Has your 3.0L Duramax GM vehicle been shifting gears more roughly than usual? Let’s delve into what might be causing this and how it’s being addressed.

For owners of specific GM models, a rough or harsh transmission shift can be a puzzling and concerning experience. This article will explain the technical background behind this issue, based on a recent TSB (23-NA-102) from General Motors.

Vehicles / Engines Affected:

Identifying the Issue

Owners of various GM models, including Cadillac Escalade, Chevrolet Silverado 1500, Suburban, Tahoe, GMC Sierra 1500, and Yukon models, might experience one or more of the following:

  • Drivability concerns: Issues with engine performance.
  • Hesitation: A lag in response when accelerating.
  • Transmission shifting rough/harsh: An uncomfortable and noticeable change in gear shifts.
  • Malfunction Indicator Lamp (MIL) illuminated: The dashboard alert that something’s not right.

What’s Causing These Symptoms?

This condition could be caused by multiple factors, such as:

  • CAC pump electrical connector issues
  • Active grill shutter electrical connector problems
  • Engine wiring harness contacting the alternator bracket
  • Loose ground at the front of the engine

These issues can result in a range of Diagnostic Trouble Codes (DTCs) being set off. The most common are:

• P1005
• P31C3
• P0700
• U0073
• U0074
• P25A2
• U1600
• U0633
• U0623
• U02A9
• U0285
• U0284
• P10C6
• P2269
• U0074
• U0131
• U029D
• U029E
• U059F
• U18A2

GM’s Recommended Solutions

The TSB outlines specific repair procedures to address these issues. This includes repairing the wiring using standard service manual procedures, ensuring proper connections, and checking for any loose grounds. GM has also provided detailed descriptions of the areas of concern for technicians to focus on during the repair process.

CAC pump electrical connector

An open cavity or an unsealed pump connector allowing water into the (M10) charge air cooler pump electrical connector might be the root cause of the communication failure. (Image Courtesy GM)
An open cavity or an unsealed pump connector allowing water into the (M10) charge air cooler pump electrical connector might be the root cause of the communication failure. (Image Courtesy GM)

An open cavity or an unsealed pump connector
allowing water into the (M10) charge air cooler pump
electrical connector might be the root cause of the
communication failure.

Check the CAC Pump connector sealing and look for
any corrosion at the pump due to water leakage.
DTCs that may be common with water intrusion the
electrical connector:

Note: U02A9 might be set with or without U1345 (LIN
BUS1 Failure).

• P0700 Transmission Control Module Requested
Malfunction Indicator Lamp Illumination
• P25A2 Brake System Control Module Requested
Malfunction Indicator Lamp Illumination
• U0284 Lost Communication with Active Grille Air
Shutter Actuator 1
• U0285 Lost Communication with Active Grille Air
Shutter Actuator 2
• U02A9 Lost Communication with Charge Air
Cooler Coolant Pump
• U0623 Lost Communication with Heater
Coolant Pump
• U0633 Lost Communication with Engine Cooling
Fan 2
• U1345 Engine Control Module LIN Bus 1
• U1600 Lost Communication with Transmission
Control Module on Engine Control Module LIN
Bus 1

Active grill shutter electrical harness

If the active shutter harness wires are not routed correctly, they may chafe (Image Courtesy GM)
If the active shutter harness wires are not routed correctly, they may chafe (Image Courtesy GM)

The following DTCs may be caused by the engine
wiring harness to active grille air shutter actuator in-line
connector (X618 on the pickup and X604A 0n the
SUV). Please check circuit 4621 which may be:
• Not properly connected
• Not properly held by the rear clip
• Grounded on the radiator

Check the active grill air shutter wiring route to
identify possible damaged points in the wiring.
DTCs that may be common with the wiring harness
contacting the radiator or an improper connection:

• P0700 Transmission Control Module Requested
Malfunction Indicator Lamp Illumination
• P25A2 Brake System Control Module Requested
Malfunction Indicator Lamp Illumination
• U0284 Lost Communication with Active Grille Air
Shutter Actuator 1
• U0285 Lost Communication with Active Grille Air
Shutter Actuator 2
• U02A9 Lost Communication with Charge Air
Cooler Coolant Pump
• U0623 Lost Communication with Heater
Coolant Pump
• U0632 Lost Communication with Cooling Fan
Motor
• U0633 Lost Communication with Engine Cooling
Fan 2
• U1345 Engine Control Module LIN Bus 1
• U1600 Lost Communication with Transmission
Control Module on Engine Control Module LIN
Bus 1

Engine wiring harness contacting the alternator bracket

A wire harness that has been compromised through contact with the alternator bracket (Image Courtesy GM)
A wire harness that has been compromised through contact with the alternator bracket (Image Courtesy GM)

For both the LM2 and the LZ0, the DTCs that may be
common with the wiring harness contacting the A/C
line and alternator bracket:

