GM Service Manual Online
For 1990-2009 cars only
Table 1: APP Sensor Position Table

Circuit Description

The accelerator pedal position (APP) sensor is mounted on the accelerator pedal assembly. The sensor is actually 3 individual APP sensors within 1 housing. Three separate signal, low-reference and 5-volt reference circuits connect the APP sensor assembly to the throttle actuator control (TAC) module. Each sensor has a unique functionality.

The throttle position (TP) sensor 1 and APP sensor 1 share a 5-volt reference circuit that are connected within the TAC module. TP sensor 2 and APP sensor 2 share a 5-volt reference circuit that are connected within the TAC module. If only 1 APP sensor DTC is set, the redundant APP systems allow the TAC system to continue operating normally. One APP sensor DTC will not cause the Reduced Engine Power message to be displayed. Two APP sensor DTCs for the same sensor also will not cause the Reduced Engine Power message to be displayed. If an out of range condition is detected with this APP sensor, this DTC will be set.

The table below shows the percentage and voltage readings of the scan tool based on the position of the APP.

APP Sensor Position Table

APP Sensor

Actual Pedal Position

% Depressed as Observed on a Scan Tool

Voltage as Observed on a Scan Tool

1

Pedal at rest

0

Below 1.0

1

Pedal at full travel

100

Above 2.0

2

Pedal at rest

0

Above 4.0

2

Pedal at full travel

100

Below 2.9

3

Pedal at rest

0

Above 3.8

3

Pedal at full travel

100

Below 3.1

Conditions for Running the DTC

    • DTCs  P0601, P0602, P0606, P1517, or P1518 are not set.
    • The ignition switch is in the crank or run position.
    • The ignition voltage is greater than 5.23 volts.

Conditions for Setting the DTC

    • The APP sensor 2 voltage is less than 0.83 volt or greater than 4.81 volts.
    • All of the above conditions are present for less than 1 second.

Action Taken When the DTC Sets

    • The control module stores the DTC information into memory when the diagnostic runs and fails.
    • The malfunction indicator lamp (MIL) will not illuminate.
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.
    • If one or more APP sensor DTCs are set for a single APP sensor, the following occurs:
       - The control module will not command Reduced Engine Power mode.
       -  The control module will use the remaining two APP sensors to calculate throttle response.
    • If certain multiple APP sensor DTCs are set for more than one APP sensor, the following occurs:
       - The control module commands Reduced Engine Power mode.
       - The APP indicated angle is limited to a predetermined value to limit the amount of throttle control.
       - The message center displays Reduced Engine Power.
    • If all three APP sensors are out of range, the following occurs:
       - The control module commands Reduced Engine Power mode.
       - The APP indicated angle is limited to 0 percent. The control module only allows the engine to idle.
       - The message center displays Reduced Engine Power.

Conditions for Clearing the DTC

    • A current DTC Last Test Failed clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
    • Clear the DTC with a scan tool.

Diagnostic Aids

    • Inspect the TAC module connectors for signs of water intrusion. If water intrusion occurs, multiple DTCs may set without any circuit or component conditions found during diagnostic testing.
    • When the TAC module detects throttle movement with a DTC P1280 set, a DTC P1281 also sets.
    • 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 run continuously on this system. Locating and repairing 1 individual condition may correct more than 1 DTC. Disconnecting components during testing may set additional DTCs. Remember this if you review the stored information in Capture Info.
    • For an intermittent, refer to Intermittent Conditions .

Test Description

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

  1. TP sensor 2 and the APP sensor 2 share a common 5-volt reference source. Diagnosis DTC P1220 first if P1220 is also set.

  2. This test determines whether or not the TAC module can recognize a change in signal voltage.

  3. There are 3 separate 5-volt reference sources within the TAC module. TP sensor 1 and APP sensor 1 share 1 5-volt reference source, TP sensor 2 and APP sensor 2 share another common 5-volt reference source and APP sensor 3 uses the third by itself. This test determines whether the signal circuit is shorted to any 1 of the 5-volt reference circuits. If a short exists, the corresponding sensor voltage will be pulled low.

  4. The previous step found the signal circuit and a 5-volt reference circuit shorted together. This test isolates whether the short is in the harness or within the TAC module.

  5. 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 run continuously on this system. Locating and repairing 1 individual condition may correct more than 1 DTC. Disconnecting components during testing may set additional DTCs. Remember this if you review the stored information in Capture Info.

