for Setting the DTC
P0068
The ECM detects that the throttle position and the indicated engine load do not correspond with the expected load and throttle position for less than 1 second.
P0121
The predicted air flow and the predicted MAP combined are outside a calibrated range for more than 3 seconds.
Action Taken When the DTC Sets
P0068
* DTC P0068 is a Type A DTC.
* The control module commands the throttle actuator control (TAC) system to operate in the Reduced Engine Power mode.
* A message center or an indicator displays Reduced Engine Power.
* Under certain conditions the control module commands the engine OFF.
P0121
DTC P0121 is a Type B DTC.
Conditions for Clearing the MIL/DTC
* DTC P0068 is a Type A DTC.
* DTC P0121 is a Type B DTC.
Circuit/System Testing
1. Inspect for the following conditions:
* Vacuum hoses for splits, kinks, and proper connections as shown on Vehicle Emission Control Information label
* Inspect thoroughly for any type of leak or restriction
* Air leaks at throttle body mounting area and intake manifold sealing surfaces
* Inspect throttle body for dirt, debris, and coking.
2. Allow the engine to reach operating temperature. Observe the Manifold Absolute Pressure (MAP) Sensor Voltage parameter with a scan tool. Voltage should be more than 0.8 volt and less than 4 volts.
♦ If more than 4 volts or less than 0.8 volt, refer to DTC P0106. See: A L L Diagnostic Trouble Codes ( DTC ) > P Code Charts > P0106
3. Idle the engine. Observe the MAP Sensor kPa parameter with a scan tool. Increase the engine speed slowly and then back to idle. The MAP sensor kPa should change smoothly and gradually as engine speed is increased and returned to idle.
♦ If the MAP sensor kPa does not change refer to DTC P0106. See: A L L Diagnostic Trouble Codes ( DTC ) > P Code Charts > P0106
4. Take a snapshot of the engine data list while performing the actions listed below. The mass air flow (MAF) sensor kPa should change smoothly and gradually as the engine speed is increased and is returned to idle.
* Idle the engine.
* Increase the engine speed slowly to 3,000 RPM, then back to idle.
* Exit from the snapshot and review the data.
* Observe the Mass Air Flow (MAF) Sensor parameter frame by frame with a scan tool. The MAF sensor kPa should change smoothly and gradually as the engine speed is increased and is returned to idle.
♦ If the MAF sensor kPa does not change smoothly and gradually as the engine speed is increased and is returned to idle refer to DTC P0101 or P1101. See: A L L Diagnostic Trouble Codes ( DTC ) > P Code Charts > P1101
5. Inspect the throttle body for the following conditions:
* Loose or damaged throttle blade
* Broken throttle shaft
* Any throttle body damage
♦ If any of these conditions exist, replace the throttle body assembly.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
* Throttle Body Assembly Replacement
* Refer to Programming and Relearning. See: Vehicle > Programming and Relearning
DTC P0068 or P0121
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. See: Vehicle > Initial Inspection and Diagnostic Overview
* Strategy Based Diagnosis
* Diagnostic Procedure Instructions
DTC Descriptors
DTC P0068
- Throttle Body Airflow Performance
DTC P0121
- Throttle Position (TP) Sensor 1 Performance
Circuit/System Description
The engine control module (ECM) uses the following information to calculate an expected airflow rate:
* The throttle position (TP)
* The barometric pressure (BARO)
* The manifold absolute pressure (MAP)
* The intake air temperature (IAT)
* The engine RPM
Conditions for Running the DTC
P0068
* DTCs P0641, P0651, P1516, P2101, P2119, P2176 are not set.
* The engine is running.
* DTC P0068 run continuously when the above conditions are met.
P0121
* DTCs P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0128, P0315, P0335, P0336 are not set.
* The engine speed is more than 450 RPM.
* DTC P0121 run continuously when the above conditions are met.
Conditions for Setting the DTC
P0068
The ECM detects that the throttle position and the indicated engine load do not correspond with the expected load and throttle position for less than 1 second.
P0121
The predicted air flow and the predicted MAP combined are outside a calibrated range for more than 3 seconds.
Action Taken When the DTC Sets
P0068
* DTC P0068 is a Type A DTC.
* The control module commands the throttle actuator control (TAC) system to operate in the Reduced Engine Power mode.
* A message center or an indicator displays Reduced Engine Power.
* Under certain conditions the control module commands the engine OFF.
P0121
DTC P0121 is a Type B DTC.
Conditions for Clearing the MIL/DTC
* DTC P0068 is a Type A DTC.
* DTC P0121 is a Type B DTC.
Circuit/System Testing
1. Inspect for the following conditions:
* Vacuum hoses for splits, kinks, and proper connections as shown on Vehicle Emission Control Information label
* Inspect thoroughly for any type of leak or restriction
* Air leaks at throttle body mounting area and intake manifold sealing surfaces
* Inspect throttle body for dirt, debris, and coking.
2. Allow the engine to reach operating temperature. Observe the Manifold Absolute Pressure (MAP) Sensor Voltage parameter with a scan tool. Voltage should be more than 0.8 volt and less than 4 volts.
♦ If more than 4 volts or less than 0.8 volt, refer to DTC P0106. See: A L L Diagnostic Trouble Codes ( DTC ) > P Code Charts > P0106
3. Idle the engine. Observe the MAP Sensor kPa parameter with a scan tool. Increase the engine speed slowly and then back to idle. The MAP sensor kPa should change smoothly and gradually as engine speed is increased and returned to idle.
♦ If the MAP sensor kPa does not change refer to DTC P0106. See: A L L Diagnostic Trouble Codes ( DTC ) > P Code Charts > P0106
4. Take a snapshot of the engine data list while performing the actions listed below. The mass air flow (MAF) sensor kPa should change smoothly and gradually as the engine speed is increased and is returned to idle.
* Idle the engine.
* Increase the engine speed slowly to 3,000 RPM, then back to idle.
* Exit from the snapshot and review the data.
* Observe the Mass Air Flow (MAF) Sensor parameter frame by frame with a scan tool. The MAF sensor kPa should change smoothly and gradually as the engine speed is increased and is returned to idle.
♦ If the MAF sensor kPa does not change smoothly and gradually as the engine speed is increased and is returned to idle refer to DTC P0101 or P1101. See: A L L Diagnostic Trouble Codes ( DTC ) > P Code Charts > P1101
5. Inspect the throttle body for the following conditions:
* Loose or damaged throttle blade
* Broken throttle shaft
* Any throttle body damage
♦ If any of these conditions exist, replace the throttle body assembly.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
* Throttle Body Assembly Replacement
* Refer to Programming and Relearning. See: Vehicle > Programming and Relearning
I purchase throttle body spray cleaner and removed the throttle body. During the examination it was obviously dirty so I cleaned it sparkly clean. I also cleaned the MAF with MAF cleaner too. Reinstalled everything and left it disconnected from the batter over 12 hours.
The hesitation issue is completely gone! I thought I had a vacuum leak somewhere but a dirty throttle body was my issue.
As for the evap error I will wait to see it the check engine light comes back before I attach my smoke machine to find the leak.
Thanks again for your support and help.
crusties on the edge
just plain dirty
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,595
Likes: 4,055
From: Cape Coral, Florida
You didn't have to remove the TB to clean it...a scan tool has a data PID which can tell you if it may be dirty...I clean mine every other year as preventive maintenance along with the MAF...just the area where the throttle blade rides on the bore needs to be cleaned.
Thread Starter
Advanced
Joined: Jan 2020
Posts: 88
Likes: 9
From: Sacramento
