Circuit Description
The PCM supplies a 5V reference signal and a ground to the TP sensor. The TP sensor sends a voltage signal back to the PCM relative to the throttle plate opening. The voltage signal will vary from approximately 0.45V at closed throttle, to over 4.5V at wide open throttle. The PCM can detect if the TP sensor is out of range while cruising by waiting for a Manifold Air Pressure (MAP) change and then checks if the TP sensor has also changed as expected by calculating what the TP signal should be at a given RPM and engine load. During idle conditions, the PCM verifies that the engine is stable and at idle, and ensures that the TP signal is below a given percent.
Conditions for Setting the DTC
DTC(s) P0107, P0108, P0122, 123 not set.
Idle Test
| • | Vehicle speed is less than 1 mph. |
| • | Engine speed is less than 850 RPM (Auto). |
| • | Engine speed is less than 1200 RPM (Man). |
| • | IAC counts are less than 145 counts. |
| • | Manifold Absolute Pressure (MAP) is stable. |
And
TP angle is greater than 7% at idle after attempting to auto-zero.
Cruise Test
| • | TP is stable ± 2%. |
| • | MAP is less than 37 kPa. |
And
TP angle is greater than the following specified percentages at the given RPMs.
| • | TP angle is greater than 60% at 1600 RPM |
| • | TP angle is greater than 77% at 2400 RPM |
| • | TP angle is greater than 89% at 3200 RPM |
| • | TP angle is greater than 99% at 4000 RPM |
Action Taken When the DTC Sets
| • | The Malfunction Indicator Lamp (MIL) illuminates. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The Freeze Frame and Failure Records buffers stores this information. |
| • | A history DTC is stored. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault. |
| • | A history DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | The MIL/DTCs can be cleared by using the scan tool. |
Diagnostic Aids
| • | A TP sensor that is stuck will attempt an auto zero every time that the engine runs. An indication of this happening would be the TP sensor percentage will be 0 percent and the TP sensor voltage will be high. |
| • | Using a DMM in order to check the TP sensor 5 volt reference circuits may not detect small amounts of resistance. Connecting a jumper wire from the TP sensor 5 volt reference circuit to the TP sensor signal circuit is a better test in this situation. |
| • | Certain conditions can produce normal results when probed, but can cause a bad reading when connected. Check for the following conditions on the TP sensor electrical connectors: |
| • | Spread terminals |
| • | Poor electrical terminal connections |
| • | If a DTC P0121 cannot be duplicated, the information included in the Freeze Frame/Failure Records data can be useful. Use the scan tool DTC information data in order to determine the status of the DTC. |
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
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The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
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The TP sensor has an auto zeroing feature. If the voltage reading is between 0.2 to 0.9 volts, the PCM will assume the TP sensor is at a closed throttle position (0%). If the reading is out of the auto zeroing range at closed throttle, look for a binding or damaged linkage.
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Normal TP voltage when the throttle plates are fully closed is near 0.50 volts. A sensor will display a higher voltage when the sensor is stuck or a circuit is faulty.
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A disconnected TP sensor should not display a voltage reading on the scan tool. An amount less than the specified value is normal.
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When the test light is connected to the ground circuit, the light should glow brightly if the ground circuit may be OK but could have a small amount of resistance in the circuit. The voltmeter is used to detect the small amounts of resistance using the voltage drop method. If the test light glows dimly or not at all, then resistance in the circuit is present and using the voltmeter is not necessary.
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In order for DTC P0121 to set with a short voltage in the TP signal circuit, the voltage must be minimal enough to not set a DTC P0123, and more than 0.5 volts.
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Disconnecting the EGR valve and sensors connected to the 5.0 volt reference circuits internally to the PCM determines if the 5.0 volt reference circuit is shorted or if one of the sensors is causing a short on the 5.0 volt reference circuit.
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Replacement PCMs must be reprogrammed and the crankshaft position system variation procedure must be preformed. Refer to the latest Isuzu Technical Communication System (ITCS) information for programming procedures and also refer to the Powertrain Control Module (PCM) .
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If no faults have been found at this point and no additional DTCs were set, refer to Diagnostic Aids for additional checks and information.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | |||
Does the TP angle value increase steadily when the accelerator pedal is depressed to greater than the specified value and decrease steadily when the pedal is released to less than the specified value? | 98% 1% | |||
Does the scan tool display a TP voltage below the specified value when the throttle is fully closed? | 0.80V | |||
4 |
Is the TP angle vs. RPM value greater than the specified value in theConditions For Setting The DTC ? | -- | ||
Disconnect the TP sensor electrical connector. Is the TP sensor voltage less then the specified value? | 0.5V | |||
Does the DVM read a voltage greater than the specified value? | 0.5V | |||
Check the TP signal circuit for a short to voltage and repair as necessary. Was a repair necessary? | -- | |||
8 | Check the TP sensor ground circuit for a poor connection or resistance at the TP sensor connector and repair as necessary. Was a repair necessary? | -- | ||
9 | With a DVM connected to ground, probe the 5.0 volt reference circuit at the TP sensor connector. Does the DVM display a voltage near the specified value? | 5.0V | ||
Does the DVM display a voltage near the specified value? | 5V | |||
11 |
Is the action complete? | 5V | -- | |
12 | Check for a short to voltage in the 5.0 volt reference circuit and repair if necessary. Was a repair necessary? | -- | ||
13 | Replace the TP sensor. Refer to Throttle Position Sensor Replacement . Is the action complete? | -- | -- | |
14 | Check the PCM electrical connectors for a poor connection or resistance and repair as necessary. Was a repair necessary? | -- | ||
Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | ||
16 |
Does the scan tool indicate that this diagnostic ran and passed? | -- | ||
Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | Go to the applicable DTC table | System OK, refer to Diagnostic Aids |
