Circuit Description
The throttle position (TP) sensor is used by the engine control module (ECM) to determine the throttle plate angle for various engine management systems. The TP sensor is a potentiometer type sensor with 3 circuits:
| • | A 5-volt reference circuit |
| • | A low reference circuit |
| • | A TP sensor signal circuit |
The ECM provides the TP sensor with 5 volts on the 5-volt reference circuit, and a ground on the low reference circuit. The TP sensor provides a signal voltage that changes relative to throttle plate angle. The TP sensor signal voltage at idle is less than 0.5 volt. The TP sensor voltage is typically near 0.0 volts at idle, but could be as high as 0.5 volts. The TP sensor voltage should increase to above 4 volts at wide open throttle (WOT). If the ECM detects an excessively low signal voltage, DTC P0122 sets.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0122 Throttle Position (TP) Sensor Circuit Low Voltage
Conditions for Running the DTC
| • | The ignition is ON or the engine is running. |
| • | DTC P0122 runs continuously once the above condition is met. |
Conditions for Setting the DTC
Important: The scan tool displays a voltage near 0.0 volts. Do not use the scan tool voltage parameter to determine if there is a TP sensor condition.
The ECM detects that the TP sensor signal voltage is less than 0.14 volt for a total of 2.5 seconds during a 5 second period.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 4 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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If the DTC P0122 cannot be duplicated, the information included in the Freeze Frame data can be useful. Use the scan tool information to determine the status of the DTC. If the DTC occurs intermittently, using intermittent conditions may isolate the condition.
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This step determines if there is a short to ground or an open condition in the circuits.
Step | Action | Values | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views | ||||||||||
1 | Did you perform the Diagnostic System Check - Engine Controls? | -- | Go to Step 2 | |||||||
2 |
Does the TP sensor angle increase from below the first specified value to above the second specified value? | 15% 85% | Go to Step 3 | Go to Step 4 | ||||||
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Intermittent Conditions | |||||||
Is the voltage more than the specified value? | 4.8 V | Go to Step 5 | Go to Step 7 | |||||||
5 |
Is the percentage more than the specified value? | 85% | Go to Step 6 | Go to Step 8 | ||||||
6 | Measure the resistance between the low reference circuit of the TP sensor and the engine control module (ECM) housing with a DMM. Is the resistance less than the specified value? | 2 ohms | Go to Step 10 | Go to Step 9 | ||||||
7 |
Important: The 5-volt reference circuits are internally and externally connected at the controller. Other sensors that share the 5-volt reference circuit may also have DTCs set. Disconnecting a sensor on the shared 5-volt reference circuit may isolate a shorted sensor. Review the electrical schematic and diagnose the shared circuits and sensors. Test the 5-volt reference circuit of the TP sensor for the following conditions:
Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 11 | ||||||
8 | Test the signal circuit of the TP sensor for the following conditions:
Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 11 | ||||||
9 |
Important: The ECM and/or the TP sensor may be damaged if the low reference circuit is shorted to battery positive voltage. Test the low reference circuit of the TP sensor for the following conditions:
Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 11 | ||||||
10 | Test for an intermittent and for a poor connection at the TP sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 12 | ||||||
11 | Test for an intermittent and for a poor connection at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 13 | ||||||
12 | Replace the TP sensor. Refer to Throttle Position Sensor Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- | ||||||
13 | Replace the ECM. Refer to Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- | ||||||
14 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 15 | ||||||
15 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||
