Circuit Description
The throttle position (TP) sensors 1 and 2 are located within the throttle body assembly. The TP sensors share a common 5-volt reference circuit and a common low reference circuit. The 5-volt reference circuit is also shared with accelerator pedal position (APP) sensor 2. The 5-volt reference voltage is supplied on 2 separate engine control module (ECM) terminals, but the terminals are connected internally to the same voltage supply. Each TP sensor has an individual signal circuit which provides the ECM with a signal voltage proportional to the throttle plate movement. When the throttle plate is in the closed position, the TP sensor 1 signal voltage is near the low reference and increases as the throttle plate is opened. TP sensor 2 signal voltage at closed throttle is near the 5-volt reference and decreases as the throttle plate is opened. The ECM compares the signal of the TP sensors to the mass air flow (MAF) sensor when the engine is running to determine if the sensor readings are correct. The control module also compares the signal of TP sensor 1 and TP sensor 2 through the entire range. If the ECM detects a difference of more than 6 percent between sensor 1 and sensor 2, and a difference from the predicted range by more than 9 percent, DTC P0121 sets.
Conditions for Running the DTC
| • | The battery voltage is more than 10 volts. |
| • | The TP voltage is more than 0.17 volts and less than 4.6 volts. |
Conditions for Setting the DTC
| • | The TP sensor 1 disagrees more than 6 percent from TP sensor 2. |
| • | The TP sensor 1 disagrees more than 9 percent from the predicted value. |
| • | The above conditions are met for 280 milliseconds. |
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 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. |
Step | Action | Values | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views | ||||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||
2 | Is DTC P0223 also set? | -- | Go to Step 3 | |||||||||
3 | Is DTC P0221 also set? | -- | Go to Step 8 | Go to Step 4 | ||||||||
4 |
Does the TP sensor 1 voltage increase as the pedal is depressed and decrease as the pedal is released? | -- | Go to Intermittent Conditions | Go to Step 5 | ||||||||
5 |
Is the TP sensor 1 voltage near the specified value? | 5 V | Go to Step 6 | Go to Step 12 | ||||||||
6 | Probe the signal circuit of the TP sensor 1 with a test lamp that is connected to a good ground. Does the test lamp illuminate? | -- | Go to Step 13 | Go to Step 7 | ||||||||
7 |
Is the TP sensor 1 voltage at the specified value? | 0 V | Go to Step 17 | Go to Step 14 | ||||||||
8 | Measure the voltage from the 5-volt reference of the TP sensor to a good ground with the DMM. Is the voltage near the specified value? | 5 V | Go to Step 9 | Go to Step 15 | ||||||||
9 | Probe the 5-volt reference circuit of the TP sensor with a test lamp that is connected to a good ground. Does the test lamp illuminate? | -- | Go to Step 10 | Go to Step 15 | ||||||||
10 |
Important: It may be necessary to remove the ECM/TCM fuse to allow the ECM to power down. Is the resistance less than the specified value? | 5ohms | Go to Step 11 | Go to Step 19 | ||||||||
11 |
Does the MAF sensor g/s change smoothly and gradually through the specified range of the test? | 7-40 g/s | Go to Step 20 | Go to DTC P0101 | ||||||||
12 | Test the signal circuit of the TP sensor 1 for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 22 | Go to Step 20 | ||||||||
13 | Test the signal circuit of the TP sensor 1 for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 22 | Go to Step 20 | ||||||||
14 |
Did you find and correct the condition? | -- | Go to Step 22 | Go to Step 20 | ||||||||
15 |
Did you find and correct the condition? | -- | Go to Step 22 | Go to Step 16 | ||||||||
16 | Test the 5-volt reference circuit of the TP sensor for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 22 | Go to Step 20 | ||||||||
17 | 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 22 | Go to Step 18 | ||||||||
18 | Replace the throttle body assembly. Refer to Throttle Body Assembly Replacement . Did you complete the replacement? | -- | Go to Step 22 | -- | ||||||||
19 | Repair the open or high resistance in the low reference circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 22 | -- | ||||||||
20 | 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 22 | Go to Step 21 | ||||||||
21 | Replace the ECM. Refer to Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 22 | -- | ||||||||
22 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 23 | ||||||||
23 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||
