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Home >> Chevrolet >> 2006 >> Chevy Express G2500, Van Cargo Extended, 4.3 X, 4L60E/M30 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System - 4.3L - DTC P0016 To DTC P0138 >> DTC P0121 >> Test Description

Test Description

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

  1. 12:  This step calculates the resistance in the 5-volt reference circuit.
  2. 13:  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
2 Inspect for the following conditions:
  • Vacuum hoses disconnected, damaged, or incorrectly routed
  • Manifold absolute pressure (MAP) sensor seal missing or damaged
  • Restrictions in the MAP sensor vacuum source
  • Intake manifold vacuum leaks

Did you find and correct the condition?		 - Go to Step 20  Go to Step 3 
3
IMPORTANT: The vehicle used for the comparison is not limited to the same type of vehicle as is being serviced. A vehicle known to provide an accurate reading is acceptable.
Do you have access to another vehicle in which the MAP sensor pressure can be observed with a scan tool?		 - Go to Step 4  Go to Step 5 
4
  1. Turn ON the ignition, with the engine OFF.
  2. Observe the MAP sensor pressure with a scan tool.
  3. Observe the MAP sensor pressure in the known good vehicle with a scan tool.
  4. Compare the values.
Is the difference between the values less than the specified value?		 3 kPa Go to Step 6  Go to DTC P0106 
5
IMPORTANT: The Altitude vs. Barometric Pressure table indicates a pressure range for a given altitude under normal weather conditions. Weather conditions consisting of very low or very high pressure and/or very low or very high temperature may cause a reading to be slightly out of range.
  1. Turn ON the ignition, with the engine OFF.
  2. Observe the MAP sensor pressure with a scan tool. Refer to Altitude vs Barometric Pressure .
  3. The MAP sensor pressure should be within the range specified for your altitude.
Does the MAP sensor indicate the correct barometric pressure (BARO)?		 - Go to Step 6  Go to DTC P0106 
6
  1. Observe the MAP sensor pressure with a scan tool.
  2. Start the engine.
Does the MAP sensor pressure change?		 - Go to Step 7  Go to DTC P0106 
7
  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 8  Go to Step 9 
8
  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 Testing for Intermittent Conditions and Poor Connections Go to Step 10 
9 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 20  Go to Step 10 
10 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 .
Did you find and correct the condition?		 - Go to Step 20  Go to Step 11 
11
  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 a 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".
Is the amperage equal to the specified value?		 0 mA Go to Step 15  Go to Step 12 
12 
  1. Remove the DMM from the circuit.
  2. Connect the test lamp between the 5-volt reference circuit and the low reference circuit of the TP sensor, at the harness connector.
  3. 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".
    4. IMPORTANT: Before any calculations are performed, ensure that all measurements are converted to like units, for example, volts/amps or millivolts/milliamps.
  4. Subtract the "load voltage drop" from the "supply voltage". Note the result as "supply voltage drop".
  5. Divide the "supply voltage drop" by the "amperage".
Is the result more than the specified value?		 5 Ω Go to Step 14  Go to Step 13 
13 
  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. IMPORTANT: Before any calculations are performed, ensure that all measurements are converted to like units, for example, volts/amps or millivolts/milliamps.
  2. Divide the "low reference voltage drop" by the "amperage".
Is the result more than the specified value?		 5 Ω Go to Step 16  Go to Step 18 
14 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 .
Did you find and correct the condition?		 - Go to Step 20  Go to Step 17 
15 Test the low reference circuit between the PCM and the TP sensor for an open. Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?		 - Go to Step 20  Go to Step 17 
16 Test the low reference circuit between the PCM and the TP sensor for high resistance. Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?		 - Go to Step 20  Go to Step 17 
17 Test for an intermittent and for a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?		 - Go to Step 20  Go to Step 19 
18 Replace the TP sensor. Refer to Throttle Position (TP) Sensor Replacement .
Did you complete the replacement?		 - Go to Step 20  -
19 Replace the PCM. Refer to Control Module References for replacement, setup, and programming.
Did you complete the replacement?		 - Go to Step 20  -
20
  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 21 
21 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 System OK
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