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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1567 (Engine Controls Diagnostic (DTC P0068 To DTC P0174) -- 5.7L) >> Diagnosis >> DTC P0120 >> Test Description

Test Description

WARNING: This page is about a different car, the 2004 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.

The number below refers to the step number on the diagnostic table.

  1. 33:  When the TAC module detects a condition within the TAC System, more than one TAC System related DTC may set. This is due to the many redundant tests that run continuously on this system. Locating and repairing 1 individual condition may correct more than 1 DTC. Disconnecting the components during testing may set additional DTCs. Keep this in mind when reviewing the Capture Info.
DTC P0120

Step Action Values Yes No
Schematic References: Engine Controls Schematics
Connector End View References:  Powertrain Control Module (PCM) Connector End Views  , or  Engine Controls Connector End Views 
1 Did you perform the Diagnostic System Check-Engine Controls? - Go to Step 2  Go to Diagnostic System Check - Engine Controls
2 Is DTC P1515, P1516, or P1518 also set? - Go to Diagnostic Trouble Code (DTC) List Go to Step 3 
3
  1. Turn OFF the ignition.
  2. Remove the air inlet duct from the throttle body assembly.
  3. Disconnect the throttle actuator motor harness connector.
  4. Turn ON the ignition, with the engine OFF.
  5. Manually close the throttle blade completely while observing the throttle position (TP) sensor 1 voltage on the scan tool.
Does the scan tool indicate TP sensor 1 voltage within the specified values?		 0.13-0.67 V Go to Step 4  Go to Step 8 
4 Manually open the throttle blade to wide open throttle (WOT) while observing the TP sensor 1 voltage parameter on the scan tool.
Does the scan tool indicate that the TP sensor 1 voltage is within the specified values?		 4.09-4.87 V Go to Step 5  Go to Step 8 
5
  1. Disconnect the TP sensor harness connector.
  2. Disconnect the throttle actuator control (TAC) module harness connector containing the TP sensor circuits.
  3. With a DMM, test the TP sensor low reference circuit 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 32  Go to Step 6 
6
  1. Turn OFF the ignition for 15 seconds.
  2. Reconnect the TAC module harness connector.
  3. Reconnect the throttle actuator motor harness connector.
  4. Reinstall the air inlet duct.
  5. Turn ON the ignition, with the engine OFF.
  6. Select the DTC Info on the scan tool.
  7. Lightly touch and move the related engine wiring harnesses and connectors for the TP sensor while observing the DTC Info. The DTC will set if an intermittent condition is present. Refer to Connector Repairs and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 32  Go to Step 7 
7
  1. Continue to observe DTC Info.
  2. Slowly depress the accelerator pedal to WOT, and then slowly return the pedal to the released position 3 times.
Does the scan tool indicate this DTC failed this ignition?		 - Go to Step 27  Go to Diagnostic Aids
8
  1. Disconnect the TP sensor harness connector.
  2. Measure voltage at the TP sensor 1 signal circuit with a DMM connected to ground.
Does the DMM indicate voltage within the specified values?		 3.94-6.06 V Go to Step 13  Go to Step 9 
9
  1. Turn OFF the ignition.
  2. Disconnect the TAC module harness connector containing the TP sensor circuits.
  3. Turn ON the ignition with the engine OFF.
  4. With a DMM, test the TP sensor 1 signal circuit 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 32  Go to Step 10 
10 With a DMM, test the TP sensor 1 signal circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 32  Go to Step 11 
11 With a DMM, test the TP sensor 1 signal circuit 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 32  Go to Step 12 
12
  1. Disconnect the other TAC module harness connector.
  2. With a DMM, test for a short between the TP sensor 1 signal circuit and all other TAC module circuits. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 32  Go to Step 28 
13 With a DMM, test the TP sensor 1, 5-volt reference circuit for voltage.
Does the DMM indicate voltage within the specified values?		 3.94-6.06 V Go to Step 23  Go to Step 14 
14 Does the DMM indicate voltage greater than the specified value? 6.06 V Go to Step 15  Go to Step 17 
15
  1. Turn OFF the ignition.
  2. Disconnect the TAC module harness connector containing the TP sensor circuits.
  3. Turn ON the ignition with the engine OFF.
  4. With a DMM, test the TP sensor 1 5-volt reference circuit 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 32  Go to Step 16 
16
  1. Turn OFF the ignition.
  2. Disconnect the accelerator pedal position (APP) sensor harness connector.
  3. Disconnect the other TAC module harness connector.
  4. Turn ON the ignition, with the engine OFF.
  5. With a DMM, test the APP sensor 1 5-volt reference circuit 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 32  Go to Step 21 
17 Disconnect the APP sensor.
Does the DMM indicate voltage less than the specified value?		 3.94 V Go to Step 18  Go to Step 30 
18
  1. Disconnect the TAC module harness connector containing the TP sensor circuits.
  2. With a DMM, test the TP sensor 1 5-volt reference circuit for an open or for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 32  Go to Step 19 
19 With a DMM, test the TP sensor 1 5-volt reference circuit for a short to ground.
Did you find and correct the condition?		 - Go to Step 32  Go to Step 20 
20 With a DMM, test the APP sensor 1 5-volt reference circuit 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 32  Go to Step 21 
21 With a DMM, test for a short between the TP sensor 1 5-volt reference circuit and all other TAC module circuits. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 32  Go to Step 22 
22 With a DMM, test for a short between the APP sensor 1 5-volt reference circuit and all other TAC module circuits. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 32  Go to Step 28 
23
  1. Disconnect the TAC module connector containing the TP sensor circuits.
  2. With a DMM, test the TP sensor 1 signal circuit for a short to any other TP sensor circuit. If a short is found refer to Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 32  Go to Step 24 
24
  1. Reconnect the TAC module harness connector containing the TP sensor circuits.
  2. Connect a fused jumper between the TP sensor 1 low reference circuit and the TP sensor 1 signal circuit.
  3. With a scan tool, observe the TP sensor 1 voltage parameter.
Does the scan tool indicate voltage near the specified value?		 0 V Go to Step 26  Go to Step 25 
25
  1. Turn OFF the ignition.
  2. Disconnect the TAC Module harness connector containing the TP sensor circuits.
  3. With a DMM, test the TP sensor 1 low reference circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 32  Go to Step 28 
26 Inspect for poor connections at the TP sensor harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 32  Go to Step 29 
27 Inspect for poor connections at the APP module harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 32  Go to Step 30 
28 Inspect for a poor connection at the TAC Module harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 32  Go to Step 31 
29
IMPORTANT: The throttle position sensor is not a serviceable part and should only be replaced with the throttle body assembly.
Replace the throttle body assembly. Refer to Throttle Body Assembly Replacement .Did you complete the replacement?		 - Go to Step 32  -
30 Replace the APP sensor. Refer to Accelerator Pedal Position (APP) Sensor Replacement .
Did you complete the replacement?		 - Go to Step 32  -
31 Replace the TAC module. Refer to Throttle Actuator Control (TAC) Module Replacement .
Did you complete the replacement?		 - Go to Step 32  -
32
  1. Use the scan tool to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze/Frame Failure Records.
Does the DTC run and pass?		 - Go to Step 33  Go to Step 2 
33  Observe the Capture Info with a scan tool.
Are there any DTCs that have not been diagnosed?		 - Go to Diagnostic Trouble Code (DTC) List System OK
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