DTC 21 TP Sensor Circuit High L57 MFI
Circuit Description
The throttle position (TP) sensor provides a voltage signal which changes relative to the throttle blade angle. The TP sensor signal voltage varies from about 0.5 volt, at idle, to about 5.0 volts at wide open throttle (WOT).
The TP sensor signal is used by the TCM for most of the TCM control outputs.
Each time the voltage drops below 1.25 volts and stops, the TCM assumes this value as the 0 throttle angle. The TCM measures the percent throttle from this point on.
Conditions for Running the DTC
The engine is running.
Conditions for Setting the DTC
The TP sensor signal is greater than 4.9 volts for greater than 1 second.
Action Taken When the DTC Sets
Important:: The scan tool does not indicate default values.
| • | The TCM does not illuminate the MIL. |
| • | The TCM commands maximum line pressure. |
| • | The TCM uses 35% TP as a default. |
| • | The TCM inhibits 4th gear if in hot mode. |
| • | The TCM stores DTC 21 in TCM history. |
Conditions for Clearing the DTC
| • | A scan tool clears the DTC from TCM history. |
| • | The TCM clears the DTC from TCM history if the vehicle completes 40 consecutive key cycles without a diagnostic fault occurring. |
| • | The TCM cancels the DTC default actions when the fault no longer exists, and the ignition switch is OFF long enough in order to power down the TCM. |
Diagnostic Aids
The scan tool reads the throttle position in volts. The TP should read about 0.45 to 0.85 volt, with the throttle closed and the ignition switch turned ON, or at idle. The voltage should increase at a steady rate as the throttle is moved toward the wide open throttle (WOT).
Also, some scan tools read the throttle angle. 0% = closed throttle. 100% = WOT.
Scan the TP sensor while depressing the accelerator pedal with the engine stopped and the ignition ON. The display should vary from below 1.25 volts (1250 mV) when the throttle was closed, to over 4.5 volts (4500 mV) when the throttle is held at the wide open throttle (WOT) position.
This DTC results if the TP ground circuit is open or the TP signal circuit is shorted to the voltage.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
If the TP signal measures greater than 4.9 volts, then the fault exists.
-
With the TP sensor disconnected, and if the TCM and the wiring are okay, the TP signal should go low.
-
Probing the TP ground circuit with a test lamp checks the 5.0 volt return circuit. This step isolates a faulty sensor, the TCM, or an open TP ground circuit.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
Important: Before clearing the DTCs, use the scan tool in order to record the Failure Records. Using the Clear Info function erases the Failure Records from the TCM. Does the Scan Tool display a TP sensor signal greater than the specified value? | 4.9 volts | |||
Does the Scan Tool display a TP sensor signal less than the specified value? | 0.2 volts | |||
The DTC is intermittent. If no additional DTCs are stored, refer to the Diagnostic Aids. If additional DTCs are stored, refer to those tables first. Are any additional DTCs stored? | -- | Go to the Applicable DTC Table | -- | |
5 | With a J 39200 digital multimeter (DMM) connected to ground, probe the 5 V reference circuit (at the TP sensor electrical connector). Is the voltage greater than the specified value? | 5.2 volts | ||
6 | Probe the TP sensor ground circuit (at the TP sensor connector) with a test light connected to B+. Is the test lamp on? | -- | ||
7 | Replace the TP sensor. Refer to Throttle Position Sensor Replacement in Engine Controls. Is the replacement complete? | -- | -- | |
8 | Inspect for a short to voltage in the TP sensor signal circuit. Was a shorted condition found? | -- | ||
9 |
Is the voltage greater than the specified value? | 5.2 volts | ||
10 | Inspect for a short to voltage on the 5 V reference circuit 416 (GRY). Refer to General Electrical Diagnosis in Wiring Systems. Was a short to B+ voltage found? | -- | Go to Diagnostic Aids | |
11 | Check the sensor ground circuit 452 (BLK) for an open. Refer to General Electrical Diagnosis in Wiring Systems. Was an open condition found? | -- | ||
12 | Repair as necessary. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | -- | |
13 | Repair the short to voltage on the 5 V reference circuit 416 (GRY). Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | -- | |
14 |
Important:: If the TCM is faulty, reuse the PROM (Mem-cal). Replace the TCM. Is the replacement complete? | -- | -- | |
15 | Perform the following procedure in order to verify the repair:
Is the Scan Tool TP sensor voltage within the specified value? | 0.5-1.25 volts DC | System OK |
