P0121

[Z71_Tahoe]

So I just had my check engine light code read at the local parts store and it came up as P0121. The guys says it's my throttle pedal position sensor. I googled it and it says throttle body needs cleaned. Anyone know which is the correct diagnosis? I appreciate any and all help.

[swathdiver]

This is what it means on our trucks if this is the ONLY code thrown at the time.

 

P0121
The predicted air flow and the predicted MAP combined are outside a calibrated range for more than 3 seconds.

 

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
 Throttle body for dirt, debris, and coking-Refer to Throttle Body Cleaning .
2. Allow the engine to reach operating temperature. Observe the 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.
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.
4. Take a snapshot of the engine data list while performing the actions listed below. The mass air flow
(MAF) sensor g/s 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 g/s should change smoothly and gradually as the engine speed is increased and is returned to
idle.
 If the MAF sensor g/s does not change smoothly and gradually as the engine speed is increased and
is returned to idle, refer to DTC P0101 or 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.

 

What it is saying is that the sensor has detected air flow ratings out of spec between the MAS and MAP sensors for more than 3 seconds.  I would reset the code and see if it comes back first.  If know mechanical issues show and the MAS and MAP are performing withing specs, then replace the #1 TPS sensor.  There are other considerations if other codes are thrown though.