Circuit Description
The Throttle Position (TP) sensor provides a voltage signal which changes relative to the throttle blade angle. The signal voltage varies from about 0.5 volt at idle to about 4.0 volts at Wide Open Throttle (WOT).
The VCM uses the TP signal, one of the most important inputs, for fuel control and for most of the VCM control outputs.
Each time the voltage drops below 1.25 volts and stops, the VCM assumes this value as the 0 throttle angle, and the VCM measures the percent throttle from this point on. The DTC P0123 is a type A DTC. The DTC P1122 is a type D DTC.
Conditions for Setting the DTC
The DTC will set under the following conditions:
| • | The engine is running |
| • | The Throttle Position (TP) sensor signal is greater than 4.9 volts |
Action Taken When the DTC Sets
Important: The scan tool will not indicate default values.
When the P0123 is reported and 1 failure has occurred, the VCM sets the DTC P0123, and the VCM turns ON the MIL.
Conditions for Clearing the MIL/DTC
The VCM turns OFF the MIL after 3 consecutive driving trips without a fault condition present. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (the coolant temperature has risen 22°C (40°F) from the start-up coolant temperature and the engine coolant temperature exceeds 71°C (160°F) during that same ignition cycle) or the scan tool clearing feature has been used.
Diagnostic Aids
The VCM pins GR 12 and GR 27 are spliced together inside the VCM. When checking one of these circuits for a problem, also check the other circuit and the components on the circuit.
The scan tool reads the throttle position in volts. The scan tool 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 will read the throttle angle. 0% = closed throttle. 100% = WOT.
Scan the TP sensor while depressing the accelerator pedal with the engine turned off and the ignition turned on. The display should vary from below the 1.25 volts (1250 mV) when the throttle was closed to over 4.5 volts (4500 mV) when the throttle is held at WOT position.
A DTC P0123 will result if the TP ground circuit is open or the TP signal circuit is shorted to the voltage.
A DTC P0122 will result if an open or a short to ground in the 5 volt reference circuit or the TP sensor signal circuit.
Refer to Intermittent Conditions .
Test Description
The numbers below refer to step numbers on the diagnostic table.
-
If the TP signal is greater than 4.8 volts, then the fault is present.
-
With the TP sensor disconnected, the TP signal voltage should go low if the VCM and wiring are OK.
-
The VCM pins GR12 and GR27 are spliced together inside the VCM. This step isolates the two pins from one anther.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 |
Important: Before clearing the DTCs, use the scan tool in order to record the Freeze Frame and the Failure Records data. Using the Clear Info function will lose this data. Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
Does the scan tool display a TP sensor voltage greater than the specified value? | 4.8 V | |||
Does the scan tool display a TP sensor voltage less than the specified value? | 0.2 V | |||
4 | The DTC is intermittent. If no addition DTCs are stored, refer to Diagnostic Aids. Are any addition DTCs stored? | -- | Go to Applicable DTC Table | -- |
5 | With a DVM connected to ground, probe the 5 volt reference circuit (at the TP sensor harness connector). Is the voltage greater than the specified value? | 5.2 V | ||
6 | Probe the TP sensor ground circuit (at the TP sensor connector) with a test light to B+. Is the test light ON? | -- | ||
7 | Replace the TP sensor. Is the action complete? | -- | -- | |
8 | Check for a short to voltage on the TP sensor signal circuit. Was a problem found? | -- | ||
9 |
Is the voltage greater than the specified value? | 5.2 V | ||
With a DVM connected to ground, measure the voltage on the VCM connector terminal GR27. Is the voltage greater than the specified value? | 5.2 V | |||
11 |
Is the voltage greater than the specified value? | 5.2 V | ||
12 | Repair the short to voltage on the 5 volt reference circuit. Refer to Wiring Repairs in Engine Electrical. Is the action complete? | -- | -- | |
13 | Check the sensor ground circuit for an open. Was a problem found? | -- | ||
14 | Repair as necessary. Is the action complete? | -- | -- | |
15 | Replace the EGR valve. Refer to EGR Valve Replacement . Is the action complete? | -- | -- | |
16 | Repair short to voltage on the 5 volt reference circuit (terminal GR27). Refer to Wiring Repairs in Engine Electrical. Is the action complete? | -- | -- | |
17 | Replace the VCM. Important: If the VCM is faulty, program the new VCM. Refer to VCM Replacement/Programming . Is the action complete? | -- | -- | |
18 |
Does the scan tool indicate that this diagnostic Ran and Passed? | -- | ||
19 | Using the scan tool, select Capture Info, Review Info. Are any addition DTCs displayed that have not been diagnosed? | -- | Go to Applicable DTC Table | System OK |
