Skip to content
Tahoe / Yukon Service Manual

DTC P0128 or P01F0

Engine Controls and Fuel - 5.3L L84 or 6.2L L87 | Diagnostic Information and Procedures | Document ID: 5411652 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 P0128 Engine Coolant Temperature Below Thermostat Regulating Temperature DTC P01F0 Coolant Temperature Dropped Below Diagnostic Monitoring Temperature Diagnostic Fault Information

Circuit Short to Ground Open/High Resistance Short to Voltage Signal Performanc
Signal P0117, P0119 P0118, P0119 P0118, P0119 * P0116, P0119, P0128
Low Reference — P0118, P0119 ** * P0119, P0128
* Internal control module or component damage may occur if the circuit shorts to B+. ** Additional DTCs may set

Typical Scan Tool Data Engine Coolant Temperature Sensor

Circuit Short to Ground Open Short to Voltage
Operating Conditions: Engine = Idling — At normal operating temperature. Parameter Normal Range: 88 to 105°C (190 to 221°F)
Signal 150°C (302°F) −40°C (−40°F) −40°C (−40°F)
Low Reference — −40°C (−40°F) —

Circuit/System Description For an overview of the component/system, refer to: Cooling System Description and Operation

Circuit Description
Signal The control module input circuit has an internal resistance connected to 5 V.
Low Reference Grounded through the control module.
Component Description
B34 Engine Coolant Temperature Sensor The sensor is a negative temperature coefficient thermistor. As the temperature of the air, fluid, or metal increases, the resistance of the sensor decreases, varying the voltage on the signal circuit.
K20 Engine Control Module The control module contains a microprocessor used to process input data to control outputs. The control module controls a series of actuators to ensure optimal engine performance. The control module does this by reading values from a variety of sensors, interprets the data and adjusts the engine actuators accordingly.

The engine control module (ECM) monitors the temperature of the engine coolant for engine control and as an enabling criteria for some diagnostics. The amount of heat an engine generates is proportional to the amount of air that enters the engine. The ECM monitors this amount of air to calculate a theoretical engine coolant temperature (ECT). The ECM uses the calculated temperature to determine the following: { P0128 } The measured engine coolant temperature fails to reach the regulated temperature, before a predetermined amount of air has entered the engine. { P01F0 } The engine coolant temperature reaches the regulated temperature and then falls below a predetermined value for a calibrated amount of time. Conditions for Running the DTC P0128 DTCs related to the following system/component = Not Set – B34 Engine Coolant Temperature Sensor – B66 Intake Air Temperature Sensor – B75 Mass Air Flow Sensor – B115 Vehicle Speed Sensor – G17 Heater Coolant Pump Engine Coolant Thermostat Heater Command = Less than 20% — For greater than 5 s Engine Off Time = Greater than 30 min Engine Run Time = 30 s to 25 min Start-Up Engine Coolant Temperature Sensor = −40 to 52°C (−40 to 125°F) Vehicle Distance Traveled During Drive Cycle = Greater than 1.2 km (.8 mi) Frequency the DTC runs = Once — Per ignition cycle — After the running conditions are met P01F0 DTC P0116, P0117, P0118, P0119 = Not set Ambient Air Temperature = Greater than −9°C (21°F) Barometric Pressure = Greater than 55 kPa (8 PSI) Cylinder Deactivation System = Inactive Deceleration Fuel Cut-Off = Active — For less than 23 s Engine Coolant Temperature Sensor = Greater than 75°C (167°F) — At least 1 time(s) during the ignition cycle Engine Run Time = Greater than 1 s Engine Speed = Less than 3,800 RPM Vehicle Distance Traveled During Drive Cycle = Greater than 1.2 km (.8 mi) Conditions for Setting the DTC P0128 Engine Coolant Temperature = Not within a calibrated range P01F0 Engine Coolant Temperature = Less than 65°C (149°F) — For greater than 60 s Actions Taken When the DTC Sets DTCs listed in the DTC Descriptor category = Type B DTC Cooling Fan = On Conditions for Clearing the DTC DTCs listed in the DTC Descriptor category = Type B DTC Diagnostic Aids { P0128 } The parameters for intake air temperature and engine coolant temperature should be within 3°C (5°F) of each other if the ignition has been Off for greater than 8 h. High resistance in the circuits of the component may set DTC P0128, P01F0 without setting the DTC for the component: B34 Engine Coolant Temperature Sensor Reference Information Schematic Reference Engine Controls Schematics Connector End View Reference Master Electrical Component List 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 Circuit/System Verification

  1. Verify the condition does not exist: Incorrect fluid level or condition » Refer to: Loss of Coolant ⇒ If a condition exists Repair or replace as necessary ⇓ If no condition exists
  2. Verify there are no DTCs set related to the following component/system: B34 Engine Coolant Temperature Sensor ⇒ If a related DTC is set Refer to: Diagnostic Trouble Code (DTC) List - Vehicle ⇓ If a related DTC is not set
  3. Engine » Running @ 1,800 to 2,200 RPM Verify the scan tool parameter: Engine Coolant Temperature Sensor = Greater than 80°C (176°F) — Within 15 min ⇒ If 80°C (176°F) or colder Test or replace the component: Engine Coolant Thermostat ⇓ If warmer than 80°C (176°F)
  4. All OK. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair: Diagnostic Repair Verification Water Pump Inlet Replacement For control module replacement, programming, and setup refer to: Control Module References