GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2008 🢒 Vibe - FWD 🢒 Safety and Security 🢒 Supplemental Inflatable Restraints 🢒 DTC P1780

Circuit Description

The powertrain control module (PCM) determines when the vehicle is in Park or Neutral gear position through the park/neutral position (PNP) switch. The RD/BK wire to the PCM is grounded by the PNP switch when the transmission manual selector is in either Park or Neutral gear position.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1780 Park/Neutral Position (PNP) Switch Circuit

Conditions for Setting the DTC
    • Engine speed changed from below 300 RPM to over 500 RPM when the vehicle speed is 0 km/h (0 mph) and the PNP switch is open--R, D, 2 or L gear positions.
    • The PNP switch closed/P or N gear position is detected for 10 seconds while the engine is running at over 2,500 RPM and with more than 38.5 percent calculated load value.

Action Taken When the DTC Sets

The malfunction indicator lamp (MIL) will illuminate with the fault active.

Conditions for Clearing the DTC
    • The MIL will turn OFF after 3 consecutive drive cycles without a fault present.
    • DTC will clear after 40 consecutive warm-up cycles without a fault.
    • DTC can be cleared by using a scan tool or by disconnecting the PCM battery feed.

Diagnostic Aids

Inspect for the following conditions:

    • The PNP switch, for proper operation
    • Poor connection at the PCM connector C3, the PNP switch connector, and at connector CZ10. Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal-to-wire connection.
    • Damaged harness--Inspect the wiring harness for damage.
    • If DTC P1780 cannot be duplicated, the information included in the freeze frame data can be useful in determining vehicle operating conditions since the DTC was last set. This may assist in determining how often the DTC sets.

DTC Confirmation Procedure

The DTC Confirmation Procedure outline is here as follows:

  1. Turn the ignition switch to LOCK.
  2. Connect the scan tool to data link connector (DLC).
  3. Start engine and warm-up to normal operating temperature.
  4. Use a scan tool in order to clear the following items from the PCM memory:
    5. • The DTC
    • The pending DTC
    • Freeze frame data
  5. Drive the vehicle to 43 km/h (27 mph) in Drive range for 10 seconds.
  6. Accelerate the vehicle to 85 km/h (53 mph) in Drive range for 10 seconds.
  7. Stop the vehicle.
  8. Use the scan tool in order to inspect for DTC P1780.

Test Description

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

  1. The Diagnostic System Check - Vehicle, prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

  2. This step checks the L position signal circuit.

    3.

  3. This step checks the N and the P position signal circuit.

    4.

  4. This step checks the P position signal circuit.

    5.

  5. This step checks the R position signal circuit.

    6.

  6. This step checks for poor terminal contact at the PCM.

    7.

  7. This step checks for a faulty PCM.

    8.

  8. This step checks for a short to voltage in the L position.

    9.

  9. This step checks for a short to ground in the L position.

    10.

  10. This step checks for an open in the L position.

    11.

  11. This step checks for a short to voltage in the N and P positions.

    12.

  12. This step checks for a short to ground in N and P positions.

    13.

  13. This step checks for an open in N and P positions.

    14.

  14. This step checks for a short to voltage in the 2 position.

    15.

  15. This step checks for a short to ground in the 2 position.

    16.

  16. This step checks for an open in the 2 position.

    17.

  17. This step checks for a short to voltage in R position.

    18.

  18. This step checks for a short to ground in R position.

    19.

  19. This step checks for an open in R position.

Step

Action

Values

Yes

No

Schematic Reference: Automatic Transmission Controls Schematics

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  1. Install a scan tool.
  2. Turn the ignition to ON, leaving the engine OFF.
  3. Perform the scan tool Clear DTC Information function.
  4. Operate the vehicle within the Freeze Frame conditions as observed.

Does the scan tool display any other DTCs in addition to DTC P1780?

--

Go to the applicable DTC table

Go to Step 3

3

  1. Turn the ignition switch to LOCK.
  2. Disconnect powertrain control module (PCM) connector C3.
  3. Turn ignition switch to ON.
  4. Using the DMM measure voltage between ground and PCM harness connector C3, terminal 8 while shifting the manual selector from Park to Low gear.

Is the voltage within the range specified?

10-14 V in Low gear

0-2 V in all other gears

Go to Step 5

Go to Step 10

4

Using the DMM measure voltage between ground and the PCM harness connector C3, terminal 11 while shifting the manual selector from Low to Neutral gear and Park gear.

Is the voltage within the range specified?

10-14 V in Neutral and Park gears

Go to Step 5

Go to Step 13

5

Using the DMM measure the voltage between ground and the PCM harness connector C3, terminal 9 while shifting the manual selector from Park to 2nd gear.

Is the voltage within the range specified?

10-14 V in 2nd gear

Go to Step 6

Go to Step 16

6

Using the DMM measure the voltage between ground and the PCM harness connector  C3, terminal 11 while shifting the manual selector from 2nd to Reverse gear.

Is the voltage within the range specified?

10-14 V in Reverse gear

Go to Step 7

Go to Step 19

7

Inspect the PCM harness connector C3 for poor terminal contact.

Is poor terminal evident?

--

Go to Step 23

Go to Step 8

8

  1. Shift the manual selector to Park gear.
  2. Turn the ignition switch to LOCK.
  3. Install a good known PCM. Refer to Powertrain Control Module Programming and Setup .
  4. Perform the DTC Confirmation Procedure.

Does the DTC reset?

