For 1990-2009 cars

### Circuit Description

When the transmission is in Park or Neutral, the Park Neutral Position (PNP) switch closes. The Engine Control Module (ECM) uses the switch in order to enable starter operation.

When the ECM detects an invalid combination of switch signals, then DTC P0850 sets. DTC P0850 is a type C DTC.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0705 Transmission Range (TR) Switch Circuit

### Conditions for Running the DTC

The ignition switch is on.

### Conditions for Setting the DTC

TheECM detects that the PNP switch is not in Park or Neutral while the select lever status indicates park or neutral.

### Conditions for Clearing the MIL/DTC

• | The PCM turns off the MIL after the third consecutive drive trip in which the ECM does not send a MIL illumination request.

• | A scan tool can clear the MIL/DTC.

• | The ECM clears the DTC from ECM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring.

• | The ECM cancels the DTC default actions when the ignition switch is OFF long enough in order to power down the ECM.

### Test Description

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

1. By disconnecting the PNP switch, the ground path for all PNP switch circuits would be removed and the ECM should recognize all circuits as open. The scan tool should display HI for all range signals.

2. This step tests the PNP switch wiring for an open or lack of signal voltage from the ECM.

3. This step tests the PNP switch wiring and the ECM by providing a ground path through a fused jumper wire. When grounded, the scan tool range signal A should change to LOW.

4. This step tests the PNP switch wiring and the ECM by providing a ground path through a fused jumper wire. When grounded, the scan tool range signal B should change to LOW.

5. This step tests the PNP switch wiring and the ECM by providing a ground path through a fused jumper wire. When grounded, the scan tool range signal C should change to LOW.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 |

1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.

Important: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records. Using the Clear Eng./Trans. DTC Info function erases the Freeze Frame and Failure Records from the transmission control module (ECM).

3. Record the DTC Freeze Frame and Failure Records.
4. Clear the DTC.
5. Select PNP Sw. on the scan tool.
6. With a scan tool, observe the PNP Sw. display while selecting each transmission range: P, R, N, D, I, and L.

Does each selected transmission range match the scan tool PNP Switch. display?

--

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3 |

1. Inspect the transaxle range (PNP) switch for the following:

• | Damage

• | Loose or missing mounting hardware

• | Refer to Transmission Range Switch Replacement .

• | Proper adjustment

• | Refer to Transmission Range Switch Adjustment .

2. Inspect the shift cable for the following:

• | Damaged or stretched cable

• | Proper adjustment

• | Refer to Transmission Control Replacement .

Did you find and correct a condition?

--

Go to Step 16

Go to Step 4

4 | With the scan tool, observe the PNP Switch. A/B/C/P display. Does the scan tool PNP Switch. A/B/C/P parameter indicate HI for all range signal states? | -- | Go to Step 13 | Go to Step 5
5 |

1. Turn OFF the ignition.
2. Disconnect the PNP switch 10-way connector.
3. Turn ON the ignition, with the engine OFF.

Does the scan tool PNP Switch. A/B/C/P parameter indicate HI for all range signal states?

--

Go to Step 6

Go to Step 10

6 |

1. Using the DMM and the J 35616 GM-approved terminal test kit, measure the voltage from signal A circuit of the PNP switch 10-way connector to ground.
2. Measure the voltage from signal B circuit of the PNP switch 10-way connector to ground.
3. Measure the voltage from signal C circuit of the PNP switch 10-way connector to ground.
4. Measure the voltage from signal P circuit of the PNP switch 10-way connector to B+.

Does the voltage measure within the specified range at all 4 terminals?

10-12 V

Go to Step 7

Go to Step 11

7 | Connect a fused jumper wire from the PNP switch 10-way connector, signal A circuit, to the ground while monitoring the scan tool PNP Switch. A/B/C/P parameter. When the signal A circuit is jumpered to ground, do any other signal circuits indicate LOW? | -- | Go to Step 12 | Go to Step 8
8 | Connect a fused jumper wire from the PNP switch 10-way connector, signal B circuit, to ground while monitoring the scan tool PNP Switch. A/B/C/P parameter. When the signal B circuit is jumpered to ground, do any other signal circuits indicate LOW? | -- | Go to Step 12 | Go to Step 9
9 | Connect a fused jumper wire from the PNP switch 10-way connector, signal C circuit, to ground while monitoring the scan tool PNP Switch. A/B/C/P parameter. When the signal C circuit is jumpered to ground, do any other signal circuits indicate LOW? | -- | Go to Step 12 | Go to Step 14
10 | Test the signal circuits of the PNP switch that did not indicate HIGH for a short to GND. Refer to Testing for Short to Ground and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 15
11 | Test the signal circuits of the PNP switch that did not indicate proper voltage for an open. Refer to Testing for Continuity and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 15
12 | Test the affected signal circuits of the PNP switch for a shorted together condition. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 15
13 | Test the ground circuit of the PNP switch for an open, or high resistance. Refer to Testing for Continuity and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 14
14 | Replace the PNP switch. Refer to Transmission Range Switch Replacement . Did you complete the replacement? | -- | Go to Step 16 | --
15 | Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 16 | --
16 | Perform the following procedure in order to verify the repair:

1. Select DTC.
2. Select Clear Info.
3. Road test the vehicle.
4. Select Specific DTC.
5. Enter DTC P0850.

Does the DTC reset?

--

Go to Step 2

Go to Step 17

17 | With the scan tool, observe the stored information, capture info and DTC info. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle | System OK