• P0700 Transmission Control Module Requested
Malfunction Indicator Lamp Illumination
• P10C6 Engine Diagnostic Status Signals
Message Counter Incorrect
• P1789 Current Transmission Range Unknown
• U0073 Control Module Communication CAN Bus
2 Off
• U0074 Control Module Communication CAN Bus
3 Off
• U0076 Control Module Communication Powertrain
Sensor CAN Bus Off
• U010E Lost Communication with Reductant
Control Module
• U0140 Lost Communication with Body Control
Module
• U0198 Lost Communication with Telematic
Control Module
• U029E Lost Communication with Nitrogen Oxides
Sensor 2
• U0402 Invalid Data Received from Transmission
Control Module
• U0403 Invalid Data Received from Transfer Case
Control Module
• U0404 Invalid Data Received from Gear Shift
Control Module
• U040F Invalid Data Received from Reductant
Control Module
• U0418 Invalid Data Received from Brake System
Control Module 1
• U0422 Invalid Data Received from Body Control
Module
• U1009 Reductant Control Module CAN Bus 3 Off
• U1345 Engine Control Module LIN Bus 1
• U1600 Lost Communication with Transmission
Control Module on Engine Control Module LIN
Bus 1
• U1609 Lost Communication with Serial Data
Gateway Module on CAN Bus 3
• U1610 Lost Communication with Brake System
Control Module 1 on CAN Bus 2
• U1643 Lost Communication with Transmission
Control Module on CAN Bus 2
• U18D2 Lost Communication with Gear Shift
Control Module on Powertrain Sensor CAN Bus
• U18D3 Lost Communication with Gear Shift
Control Module on CAN Bus 3
• U2204 Serial Data Gateway Module Lost
Communication with Reductant Control Module
• U220F Serial Data Gateway Module Lost
Communication with Transmission Control Module
• U2212 Reductant Control Module Lost
Communication with Engine Control Module
• U2405 Gear Shift Control Module Lost
Communication with Engine Control Module on
CAN Bus 2
• U2419 Serial Data Gateway Module Lost
Communication with Brake System Control
Module 1 on CAN Bus 2
• U241C Serial Data Gateway Module Lost
Communication with Engine Control Module on
CAN Bus 2
• U241D Serial Data Gateway Module Lost
Communication with Engine Control Module on
CAN Bus 3

Loose Ground Wire

Location of potential loose ground wires on the 3.0L Duramax Diesel Engine (Image Courtesy GM)
Location of potential loose ground wires on the 3.0L Duramax Diesel Engine (Image Courtesy GM)

Inspect ground connections G176A (1) and G177B (2)
may exist. Please check for any:

• Loosen condition
• Damaged or dirty threads

DTCs that may be common with a loose ground:
• P00EB Intake Air Temperature Sensor 3
Circuit High
• P0108 Manifold Absolute Pressure Sensor
Circuit High
• P045A Exhaust Gas Recirculation Valve 2 Control
Circuit
• P0494 Cooling Fan Speed Too Low — Left Side
• P0615 Starter Relay Control Circuit
• P0617 Starter Relay Control Circuit High Voltage
• P0628 Fuel Pump Control Circuit Low
• P0700 Transmission Control Module Requested
Malfunction Indicator Lamp Illumination
• P1098 Engine Coolant Control Valve Position
Sensor Minimum Stop Performance — Internal
Component Fault
• P129F Fuel Pump Power Control Module Fuel
Pump Speed Signal Incorrect
• P12A6 Fuel Pump Power Control Module Enable
Circuit Performance
• P189C Transmission Range Command Message
Performance
• P2053 Reductant Injector 2 Control Circuit
• P305D DC/DC Converter Crank Input Signal
Circuit High Voltage
• P3187 Fuel Pump Pressure Performance – Low
Pressure
• P31C3 Stop/Start System Performance
• U0284 Lost Communication with Active Grille Air
Shutter Actuator 1
• U0285 Lost Communication with Active Grille Air
Shutter Actuator 2
• U02A9 Lost Communication with Charge Air
Cooler Coolant Pump
• U0585 Invalid Data Received from Active Grille Air
Shutter Actuator 1
• U0586 Invalid Data Received from Active Grille Air
Shutter Actuator 2
• U0623 Lost Communication with Heater
Coolant Pump
• U0632 Lost Communication with Cooling Fan
Motor
• U0633 Lost Communication with Engine Cooling
Fan 2
• U0650 Lost Communication with Exhaust
Pressure Regulator Valve Position Sensor
• U1345 Engine Control Module LIN Bus 1
• U1346 Engine Control Module LIN Bus 2
• U1347 Engine Control Module LIN Bus 3
• U137E Invalid Data Received from Auxiliary
Coolant Pump
• U1600 Lost Communication with Transmission
Control Module on Engine Control Module LIN
Bus 1

What This Means for You

As a GM vehicle owner, being aware of these potential issues is crucial. While they might not affect every vehicle, knowing the signs can help you address any concerns proactively. If you notice any of these symptoms, you should visit your local GM dealership or a certified technician for a thorough inspection and potential repair.

If you think these issues may apply to you, please ask your dealership to reference TSB 23-NA-102