--

Go to Step 24

Go to Step 22

9

  1. Turn the ignition switch to LOCK.
  2. Disconnect the park/neutral position (PNP) switch electrical connector.
  3. Turn the ignition switch to ON.
  4. Using the DMM measure the voltage between ground and the PCM harness connector C3, terminal 19.

Is the voltage within the range specified?

1-2 V

Go to Step 10

Go to Step 27

10

Using the DMM measure the resistance between ground and the PCM harness connector C3, terminal 19.

Is the resistance equal to the value specified?

∞

Go to Step 11

Go to Step 28

11

Using the DMM measure the resistance between PCM harness connector C3, terminal 19 and the PNP switch connector terminal 6 - harness side.

Is the resistance less than the value specified?

2 ohms

Go to Step 12

Go to Step 29

12

Using the DMM measure the voltage between ground and PNP switch connector terminal 4 - harness side.

Is the voltage within the range specified?

10-14 V

Go to Step 25

Go to Step 26

13

  1. Turn ignition switch to LOCK.
  2. Disconnect PNP switch electrical connector.
  3. Turn ignition switch to ON.
  4. Using the DMM measure voltage between ground and PCM harness connector C3, terminal 11.

Is the voltage within the range specified?

1-2 V

Go to Step 14

Go to Step 30

14

Using the DMM measure the resistance between ground and the PCM harness connector C3, terminal 11.

Is the resistance equal to the specified value?

∞

Go to Step 15

Go to Step 31

15

Using the DMM measure the resistance between the PCM harness connector C3, terminal 11 and the PNP switch connector terminal 3 - harness side.

Is the voltage equal to the specified value?

2 ohms

Go to Step 12

Go to Step 32

16

  1. Turn the ignition switch to LOCK.
  2. Disconnect the PNP switch electrical connector.
  3. Turn the ignition switch to ON.
  4. Using the DMM measure the voltage between ground and PCM harness connector C3, terminal 18.

Is the voltage within the range specified?

1-2 V

Go to Step 17

Go to Step 33

17

Using the DMM measure the resistance between ground and PCM harness connector C3, terminal 18.

Is the resistance equal to the value specified?

∞

Go to Step 18

Go to Step 34

18

Using the DMM measure the resistance between the PCM harness connector C3, terminal 18 and the PNP switch connector terminal 5 - harness side.

Is the resistance less than the value specified?

2 ohms

Go to Step 12

Go to Step 35

19

  1. Turn the ignition switch to LOCK.
  2. Disconnect the PNP switch electrical connector.
  3. Turn the ignition switch to ON.
  4. Using the DMM measure the voltage between ground and the PCM harness connector C3, terminal 17.

Is the voltage within the range specified?

1-2 V

Go to Step 20

Go to Step 36

20

Using the DMM measure the resistance between ground and the PCM harness connector C3, terminal 17

Is the resistance equal to the value specified?

∞

Go to Step 21

Go to Step 37

21

Using the DMM measure the resistance between the PCM harness connector C3, terminal 17 and the PNP switch connector terminal 8 - harness side.

Is the resistance less than the value specified?

2 ohms

Go to Step 12

Go to Step 38

22

Refer to Diagnostic Aids for a possible intermittent condition. If OK, replace the PCM. Refer to Powertrain Control Module Programming and Setup .

Is the action complete?

--

Go to Step 39

--

23

Repair the terminal that exhibits poor contact.

Is the action complete?

--

Go to Step 39

--

24

Refer to Diagnostic Aids for additional information regarding this DTC.

Is the action complete?

--

Go to Step 39

--

25
  1. Inspect the PNP switch for proper alignment.
  2. If OK, replace the PNP switch.

Is the action complete?

--

Go to Step 39

--

26

Repair the open or high resistance in RD/WH wire between the PNP switch and GAGE fuse. Refer to Testing for Intermittent Conditions and Poor Connections .

Is the action complete?

--

Go to Step 39

--

27

Repair the short to voltage in L-GN wire between the PNP switch and the PCM.

Is the action complete?

--

Go to Step 39

--

28

Repair the short to ground in L-GN wire between the PNP switch and the PCM.

Is the action complete?

--

Go to Step 39

--

29

Repair the open or high resistance in L-GN wire between the PNP switch and the PCM.

Is the action complete?

--

Go to Step 39

--

30

Repair the short to voltage in L-GN/BK wire between the PNP switch and the PCM.

Is the action complete?

--

Go to Step 39

--

31

Repair the short to ground in L-GN/BK wire between PNP switch and the PCM.

Is the action complete?

--

Go to Step 39

--

32

Repair the open or high resistance in L-GN/BK wire between PNP switch and the PCM.

Is the action complete?

--

Go to Step 39

--

33

Repair the short to voltage in RD/BK wire between the PNP switch and the PCM.

Is the action complete?

--

Go to Step 39

--

34

Repair the short to ground in RD/BK wire between the PNP switch and the PCM.

Is the action complete?

--

Go to Step 39

--

35

Repair the open and high resistance in RD/BK wire between the PNP switch and the PCM.

Is the action complete?

--

Go to Step 39

--

36

Repair the short to voltage in BK wire between the PNP switch and the PCM.

Is the action complete?

--

Go to Step 39

--

37

Repair the short to ground in BK wire between the PNP switch and the PCM.

Is the action complete?

--

Go to Step 39

--

38

Repair the open or high resistance in BK wire between the PNP switch and the PCM.

Is the action complete?

--

Go to Step 39

--

39
  1. Turn the ignition switch to LOCK.
  2. Reconnect the connectors.
  3. Perform the DTC confirmation procedure.

Are any DTCs displayed on the scan tool?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK