DTC P18A8

Automatic Transmission - 10L80 MHS MQC | Diagnostic Information and Procedures | Document ID: 5337110 Diagnostic Instructions Perform the Diagnostic System Check prior to using this diagnostic procedure: Diagnostic System Check - Vehicle Review the description of Strategy Based Diagnosis: Strategy Based Diagnosis An overview of each diagnostic category can be found here: Diagnostic Procedure Instructions DTC Descriptor DTC P18A8 Transmission Park Control Solenoid Actuator Stuck On Diagnostic Fault Information

Note

DTC P18A8 will set with a hydraulic/mechanical condition. The components are listed from the least to the most intrusive to service.

Component	DTC	Condition
M123 Transmission Park Valve Lock Solenoid Actuator	P18A8	Binding or Sticking / Stuck
Control Valve Body Control Valve Body Spacer Plate Park Servo Valve / Spring	P18A8	Oil Channels or Orifices — Blocked by debris / Restricted Valve — Binding or Sticking / Stuck

Circuit/System Description For an overview of the component/system, refer to: Park - Engine Running Reverse Neutral - Engine Running Drive Range, First Gear Drive Range, Second Gear Drive Range, Third Gear Drive Range, Fourth Gear Drive Range, Fifth Gear Drive Range, Sixth Gear Drive Range, Seventh Gear Drive Range, Eighth Gear Drive Range, Ninth Gear Drive Range, Tenth Gear Electronic Component Description The Park Servo Valve is held out of park by fluid pressure or the M123 Transmission Park Valve Lock Solenoid Actuator . In neutral, there is not enough fluid pressure to hold the park servo valve out of park. The park servo valve is held out of the park position when the pin on the M123 is extended, holding the park servo valve. If the B316 Transmission Park Valve Position Switch detects the park position when in neutral, DTC P18A8 will set. Conditions for Running the DTC DTC P187D, P187E, P18A3, P18A4, P18AA, P18AB, P27EC = Not set DTCs related to the following system/component = Not Set – B315A Transmission Range Control Valve 1 Position Switch – B316 Transmission Park Valve Position Switch G5 Automatic Transmission Auxiliary Fluid Pump = Not Activated High Side Driver 1, 2 = On Battery Voltage = Greater than 9 V Engine = Running Ignition and Start Signal = 9 to 32 V Ignition and Start Switch Signal = On Transmission Range = N Frequency the DTC runs = Continuously — After the running conditions are met Conditions for Setting the DTC Transmission Range Command ≠ Actual — Transmission Range Control Valve 1 Position Switch Actions Taken When the DTC Sets DTCs listed in the DTC Descriptor category = Type B DTC Conditions for Clearing the DTC DTCs listed in the DTC Descriptor category = Type B DTC Reference Information DTC Type Reference Powertrain Diagnostic Trouble Code (DTC) Type Definitions Scan Tool Reference Control Module References Circuit/System Verification

1. Verify the condition does not exist: Incorrect fluid level or condition » Refer to: Transmission Fluid Level and Condition Check ⇒ If a condition exists Repair or replace as necessary ⇓ If no condition exists
2. Ignition » On / Vehicle » In Service Mode
3. Clear the DTCs.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data. Refer to: Road Test Verify that no DTC listed in the DTC Descriptor Category is set. ⇒ If any of the DTCs are set Refer to: Diagnostic Fault Information & Verify the conditions listed in the table do not exist ⇓ If none of the DTCs are set
5. All OK. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair: Diagnostic Repair Verification Control Valve Body Replacement For control module replacement, programming, and setup refer to: Control Module References