GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2008 🢒 Silverado - 4WD 🢒 DTC 🢒 DTC P0872

Circuit Description

The pressure switch manifold (PSM) is a multiple-switch assembly made up of 3 normally open (N/O) pressure switches and 1 normally closed (N/C) pressure switch. Pressure switch 3 (PS3) monitors shift valve 3 positioning and relays it to the transmission control module (TCM).

DTC P0872 is a type A DTC.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0872 Transmission Pressure Switch 3 Circuit Low

Conditions for Running the DTC
    • The components are powered and ignition voltage is greater than 9.0 volts and less than 18 volts.
    • Engine speed is greater than 200 RPM and less than 7,500 RPM for 5 seconds.
    • Shift valve 3 is commanded to the OFF, destroked, position.

Conditions for Setting the DTC

DTC P0872 sets when PS3 indicates ON for 20 milliseconds after shift solenoid 3 (SS3) has been commanded OFF.

Action Taken When the DTC Sets
    • The TCM illuminates the malfunction indicator lamp (MIL).
    • When in a forward range, the transmission will fail to another forward range, unless the transmission is compromised by overspeeding or direction change, then the transmission will shift to NEUTRAL while diagnostic response is active.
    • If the shift selector is moved from a forward range to NEUTRAL or from a forward range to REVERSE, then the transmission will shift to NEUTRAL.
    • If the shift selector is moved to REVERSE, the transmission will shift to REVERSE if it is not compromised by overspeeding or a direction change. If compromised, the transmission will shift to NEUTRAL.
    • DTC P0872 is stored in TCM history.
    • The TCM freezes shift adapts.
    • The TCM inhibits torque converter clutch (TCC) engagement.

Conditions for Clearing the DTC

A scan tool can clear the code from TCM history. The TCM automatically clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without failure.

Diagnostic Aids
    • Inspect the wiring for poor electrical connections at the TCM. Inspect for the following conditions:
       - A bent terminal
       - A backed-out terminal
       - A damaged terminal
       - Poor terminal tension
       - A chafed wire
       - A broken wire inside the insulation
    • When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.
    • You may have to drive the vehicle in order to experience a condition.
    • When DTC P0762 and P0872 are set in combination, this may indicate a short to ground is present at the pressure switch circuit.
    • This DTC may indicate that SS3 is mechanically defective.
    • This DTC can be set by a loss of prime.

Test Description

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

  1. This step tests the TCM response function.

    2.

  2. This step tests the transmission wiring harness integrity.

    3.

  3. This step tests and evaluates the internal wiring harness.

    4.

  4. This step tests the PSM for a failed condition.

Step

Action

Yes

No

Schematic Reference: Automatic Transmission Controls Schematics

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

Measure the transmission fluid level. Refer to Transmission Fluid Check .

Is the transmission fluid level correct?

Go to Step 3

Go to Transmission Fluid Check

3

Measure line pressure. Refer to Line Pressure Check .

Is the pressure within the specified value?

Go to Step 4

Go to Symptoms - Automatic Transmission

4
  1. Install the scan tool.
  2. Turn ON the ignition, with the engine OFF.

    3. Important: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records for reference. The Clear Info function will erase the data.

  3. Record the DTC Freeze Frame and Failure Records.
  4. Clear the DTC.
  5. Start the engine.
  6. Using the scan tool, monitor PS3 status.

Does the scan tool indicate PS3 status is LOW?

Go to Diagnostic Aids

Go to Step 5

5

  1. Turn the ignition OFF.
  2. Disconnect the 80-way connector at the TCM.
  3. Install the J 39700 breakout box, the J-47275 breakout box adapter and the J 47275-1 magnetic overlay.
  4. Turn ON the ignition, with the engine OFF.
  5. Connect terminal 57 to ground.

Does the scan tool indicate PS3 status is LOW when grounded and HIGH when open?

Go to Step 6

Go to Step 12

6

  1. Turn the ignition OFF.
  2. Disconnect the AT inline 20-way connector. Additional DTCs may set.
  3. Install the J 44152 jumper harness (20 pins) on the engine side of the AT inline 20-way connector.
  4. Turn ON the ignition, with the engine OFF.
  5. Using the J 35616 GM terminal test kit and a fused jumper wire, connect terminal E of the J 44152 to ground. Refer to Inline Harness Connector End Views .

Does the scan tool indicate PS3 status is LOW when grounded and HIGH when open?

Go to Step 7

Go to Step 11

7

  1. Connect the AT inline 20-way connector.
  2. Remove the transmission oil pan. Refer to Oil Pan Replacement .
  3. Disconnect the AT internal wiring harness from the PSM and ground terminal C.

Does the scan tool indicate PS3 status is LOW when grounded and HIGH when open?

Go to Step 8

Go to Step 10

8

  1. Remove the PSM from the control valve body and leave the AT internal harness connected. Refer to Pressure Switch Manifold Replacement .
  2. Provide a ground connection for the PSM to either the control valve body or the transmission main case.
  3. Using the eraser end of a pencil, push gently on the PS3 membrane.

Does the scan tool indicate PS3 status is LOW when depressed and HIGH when open?

Go to Diagnostic Aids

Go to Step 9

9

Replace the PSM. Refer to Pressure Switch Manifold Replacement .

Did you complete the replacement?

Go to Step 13

--

10

Replace the AT internal wiring harness. Refer to Wiring Harness Replacement .

Did you complete the replacement?

Go to Step 13

--

11

Test the PS3 circuit between the TCM and AT inline 20-way connector for an open or short condition. Refer to Circuit Testing .

Did you find and correct the condition?

Go to Step 13

--

12

Important: Prior to replacing the TCM, swap the TCM with a known good TCM. In most cases, the TCM is not at fault. Investigate thoroughly before replacing the TCM.

Replace the TCM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 13

--

13

Perform the following procedure in order to verify the repair:

  1. Clear the DTC.
  2. Start the engine.
  3. Using the scan tool, monitor PS3 status.
  4. Select Specific DTC.
  5. Enter DTC P0872.

Has the test run and passed?

Go to Step 14

Go to Step 2

14

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