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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1382 (Engine Control System Diagnosis (DTC P0010 To DTC P0128) -- 1.8L (LNK)) >> Diagnosis >> DTC P0121 >> Test Description

Test Description

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

The numbers below refer to the step numbers on the diagnostic table.

  1. 1:  The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the Freeze Frame 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.
  2. 2:  The throttle angle percentage should steadily increase without binding or a large percentage jump.
  3. 3:  This step determines if DTC P0121 is the result of a hard failure or an intermittent condition.
  4. 4:  This step inspects for an open or a short in the FTP sensor 5-volt reference.
  5. 5:  This step inspects for excessive resistance in the reference voltage circuit. If the test lamp does not illuminate at all, there is resistance in the circuit.
  6. 7:  When the 5-volt reference circuit is jumpered to the TP sensor input circuit, the scan tool parameter should read near 100 percent.
DTC P0121

Step Action Values Yes No
Schematic Reference:  Engine Controls Schematics 
1  Did you perform the Diagnostic System Check-Engine Controls? - Go to Step 2  Go to Diagnostic System Check - Engine Controls
2 
  1. Turn ON the ignition, with the engine OFF.
  2. Install a scan tool.
  3. Select the TP angle parameter on the scan tool.
  4. Monitor the scan tool while depressing the accelerator pedal, repeat the procedure several times.
Does the TP angle value increase steadily when the accelerator pedal is depressed and decrease steadily when the pedal is released, within the specified range?		 8-80% Go to Step 3  Go to Step 4 
3 
  1. Perform the scan tool Clear DTC Information function.
  2. Place the vehicle into Check Mode operation using the scan tool. Refer to Service Bay Test .
  3. Operate the vehicle within the Freeze Frame conditions as specified.
Does DTC P0121 set?		 - Go to Step 4  Go to Diagnostic Aids
4 
  1. Connect DMM between the TP sensor reference voltage circuit on the harness side and ground.
  2. Turn ON the ignition, leaving the engine OFF.
Is the TP sensor voltage at the specified value?		 5 V Go to Step 5  Go to Step 6 
5 
  1. Connect a test lamp between the reference voltage circuit and ground.
  2. Turn ON the ignition, leaving the engine OFF.
Does the test lamp illuminate at least dimly?		 - Go to Step 7  Go to Step 9 
6
  1. Inspect for the following conditions:
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.
Did you complete the repair?		 - Go to Step 12  -
7 
  1. Connect a test lamp between the TP sensor input circuit and the TP sensor reference voltage circuit at the harness connector.
  2. Monitor the TP angle on the scan tool.
Is the TP sensor percentage more than the specified value?		 90% Go to Step 10  Go to Step 8 
8
  1. Check for the following conditions:
    • High resistance in the TP sensor ground circuit between the sensor and S206
    • High resistance in the TP sensor input circuit between the TP sensor and the PCM
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.
Was a repair necessary?		 - Go to Step 12  Go to Step 11 
9 Locate and repair the high resistance in the reference voltage circuit of the TP sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems.
Did you complete the repair?		 - Go to Step 12  -
10 Replace the TP sensor. Refer to Throttle Position (TP) Sensor Replacement .
Is the action complete?		 - Go to Step 12  -
11 Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement .
Is the action complete?		 - Go to Step 12  -
12
  1. Use the scan tool in order 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 as specified in the supporting text.
Does the DTC run and pass?		 - Go to Step 13  Go to Step 2 
13 With a scan tool, observe the stored information, Capture Info.
Does the scan tool display any DTCs that you have not diagnosed?		 - Go to Diagnostic Trouble Code (DTC) List System OK
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