Circuit Description
The throttle body assembly contains 2 throttle position (TP) sensors. The TP sensors are mounted to the throttle body assembly and are not serviceable. The TP sensors provide a signal voltage that changes relative to throttle blade angle. The engine control module (ECM) supplies the TP sensors with a common 5-volt reference circuit , a common low reference circuit, and 2 independent signal circuits.
The TP sensors have opposite functionality. The TP sensor 1 signal voltage increases from below 1 volt at idle to above 4 volts at wide open throttle (WOT). The TP sensor 2 signal voltage decreases from above 4 volts at idle to below 1 volt at WOT.
If the ECM detects TP sensor 1 signal voltage is too high, this DTC sets.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0123 Throttle Position (TP) Sensor 1 Circuit High Voltage
Conditions for Running the DTC
| • | The ignition is ON, with the engine OFF or the engine is operating. |
| • | The ignition 1 voltage is more than 7 volts. |
| • | DTC P0123 runs continuously once the above conditions are met. |
Conditions for Setting the DTC
The ECM detects the TP sensor 1 signal voltage is more than 4.6 volts for more than 4 seconds.
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 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. |
Diagnostic Aids
The following table illustrates the ECM connector locations:
ECM Connector Location | |
|---|---|
C2 | C1 |
Front of Vehicle | |
| • | Use the J 35616-A/BT-8637 GM Approved Terminal Test Kit for any test that requires probing the ECM harness connector or a component harness connector. |
| • | If there is a condition with the TP sensors the ECM defaults to reduced power mode for the entire ignition cycle, even if the condition is corrected. |
| • | For an intermittent condition, refer to Intermittent Conditions . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step verifies that a condition exists.
-
This step tests the signal circuit for a short to voltage. If the scan tool displays a voltage after the TP sensor is disconnected, the circuit is shorted to a voltage.
-
This step tests for high resistance in the low reference circuit of the TP sensor. The ECM must be completely powered down to obtain an accurate resistance reading. It may take up to 30 minutes for the ECM to power down after the ignition key is removed. Removal of the ECM fuse, or the PCM/ETC fuse, allows the ECM to power down completely.
-
This step tests the low reference circuit for a short to voltage.
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 - Vehicle? | -- | Go to Step 2 | |
Is the voltage more than the specified value? | 4.5 V | Go to Step 5 | Go to Step 3 | |
3 | Observe the DTC information with a scan tool. Did DTC P0223 fail this ignition? | -- | Go to Step 5 | Go to Step 4 |
4 |
Did the DTC fail this ignition? | -- | Go to Step 5 | Go to Diagnostic Aids |
Notice: Refer to Disengaging Connectors Notice in the Preface section. Is the voltage less than the specified value? | 0.1 V | Go to Step 6 | Go to Step 9 | |
6 | Measure the voltage between the 5-volt reference circuit of the throttle position (TP) sensor and the engine control module (ECM) housing with a DMM. Is the voltage more than the specified value? | 5.2 V | Go to Step 10 | Go to Step 7 |
Notice: Do NOT use a test lamp to test the continuity of the circuit. Damage to the control module may occur due to excessive current draw. Is the resistance less than the specified value? | 5 ohms | Go to Step 12 | Go to Step 8 | |
Is the voltage less than the specified value? | 1 V | Go to Step 11 | Go to Step 14 | |
9 | Test the signal circuit of the TP sensor 1 for a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 13 |
10 |
Important: The engine control module (ECM) for this engine is not equipped with 5-volt reference DTCs. 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 and all shared 5-volt reference circuits for a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 13 |
11 |
Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 13 |
12 | Test for shorted terminals and for poor connections at the TP sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 15 |
13 | Test for shorted terminals and for poor connections at the ECM. Refer to Circuit Testing and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 16 |
14 |
Important: The control module and/or the TP sensor may be damaged if the circuit is shorted to battery positive voltage. Repair the short voltage in the low reference circuit of TP sensor. Refer to Wiring Repairs . Did you complete the repair? | -- | Go to Step 17 | -- |
15 | Replace the throttle body assembly. Refer to Throttle Body Assembly Replacement . Did you complete the replacement? | -- | Go to Step 17 | -- |
16 | Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 17 | -- |
17 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 18 |
18 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |
