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Gm Tech (Cam)
Gm Tech (Cam), GMC Mechanic
Category: GMC
Satisfied Customers: 29427
Experience:  GM Grand Master Technician 2007. 14 year experience.
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When scanned my vehicle pulls po121 TPS code. I replaced the

Customer Question

When scanned my vehicle pulls po121 TPS code. I replaced the TPS and the code has returned even though the vehicle is running much smoother. I need to rid myself of this code so I can be inspected.
Submitted: 1 year ago.
Category: GMC
Expert:  Gm Tech (Cam) replied 1 year ago.

Hi there, You replaced the throttle body or the pedal in the cabin?

Customer: replied 1 year ago.
I replaced the electronic piece on the side of the throttle body valve
Expert:  Gm Tech (Cam) replied 1 year ago.

Ok, did you check any wiring, pins in the connector back to the Powertrain Control Module (PCM)?

Customer: replied 1 year ago.
The pins on the old TPS were broken but the clip pins looked good.
Expert:  Gm Tech (Cam) replied 1 year ago.

OK, that is the electrical connector that goes into the side?

Customer: replied 1 year ago.
Expert:  Gm Tech (Cam) replied 1 year ago.

But you replaced the plate and not that connector. I am thinking with the new sensor that the connector is the next place to go. That code suggests that the throttle sensors are not matching.

Customer: replied 1 year ago.
How do I test that?
Expert:  Gm Tech (Cam) replied 1 year ago.

The connector you simply cut and replace one wire at a time with a new connector end. The sensor you installed, did you have any issues installing it?

Customer: replied 1 year ago.
I had to index the butterfly valve a little open to get it to seat properly.
Customer: replied 1 year ago.
But where the truck was hesitating leaving idle and bogging down some, all of that is gone.
Expert:  Gm Tech (Cam) replied 1 year ago.

Ok, and clearing the codes does not keep them gone?

Customer: replied 1 year ago.
No sir, it came back fairly quickly both times
Expert:  Gm Tech (Cam) replied 1 year ago.

OK. One moment.

Expert:  Gm Tech (Cam) replied 1 year ago.

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.

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.

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.

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.

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.

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