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

Important: If DTCs P1518 or P1220 is also set, refer to Diagnostic Trouble Code (DTC) List and diagnose the applicable DTC first.

  1. Turn ON the ignition, with the engine OFF.
  2. With a scan tool, observe the APP sensor 2 voltage parameter.

Does the scan tool indicate APP sensor 2 voltage within the specified values?

3.90-4.81 V

Go to Step 3

Go to Step 6

3

Fully depress the accelerator pedal to the wide open throttle (WOT) position.

Does the scan tool indicate APP sensor 2 voltage within the specified values?

0.83-2.9 V

Go to Step 4

Go to Step 6

4

  1. Turn OFF the ignition for 15 seconds.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, observe DTC info.
  4. Lightly touch and move the related engine wiring harnesses and connectors for the APP sensor while observing the DTC status.
  5. If the scan tool indicates this DTC failed this ignition during the above test, repair the intermittent condition as necessary. Refer to Wiring Repairs and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 5

5

Slowly depress the accelerator pedal to WOT and then slowly return the pedal to closed throttle while observing the DTC status.

Did the scan tool indicate this DTC failed this ignition during the above test?

--

Go to Step 21

Go to Diagnostic Aids

6

  1. Disconnect the APP sensor harness connector.
  2. With a DMM, test the APP sensor 2 signal circuit for voltage.

Does the DMM indicate APP sensor 2 signal voltage within the specified values?

3.94-6.06 V

Go to Step 11

Go to Step 7

7

  1. Turn OFF the ignition.
  2. Disconnect the TAC module harness connector containing the APP sensor circuits.
  3. Turn ON the ignition, with the engine OFF.
  4. With a DMM, test the APP sensor 2 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 25

Go to Step 8

8

With a DMM, test the APP sensor 2 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 25

Go to Step 9

9

With a DMM, test the APP sensor 2 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 25

Go to Step 10

10

With a DMM, test for a short between the APP sensor 2 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 25

Go to Step 23

11

With a DMM, test the APP sensor 2, 5-volt reference circuit for voltage.

Does the DMM indicate voltage within the specified values?

3.94-6.06 V

Go to Step 16

Go to Step 12

12

  1. Turn OFF the ignition.
  2. Disconnect the TAC module harness connector containing the APP sensor circuits.
  3. Turn ON the ignition, with the engine OFF.
  4. With a DMM, test the APP sensor 2, 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 25

Go to Step 13

13

With a DMM, test the APP sensor 2, 5-volt 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 25

Go to Step 14

14

With a DMM, test the APP sensor 2, 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 25

Go to Step 15

15

With a DMM, test for a short between the APP sensor 2, 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 25

Go to Step 23

16

With a DMM connected between the APP sensor 2 low-reference circuit and the APP sensor 1 low-reference circuit, measure resistance.

Does the DMM indicate resistance within the specified values?

0-5 ohms

Go to Step 18

Go to Step 17

17

  1. Turn OFF the ignition.
  2. Disconnect the TAC module harness connector containing the APP sensor circuits.
  3. With a DMM, test the APP sensor 2 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 25

Go to Step 23

18

  1. Connect a fused jumper between the APP sensor 2 signal circuit and the APP sensor 2 low-reference circuit at the APP sensor harness connector.
  2. With a scan tool, observe the APP sensor 2 voltage parameter

Does the scan tool indicate APP sensor 2 voltage at the specified value?

0 V

Go to Step 19

Go to Step 23

19

  1. With a scan tool, observe the APP sensor 1, APP sensor 3 and TP sensor 2 voltage parameters.
  2. Connect a fused jumper between the APP sensor 2 signal circuit and the APP sensor 2 low-reference circuit at the APP sensor harness connector.

Did the scan tool indicate a change in voltage in any of the parameters observed during the above test?

--

Go to Step 20

Go to Step 21

20

  1. Turn OFF the ignition.
  2. Disconnect the TAC module harness connectors.
  3. With a DMM, test for a short between the APP sensor 2 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 25

Go to Step 23

21

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 25

Go to Step 22

22

Replace the APP sensor assembly. Refer to Accelerator Pedal Position Sensor Replacement .

Did you complete the replacement?

--

Go to Step 25

--

23

Inspect for poor connections at the harness connector 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 25

Go to Step 24

24

Replace the TAC module. Refer to Electronic Throttle Actuator Control Module Replacement .

Did you complete the replacement?

--

Go to Step 25

--

25

  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 26

Go to Step 2

26

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