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DTC P0128 (LAU)

DTC P0128 (LAU)

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 Descriptor

DTC P0128

Engine Coolant Temperature (ECT) Below Thermostat Regulating Temperature

Circuit Description

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 air flow into an engine is proportional to the amount of heat an engine generates. The ECM monitors the amount of air flow into the engine to calculate engine coolant temperature (ECT). The ECM uses the calculated temperature to determine if the engine has warmed up to the closed loop temperature or to the thermostat regulating temperature. If the coolant temperature does not increase normally or does not reach the closed loop temperature, diagnostics that use the ECT as enabling criteria, may not run when expected.

Conditions for Running the DTC


P0128

• Before the ECM can report DTC P0128 failed, DTC P0117 and P0118 must run and pass.

• DTCs P0100, P0101, P0102, P0103, P0111, P0112, P0113, P0116, P0117, P0118, P0119, or P0700 is not set.

• The engine speed is greater than 960 RPM.

• The ECT is colder than 51°C (124°F) at start up.

• The vehicle speed is greater than 8 km/h (5 mph).

• The air flow coming into the engine has accumulated to greater than 3,459 grams.

• DTC P0128 runs continuously once the above conditions have been met for approximately 15 min.

OR

• DTCs P0116, P0117, P0118, or P0119 is not set.

• The engine speed is greater than 25 RPM.

• The block heater is not detected.

• DTC P0128 runs continuously once the above conditions have been met for approximately 8 min.


Conditions for Setting the DTC


P0128

• The ECM detects that the actual engine coolant temperature is 11°C (20°F) colder than the calculated thermostat regulating temperature of 89°C (192°F), for greater than 4 s or for a cumulative of 30 s.

OR

• The ECM detects that the actual engine coolant temperature is 10°C (18°F) colder than the calculated ECT for greater than 1 s or a cumulative of 10 s.


Action Taken When the DTC Sets

DTC P0128 is a Type B DTCs.

Conditions for Clearing the MIL/DTC

DTC P0128 is a Type B DTCs.

Diagnostic Aids

An engine that soaks for about 8 h will help diagnosis the condition. After the cold soak, operate the vehicle at highway speeds for 20 min while monitoring the scan tool Calculated ECT - Thermostat parameter. If there is a condition, the calculated temperature will be 10°C (18°F) warmer than the actual engine coolant temperature.

Reference Information

Schematic Reference

Engine Controls Schematics (3.0L (LF1)) Engine Controls Schematics (2.8L (LAU))

Connector End View Reference

Component Connector End Views

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. Verify that the engine coolant level is correct.

2. If the engine coolant is not at the correct level, refer to Loss of Coolant .

3. Verify that the engine coolant temperature is at the normal operating temperature.

4. If the engine coolant temperature is colder than the normal operating temperature, refer to Thermostat Diagnosis .

5. 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


1. Ignition OFF, disconnect the harness connector at the B34 ECT sensor.

2.
Warning

Do NOT use a test lamp to test the continuity of the circuit. Damage to the control module may occur due to excessive current draw.


Note

The control module or the sensor may be damaged if the circuit is shorted to battery positive voltage.


Test for less than 5 Ω between the low reference circuit terminal 2 and ground.

3. If greater than specified value, test the circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K20 ECM.

4. Ignition ON, observe the scan tool the ECT sensor parameter. Verify that the ECT sensor parameter is at -40 °C (-40 °F).

5. If warmer than the specified value, test the signal circuit for a short to ground. If the circuit/connections test normal, replace the K20 ECM.

6.
Note

If the fuse in the jumper wire opens, the signal circuit is shorted to a voltage and the ECT sensor may be damaged.


Install a 3 A fused jumper wire between the signal circuit terminal 1 and the low reference circuit terminal 2. Verify the scan tool ECT sensor parameter is warmer than 142°C (288°F).

7. If colder than the specified value, test the signal circuit for an open/high resistance or for a short to voltage. If the circuit/connections test normal, replace the K20 ECM.

8. If all circuits test normal, test or replace the B34 ECT sensor.


Component Testing


1. Ignition OFF, disconnect the harness connector at the B34 ECT sensor.

2.
Note

A thermometer can be used to test the sensor off the vehicle.


Test the ECT sensor by varying the sensor temperature while monitoring the sensor resistance. Compare the readings with the Temperature Versus Resistance - Engine Coolant Temperature Sensor table and verify that the resistance is within 5 % of the specification.

3. If not within the specified range, replace the B34 ECT sensor.


Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.


• Engine Coolant Temperature Sensor Replacement (LAU) Engine Coolant Temperature Sensor Replacement (LF1)

• Control Module References for ECM replacement, setup, and programming