GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2009 🢒 Sierra - 4WD 🢒 DTC 🢒 DTC P0842, P0847, or P0872

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC P0842: Transmission Fluid Pressure (TFP) Switch 1 Circuit Low Voltage

DTC P0847: Transmission Fluid Pressure (TFP) Switch 2 Circuit Low Voltage

DTC P0872: Transmission Fluid Pressure (TFP) Switch 3 Circuit Low Voltage

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

PS1 Signal

P0752, P0842

P0751, P0843

--

--

PS2 Signal

P0757, P0847

P0756, P0848

--

--

PS3 Signal

P0762, P0872

P0761, P0873

--

--

Typical Scan Tool Data

Display Parameters

Normal Range

Short to Ground

Open/High Resistance

Short to Voltage

Operating Conditions: Ignition ON, engine OFF

TFP Switch 1

High

Low

High

--

TFP Switch 2

High

Low

High

--

TFP Switch 3

High

Low

High

--

Operating Conditions: Engine running, transmission in park or neutral position

TFP Switch 1

Low

Low

High

--

TFP Switch 2

Low

Low

High

--

TFP Switch 3

Low

Low

High

--

Circuit/System 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 1 (PS1) monitors shift valve 1 positioning, Pressure switch 2 (PS2) monitors shift valve 2 positioning, and Pressure switch 2 (PS3) monitors shift valve 3 positioning. The pressure switches communicate the positioning to the transmission control module (TCM).

Conditions for Running the DTC

P0842

    • The engine is running for a minimum of 5 seconds.
    • Ignition voltage is greater than 9.0 V and less than 18 V.
    • Shift valve 1 is commanded to the OFF, or destroked position.

P0847

    • The engine is running for a minimum of 5 seconds.
    • Ignition voltage is greater than 9.0 V and less than 18 V.
    • Shift valve 2 is commanded to the OFF, or destroked position.

P0872

    • The engine is running for a minimum of 5 seconds.
    • Ignition voltage is greater than 9.0 V and less than 18 V.
    • Shift valve 3 is commanded to the OFF, or destroked position.

Conditions for Setting the DTC

P0842

This DTC sets during steady state operation when shift solenoid 1 (SS1) is commanded OFF and PS1 indicates ON for 1 second.

P0847

This DTC sets during steady state operation when shift solenoid 2 (SS2) is commanded OFF and PS2 indicates ON for 1 second.

P0872

This DTC sets during steady state operation when shift solenoid 3 (SS3) is commanded OFF and PS3 indicates ON for 1 second.

Action Taken When the DTC Sets

P0842

    • The TCM requests the engine control module (ECM) to illuminate the malfunction indicator lamp (MIL).
    • When in a forward range and shifting is completed, the transmission will shift 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 shift selector is moved to neutral, the transmission will shift to neutral. If the transmission is shifted to reverse (R), the transmission will shift to REVERSE. If the shift selector is moved to a forward range or reverse and transmission is compromised by overspeeding or direction change, transmission shifts to neutral.
    • DTC P0842 is stored in TCM history.
    • The TCM freezes shift adapts.
    • The TCM inhibits torque converter clutch (TCC) engagement.

P0847

    • The TCM requests the ECM to illuminate the MIL.
    • When in a forward range and shifting is completed, the transmission will shift 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 shift selector is moved to neutral, the transmission will shift to neutral. If the transmission is shifted to reverse (R), the transmission will shift to REVERSE. If the shift selector is moved to a forward range or reverse and transmission is compromised by overspeeding or direction change, transmission shifts to neutral.
    • DTC P0847 is stored in TCM history.
    • The TCM freezes shift adapts.
    • The TCM inhibits TCC engagement.

P0872

    • The TCM requests the ECM to illuminate the MIL.
    • When in a forward range and shifting is completed, the transmission will shift 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 shift selector is moved to neutral, the transmission will shift to neutral. If the transmission is shifted to reverse (R), the transmission will shift to REVERSE. If the shift selector is moved to a forward range or reverse and transmission is compromised by overspeeding or direction change, transmission shifts to neutral.
    • DTC P0872 is stored in TCM history.
    • The TCM freezes shift adapts.
    • The TCM inhibits TCC engagement.

Conditions for Clearing the DTC

DTC P0842, P0847, and P0872 are Type A DTCs.

Diagnostic Aids

P0842

    • You may have to drive the vehicle in order to experience a condition.
    • This DTC may indicate that SS1 is mechanically defective.
    • When DTCs P0752 and P0842 are set in combination, this may indicate a grounded circuit condition on the pressure switch circuit or the shift valve 1 is stuck in the stroked position.

P0847

    • You may have to drive the vehicle in order to experience a condition.
    • This DTC may indicate that SS2 is mechanically defective.
    • When DTCs P0757 and P0847 are set in combination, this may indicate an open circuit condition on the pressure switch circuit or the shift valve 2 is stuck in the stroked position.

P0872

    • You may have to drive the vehicle in order to experience a condition.
    • This DTC may indicate that SS3 is mechanically defective.
    • When DTCs P0762 and P0872 are set in combination, this may indicate an grounded circuit condition on the pressure switch circuit or the shift valve 3 is stuck in the stroked position.

Reference Information

Schematic Reference

Automatic Transmission Controls Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

    •  Transmission General Description
    •  Transmission Component and System Description
    •  Electronic Component Description

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification
  1. Engine running, command the transmission through the forward ranges with a scan tool. Compare the TFP Switch 1, TFP Switch 2, and TFP Switch 3 parameters in each forward range with the Pressure Switch Manifold Logic table. Refer to Pressure Switch Manifold (PSM) Logic.
  2. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

    Note: You must perform the Circuit/System verification first.

  1. Ignition ON, engine OFF, verify with a scan tool the TFP Switch 1, TFP Switch 2 and TFP Switch 3 parameters are High.
    2. ⇒If TFP Switch 1, TFP Switch 2, and TFP Switch 3 parameters are the specified value, refer to Control Valve Body Assembly Disassemble and Control Valve Body Cleaning and Inspection.
    ⇒If valve body inspection is normal, replace the Shift Solenoid indicated by the DTC, refer to Control Valve Solenoid Replacement.
  2. Ignition OFF, disconnect the X175 harness connector at the transmission.
  3. Ignition ON, engine OFF, verify with a scan tool the TFP Switch 1, TFP Switch 2, and TFP Switch 3 parameters are High.
    4. ⇒If not the specified value, test the affected pressure switch signal circuit for a short to ground. If circuits tests normal, replace the TCM.
  4. Remove the transmission oil pan. Refer to Oil Pan Replacement.
  5. Test the transmission internal Pressure Switch 1, 2, and 3 signal circuits for a short to ground.
    6. ⇒If the circuits test normal, replace the PSM. Refer to Pressure Switch Manifold Replacement.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Pressure Switch Manifold Replacement
    •  Control Valve Solenoid Replacement
    •  Control Module References for TCM replacement, setup, and programming.

Repair Verification

If another DTC is present, refer to Diagnostic Trouble Code (DTC) List - Vehicle and perform the appropriate diagnostic procedure.