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Home >> Chevrolet >> 2001 >> Venture Base, Van Passenger >> Repair and Diagnosis >> External Pages >> Different car >> Section 833 (Engine Controls Diagnostic (DTC P0491 To DTC P2130) -- 5.7L) >> Diagnosis >> DTC P2121 >> 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 numbers below refer to the steps numbers in the diagnostic table.

  1. 2:  This step determines if a communication condition exists.
  2. 5:  This step isolates an internal APP sensor failure. The condition may only occur at a certain accelerator pedal position. Monitoring the APP angles for sensor 2 and sensor 3 is an accurate way of verifying the actual position of the pedal. The APP angles for all 3 sensors should be within a few percentages of each other. When the pedal is at rest, the APP angle for all 3 sensors should be 0 percent. When the pedal is fully depressed, all APP angles should be 100 percent.
  3. 6:  The APP sensor 1 shares a common 5-volt reference circuit with the TP sensor 1. Monitoring the TP sensor 1 voltage aids in diagnosing the APP sensor 5-volt reference and the low reference circuits. If the scan tool displays near 0 volts then the circuits are OK.
  4. 9:  With the TAC module still connected, this test will help determine a short to the signal circuit either within the TAC module or the wiring.
  5. 10:  This step determines whether the TAC module or a shorted circuit is causing the condition.
  6. 19:  When the TAC module detects a condition within the TAC system, more than 1 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 P2121

Step Action Values Yes No
Schematic Reference:  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 U0107 also set? - Go to DTC U0107 Go to Step 3 
3
IMPORTANT: Do not depress the accelerator pedal.
  1. Turn OFF the ignition for 15 seconds.
  2. Start the engine.
  3. Observe the DTC Information, with a scan tool.
Did any other throttle actuator control (TAC) module or accelerator pedal position (APP) sensor DTC set except P1125?		 - Go to Diagnostic Trouble Code (DTC) List Go to Step 4 
4 Observe the APP sensor Agree/Disagree parameters, with a scan tool.
Does the scan tool indicate Disagree for any of the APP Agree/Disagree parameters?		 - Go to Step 6  Go to Step 5 
5 
  1. Turn OFF the ignition.
  2. Turn ON the ignition with the engine OFF.
  3. Observe the APP sensor angles for all 3 APP sensors, with a scan tool.
  4. Slowly depress the accelerator pedal, stopping at 25, 50, 75, and 100 percent.
  5. Slowly release the accelerator pedal, stopping at 75, 50, 25, and 0 percent.
Does the scan tool indicate APP sensor 1 angle within 10.5 percent of the APP sensor 2 angle and APP sensor 1 angle within 13 percent of the APP sensor 3 angle during the above test?		 - Go to Diagnostic Aids Go to Step 6 
6 
  1. Turn OFF the ignition.
  2. Disconnect the APP sensor harness connector.
  3. Connect a fused jumper between the APP sensor 1 5-volt reference circuit and ground.
  4. Turn ON the ignition with the engine OFF.
  5. Observe the throttle position (TP) sensor 1 voltage parameter, with a scan tool.
Does the scan tool indicate TP sensor 1 voltage at the specified value?		 0.0 V Go to Step 7  Go to Step 11 
7
  1. Connect a fused jumper between the APP sensor 1 5-volt reference circuit and the APP sensor 1 low reference circuit.
  2. Observe the TP sensor 1 voltage parameter.
Does the scan tool indicate TP sensor 1 voltage at specified value?		 0.0 V Go to Step 8  Go to Step 12 
8
  1. Connect a fused jumper between the APP sensor 1 signal circuit and the APP sensor 1 5-volt reference circuit.
  2. Observe the APP sensor 1 voltage parameter, with a scan tool.
Does the scan tool indicate APP sensor 1 voltage near the specified value?		 5.0 V Go to Step 14  Go to Step 9 
9  Test for a short between the APP sensor 1 signal circuit and all other APP circuits at the APP sensor harness connector, with a DMM.
Does the DMM indicate a short to another circuit?		 - Go to Step 10  Go to Step 13 
10 
  1. Turn OFF the ignition.
  2. Disconnect both of the TAC module harness connectors.
  3. Test for a short between the APP sensor 1 signal circuit and all other APP circuits at the APP sensor harness connector, with a DMM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 18  Go to Step 15 
11
  1. Turn OFF the ignition.
  2. Disconnect the TAC module harness connector containing the APP circuits.
  3. Test the APP sensor 1 5-volt reference circuit for an open or the high resistance, with a DMM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 18  Go to Step 15 
12
  1. Turn OFF the ignition.
  2. Disconnect the TAC module harness connector containing the APP circuits.
  3. Test the APP sensor 1 low reference circuit for an open or high resistance, with a DMM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 18  Go to Step 15 
13
  1. Turn OFF the ignition.
  2. Disconnect the TAC module harness connector containing the APP circuits.
  3. Test the APP sensor 1 signal circuit for an open or the high resistance, with a DMM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find an open or high resistance?		 - Go to Step 18  Go to Step 15 
14 Inspect for poor connections at the harness connector of the APP sensor. 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 18  Go to Step 16 
15 Inspect for poor connections at the harness connectors of the TAC Module. 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 18  Go to Step 17 
16 Replace the APP sensor assembly. Refer to Accelerator Pedal Position (APP) Sensor Replacement .
Did you complete the replacement?		 - Go to Step 18  -
17 Replace the TAC module. Refer to Throttle Actuator Control (TAC) Module Replacement .
Did you complete the replacement?		 - Go to Step 18  -
18
  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 19 
19  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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