GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2001 🢒 Prizm 🢒 Transmission/Transaxle 🢒 Automatic Transmission - 3 Speed-MB3 🢒 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 PCM is grounded by the PNP switch when the transmission manual selector is in either Park or Neutral gear position.

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 2500 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 connections at the PCM connectors, the PNP switch connector. 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 number(s) below refer to the step number(s) on the diagnostic table.

  1. The Powertrain OBD System Check 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.

  2. This step checks the PNP switch for proper alignment.

    3.

  3. This step checks for voltage at the PCM connector.

    4.

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

    5.

  5. This step checks for a faulty PCM.

    6.

  6. This step checks for an intermittent condition.

Step

Action

Value(s)

Yes

No

Schematic Reference: Automatic Transmission Controls Schematics

1

Was the On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check - Automatic Transmission in Engine Controls

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

Inspect the PNP switch for proper alignment.

Is the PNP switch aligned properly?

--

Go to Step 4

Align PNP switch. Refer to Park/Neutral Position Switch Replacement

4

  1. Turn the ignition switch to LOCK.
  2. Disconnect PCM connector C1.
  3. Turn ignition switch to ON.
  4. Measure voltage between ground and PCM harness connector C1, terminal 19.

Is the voltage within the range specified?

9-14 V

Go to Step 5

Refer to Circuit Testing

5

Measure voltage between ground and the PCM harness connector C3, terminal 11 with the manual selector in Neutral gear and Park gear.

Is the voltage within the range specified?

9-14 V in Neutral and Park gears

Go to Step 6

Go to Step 7

6

Inspect the PCM harness connectors C1 and  C3 for poor terminal contact.

Is poor terminal evident?

--

Repair terminals as necessary

Go to Step 10

7

Measure the voltage between ground and the PNP connector terminal 9.

Is the voltage within the range specified?

9-14 Volts

Go to Step 8

Refer to Circuit Testing

8

Replace the PNP switch.

Does the system function correctly?

--

Go to Step 11

Go to Step 9

9

Refer to Diagnostic Aids for a possible intermittent condition.

Is the action complete?

--

Go to Step 11

Go to Step 10

10

  1. Shift the manual selector to Park gear.
  2. Turn the ignition switch to LOCK.
  3. Install a good known PCM.

Does the DTC reset?

--

Go to Step 2

System OK

11

Perform the DTC confirmation procedure.

Are any DTCs displayed on the scan tool?

--

Go to Applicable DTC Table

System OK