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Home >> Cadillac >> 2005 >> DeVille Protection Series >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls (DTC P0016 To P0137) >> Diagnostic Information & Procedures >> DTC P0121 >> Test Description

Test Description

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

  1. 8:  This step calculates the resistance in the 5-volt reference circuit.
  2. 9:  This step calculates the resistance in the low reference circuit.
DTC P0121

Step Action Values Yes No
Schematic Reference: Engine Controls Schematics
Connector End View Reference: Engine Controls Connector End Views or Powertrain Control Module (PCM) Connector End Views
1 Did you perform the Diagnostic System Check - Vehicle? - Go to Step 2  Go to Diagnostic System Check - Vehicle in Vehicle DTC Information
2
  1. Turn ON the ignition, with the engine OFF.
  2. Observe the DTC information with a scan tool.
Is DTC P0641 also set?		 - Go to DTC P0641 Go to Step 3 
3
  1. Turn OFF the ignition.
  2. Turn ON the ignition, with the engine OFF.
  3. Observe the TP sensor parameter with a scan tool.
Is the voltage less than the specified value with the throttle in the closed position?		 0.85 V Go to Step 4  Go to Step 6 
4
  1. Observe the TP sensor parameter with the scan tool.
  2. Press the accelerator pedal slowly until the throttle is in the wide open position.
  3. Release the accelerator pedal slowly until the throttle is returned to the closed position.
  4. Repeat this procedure several times.
Does the TP sensor parameter increase steadily when the pedal is depressed, to more than the first specified value, and then decrease steadily when the pedal is released, returning to less than the second specified value?		 98%
1%		 Go to Step 5  Go to Step 7 
5
IMPORTANT: The engine speed parameter must stabilize after each commanded change.
  1. Start the engine.
  2. Allow the engine to reach operating temperature.
  3. Allow the engine to idle.
  4. Turn OFF all accessories.
  5. Command the idle air control (IAC) valve to increase engine speed to 1,700 RPM and then decrease engine speed to 500 RPM with the scan tool RPM control function.
Is the engine speed within the specified value of the commanded RPM at each increment?		 100 RPM Go to Intermittent Conditions Go to Idle Air Control (IAC) System Diagnosis
6 Inspect the throttle body for the following conditions:
  • Throttle blade binding or damaged
  • Cruise control cable binding or damaged
  • Throttle cable binding or damaged

Did you find and correct the condition?		 - Go to Step 15  Go to Step 7 
7 Test for an intermittent and for a poor connection at the throttle position (TP) sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 15  Go to Step 8 
8 
  1. Disconnect the TP sensor harness connector.
  2. Measure the voltage from the 5-volt reference circuit of the TP sensor to a good ground, with a DMM. Note the measurement as Supply Voltage.
  3. Connect test lamp and a DMM in series between the 5-volt reference and the low reference circuit of the TP sensor at the harness connector.
  4. Measure the amperage with the DMM. Note the measurement as Amperage.
  5. Remove the DMM from the circuit.
  6. Connect the test lamp between the 5-volt reference circuit and the low reference circuit of the TP sensor, at the harness connector.
    7. IMPORTANT: Before any calculations are performed, ensure that all measurements are converted to like units. For example, volts/lamps or millivolts/milliamps.
  7. Measure the voltage from the 5-volt reference circuit at the test lamp to a good ground, with the DMM. Note the measurement as Load Voltage Drop.
  8. Subtract the Load Voltage Drop from the Supply Voltage. Note the result as Supply Voltage Drop.
  9. Divide the Supply Voltage Drop by the Amperage.
Is the result more than the specified value?		 5 Ω Go to Step 10  Go to Step 9 
9 
IMPORTANT: Before any calculations are performed, ensure that all measurements are converted to like units. For example, volts/lamps or millivolts/milliamps.
  1. Measure the voltage from the low reference circuit of the TP sensor at the test lamp to a good ground, with the DMM. Note the result as Low Reference Voltage Drop.
  2. Divide the Low Reference Voltage Drop by the Amperage.
Is the result more than the specified value?		 5 Ω Go to Step 11  Go to Step 13 
10 Test the 5-volt reference circuit between the powertrain control module (PCM) and the TP sensor for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 15  Go to Step 12 
11 Test the low reference circuit between the PCM and the TP sensor for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 15  Go to Step 12 
12 Test for an intermittent and for a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 15  Go to Step 14 
13 Replace the TP sensor. Refer to Throttle Position (TP) Sensor Replacement .
Did you complete the replacement?		 - Go to Step 15  -
14 Replace the PCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.
Did you complete the replacement?		 - Go to Step 15  -
15
  1. Clear the DTCs with a scan tool.
  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.
Did the DTC fail this ignition?		 - Go to Step 2  Go to Step 16 
16 Observe the Capture Info with a scan tool.
Are there any DTCs that have not been diagnosed?		 - Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information System OK
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