DTC P0122 Throttle Position (TP) Sensor Circuit Low Voltage. Chevrolet Chevy P42 Commercial Chassis 1999

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 1999 🢒 Chevy P42 Commercial Chassis 🢒 Engine 🢒 Engine Controls - 5.0L and 5.7L 🢒 DTC P0122 Throttle Position (TP) Sensor Circuit Low Voltage

TP/IAC/PCV - Comp Loc Figure
Cell 21: Engine Data Sensors - MAP, IAT, TP ECT
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The throttle position (TP) sensor is a potentiometer. The control module supplies the TP sensor a reference voltage, a signal, and ground circuits. When the throttle is depressed, the TP sensor signal rises to near the reference voltage. When the throttle is released, the TP sensor signal decreases from the reference voltage. The control module monitors the TP sensor signal circuit voltage in order to determine the throttle blade angle, or opening.

This DTC is designed to detect a TP sensor signal voltage lower than the possible operating range of a normally functioning TP sensor.

Conditions for Running the DTC

The engine is running

Conditions for Setting the DTC

The TP sensor signal voltage is less than 0.25 volts for 1 second or more.

Action Taken When the DTC Sets

•	The control module illuminates the malfunction indicator lamp (MIL) if a failure is detected during 2 consecutive key cycles.

•	The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in the scan tool Freeze Frame/Failure Records.

Conditions for Clearing the MIL or DTC

•	The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed.

•

A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle.

•	Use a scan tool in order to clear the DTCs.

Diagnostic Aids

The scan tool displays the throttle position in volts. It should display 0.45-0.85 volts with the throttle closed and the ignition ON or at idle. The voltage should increase at a steady rate as the throttle is moved toward the Wide Open Throttle (WOT) position. Also, the scan tool displays the throttle angle percentage: 0 percent equals closed throttle; 100 percent equals Wide Open Throttle (WOT).

An open or short to ground in the 5 volt reference circuit or the TP sensor signal circuit results in a DTC P0122.

Refer to Symptoms

Scan the TP sensor signal while depressing the accelerator pedal with the engine stopped and the ignition ON. The display should vary from less than 1.25 volts (1250 mV) with the throttle closed, to more than 4.5 volts (4500 mV) when the throttle is held at the Wide Open Throttle (WOT) position.

An intermittent may be caused by any of the following conditions:

•	A poor connection

•	Rubbed through wire insulation

•	A broken wire inside the insulation

Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

If the TP signal measures less than 0.25 volt, then the low voltage condition exists.

If the VCM recognizes the high signal voltage, the VCM and the wiring are okay.

The 5 volt reference of the VCM supply is shared by the MAP, FTP, TP, and EGR position sensors. A short to ground at ANY of the sensors 5 volt reference circuits OR an internally shorted sensor may cause this DTC to set. In order to determine the location of a shorted 5 volt reference supply, disconnect the sensors one at a time beginning with the MAP sensor.

The sensor connectors must remain disconnected while the VCM C3 connector remains connected for this step. The VCM terminals C3 12 and C3 27 are spliced together inside the VCM. When checking the 5 volt reference circuit for a short to ground, both the 5 volt reference circuits must be checked.

Step

Action

Value(s)

Yes

Important: Before clearing the DTCs, use the scan tool Capture Info to save the Freeze Frame and Failure Records for reference. The control module's data is deleted once the Clear Info function is used.

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Install the scan tool.
Turn ON the ignition leaving the engine OFF.
Close the throttle.
Monitor the TP sensor voltage display.

Does the scan tool display a TP sensor voltage less than the specified value?

0.25 V

Go to Step 5

Go to Step 3

Depress the accelerator pedal to WOT (wide open throttle) while monitoring the TP angle on the scan tool.

Does the TP angle increase smoothly through the specified range?

0-100%

Go to Step 4

Go to DTC P0121 Throttle Position (TP) Sensor Performance

The DTC is intermittent.

Are any additional DTCs set?

Go to the applicable DTC table

Go to Diagnostic Aids

Disconnect the TP sensor harness connector.
Turn ON the ignition leaving the engine OFF.
Jumper the TP sensor 5 volt reference circuit and the TP sensor signal circuit together at the TP sensor harness connector.

Does the scan tool display a TP sensor voltage more than the specified value?

4.0 V

Go to Step 13

Go to Step 6

Remove the jumper.
Turn ON the ignition leaving the engine OFF.
Probe the TP sensor 5 volt reference circuit at the TP sensor harness connector with a DMM connected to a ground.

Is the voltage more than the specified value?

4.7 V

Go to Step 14

Go to Step 7

Turn OFF the ignition.
Disconnect the VCM C3 connector.
Check the 5 volt reference circuit for an open.

Did you find a problem?

Go to Step 19

Go to Step 8

Connect the VCM C3 connector.
Turn ON the ignition leaving the engine OFF.
Probe the TP sensor 5 volt reference circuit at the TP sensor harness connector with a J 39200 DMM connected to a ground.
Disconnect the following sensors individually:

•

EGR

•

MAP

•

FTP

Monitor the DMM while disconnecting the sensors.

Did the voltage read more than the specified value after disconnecting one of the sensors?

4.7 V

Go to Step 9

Go to Step 12

Was the suspect sensor the EGR sensor?

Go to Step 10

Go to Step 11

Check for a short between the 5 volt reference circuit and the EGR feed control circuit.

Did you find a problem?

Go to Step 19

Go to Step 11

Replace the sensor that caused the voltage reading to go more than the specified value.
Refer to one of the following: Manifold Absolute Pressure Sensor Replacement , Exhaust Gas Recirculation Valve Replacement , or Fuel Tank Pressure Sensor Replacement .

Is the action complete?

4.7 V

Go to Step 21

Ensure that all sensor connectors are still disconnected.
Turn OFF the ignition.
Probe the 5 volt reference circuit at the TP sensor harness connector with a test lamp connected to B+.

Is the test lamp ON?

Go to Step 16

Go to Step 17

Check for a poor connection at the TP sensor.

Did you find a problem?

Go to Step 19

Go to Step 18

Check the TP sensor signal circuit for a short to ground.

Did you find a problem?

Go to Step 19

Go to Step 15

Check the TP sensor signal circuit for an open.

Did you find a problem?

Go to Step 19

Go to Step 20

Repair the short to ground in the 5 volt reference circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 21

Disconnect the VCM C3 connector.
Check for a poor connection.

Did you find a problem?

Go to Step 19

Go to Step 20

Replace the TP sensor. Refer to Throttle Position Sensor Replacement .

Is the action complete?

Go to Step 21

Repair the circuit as necessary. Refer to Wiring Repairs or Connector Repairs in Wiring Systems.

Is the action complete?

Go to Step 21

Replace the VCM.
Program the new VCM. Refer to VCM Replacement/Programming .
Perform the CKP System Variation Learn Procedure. Refer to Crankshaft Position System Variation Learn .

Is the action complete?

Go to Step 21

Using the scan tool, clear the DTCs.
Start the engine.
Allow the engine to idle until the engine reaches normal operating temperature.
Select DTC and the Specific DTC function.
Enter the DTC number that was set.
Operate the vehicle, within the Conditions for Setting this DTC, until the scan tool indicates the diagnostic Ran.

Does the scan tool indicate the diagnostic Passed?

Go to Step 22

Go to Step 2

Does the scan tool display any additional undiagnosed DTCs?

Go to the applicable DTC table

System OK