GM Service Manual Online
For 1990-2009 cars only

Object Number: 369636  Size: LF
Engine Controls Components
Ground for TAC Module
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The Throttle Position (TP) sensor is mounted on the throttle body/TAC assembly. The sensor is actually two individual Throttle Position sensors within one housing. Two separate signal, ground and reference circuits are used in order to connect the TP sensor assembly and the Throttle Actuator Control (TAC) Module. Each TP sensor signal voltage increases as the throttle opens. The signal circuit for TP Sensors are pulled up to reference voltage.

Conditions for Running the DTC

    • DTCs P0606, P1517, P1518 are not set.
    • The ignition switch is in the crank or run position.
    • The ETC serial data is operational.

Conditions for Setting the DTC

    • TP sensor 1 and TP sensor 2 disagree by more than 0.17 volts.
    • All of the above conditions met for less than 1 second.

Action Taken When the DTC Sets

    • The PCM will illuminate the malfunction indicator lamp (MIL) during the first trip in which the diagnostic runs and fails.
    • If equipped with traction control, the PCM will command the EBTCM via the serial data circuit to turn OFF traction control and illuminate the TRACTION OFF lamp.
    • The PCM will store conditions which were present when the DTC set as Freeze Frame and Fail Records data.

Conditions for Clearing the MIL/DTC

    • The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been run and passed.
    • The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
    • The DTC can be cleared by using the scan tool.

Diagnostic Aids

Important: Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing/replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminant intrusion.

    • The following may cause an intermittent:
       - Poor connections. Check for adequate terminal tension. Refer to Wiring Repairs for proper procedure.
       - Corrosion
       - Mis-routed harness.
       - Rubbed through wire insulation.
       - Broken wire inside the insulation.
       - Inspect the connector for signs of water intrusion. When this occurs, multiple DTCs should be set and no circuit or component problems can be located.
    • For an intermittent, refer to Symptoms .
    • If a repair is completed and the DTC was cleared using a scan tool on the same ignition cycle, the default action will not clear until an ignition cycle has occurred.
    • When the TAC module detects a problem within the ETC System the PCM receives a message across serial data and more than one ETC System related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing one individual problem may correct more than one DTC. Keep this in mind when reviewing captured DTC info.

Test Description

The numbers below refer to the step numbers on the Diagnostic Table.

  1. When the TAC module detects a problem within the ETC System the PCM receives a message across serial data and more than one ETC System related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing one individual problem may correct more than one DTC. Keep this in mind when reviewing captured DTC info.

DTC P1221 - Throttle Position (TP) Sensor 1, 2 Performance

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Important: If DTC P1518, 1120 or 1220 are also set, refer to those DTCs first for further diagnosis.

  1. Turn ON the ignition, with the engine OFF.
  2. With a scan tool, observe the TP Disagree parameter.

Does the scan tool indicate NO?

--

Go to Step 3

Go to Step 4

3

  1. With a scan tool, select Diagnostic Trouble Code (DTCs).
  2. Move the harness and related connectors while observing the DTC information.

Does the harness movement cause this DTC to fail this ignition?

--

Go to Step 10

Go to Diagnostic Aids

4

  1. Turn OFF the ignition.
  2. Disconnect the TAC.
  3. Turn ON the ignition.
  4. Measure the voltage on both the TP 1 and TP 2 reference circuits using a J 39200 Digital Multimeter that is connected to a good ground.

Does the voltage measure within the specified range?

3.9-4.6 V

Go to Step 5

Go to Step 11

5

Measure the voltage on both the TP 1 and TP 2 signal circuits using a DMM that is connected to a good ground.

Does the voltage measure within the specified range?

3.9-4.6 V

Go to Step 6

Go to Step 12

6

Measure for continuity between the TP 1 reference and the TP 2 reference at the TAC using a DMM.

Does the DMM indicate continuity?

--

Go to Step 13

Go to Step 7

7

Measure for continuity between the TP 1 signal and the TP 2 signal at the TAC using a DMM.

Does the DMM indicate continuity?

--

Go to Step 13

Go to Step 8

8

  1. Disconnect the TAC Module.
  2. Leave the TAC disconnected.
  3. Measure for continuity between the TP 1 reference and the TP 2 reference at the TAC Module harness connector using a DMM.

Does the DMM indicate continuity?

--

Go to Step 15

Go to Step 9

9

Measure for continuity between the TP 1 signal and the TP 2 signal at the TAC Module harness connector using a DMM.

Does the DMM indicate continuity?

--

Go to Step 16

Go to Step 14

10

Repair the harness/connections as necessary. Refer to Wiring Repairs and Connector Repairs .

Did you complete the repair?

--

Go to Step 17

--

11

Repair the short to voltage in the reference circuit. Refer to Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 17

Go to Step 14

12

Repair the short to voltage in the signal circuit. Refer to Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 17

Go to Step 14

13

Replace the throttle body/TAC assembly. Refer to Throttle Body Assembly Replacement .

Did you complete the replacement?

--

Go to Step 17

--

14

Replace the TAC Module. Refer to Accelerator Pedal Replacement .

Did you complete the replacement?

--

Go to Step 17

--

15

Repair the TP 1 and TP 2 reference circuits shorted together. Refer to Wiring Repairs .

Did you complete the repair?

--

Go to Step 17

--

16

Repair the TP 1 and TP 2 signal circuits shorted together. Refer to Wiring Repairs .

Did you complete the repair?

--

Go to Step 17

--

17

  1. Use the scan tool in order to record Fail Records and clear the DTCs.
  2. Operate the vehicle within the Fail Records conditions.

Does the DTC reset?

--

Go to Step 2

Go to Step 18

18

Does the scan tool indicate any DTCs set that you have not diagnosed?

--

Go to the applicable DTC table

System OK