PRE-RELEASE
DTC P0128 (LF1, LFW)
| DTC P0128 (LF1, LFW) |
| Diagnostic Instructions |
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Perform the
Diagnostic System Check - Vehicle
prior to using this diagnostic procedure.
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Review
Strategy Based Diagnosis
for an overview of the diagnostic approach.
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Diagnostic Procedure Instructions
provides an overview of each diagnostic category.
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| 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 |
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Before the ECM can report DTC P0128 failed, DTC P0117 and P0118 must run and pass.
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DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0114, P0116, P0117, P0118, P0121, P0122, P0123, P0502, or P0503 is not set.
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The Engine has not run for greater than 30 minutes.
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The Engine run time from a cold start is greater than 2 minutes.
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The ECT is colder than 50°C (122°F) at start up.
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The vehicle speed is greater than 8 km/h (5 mph) for more than 2.4 km/h (1.5 miles) .
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The Ethanol content of the fuel is less than 87 percent.
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DTC P0128 runs continuously once the above conditions have been met for approximately 15 min.
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DTCs P0116, P0117, or P0118 is not set.
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The block heater is not detected.
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DTC P0128 runs continuously once the above conditions have been met for approximately 8 min.
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| Conditions for Setting the DTC |
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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.
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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.
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| Action Taken When the DTC Sets |
DTC P0128 is a Type B DTC.
| Conditions for Clearing the MIL/DTC |
DTC P0128 is a Type B DTC.
| 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
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Circuit Testing
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Connector Repairs
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Testing for Intermittent Conditions and Poor Connections
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Wiring Repairs
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DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
| Circuit/System Verification |
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Verify that the engine coolant level is correct.
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| 2. |
If the engine coolant is not at the correct level, refer to
Loss of Coolant
.
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| 3. |
Verify that the engine coolant temperature is at the normal operating temperature.
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If the engine coolant temperature is colder than the normal operating temperature, refer to
Thermostat Diagnosis
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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.
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| Circuit/System Testing |
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Ignition OFF, disconnect the harness connector at the B34 ECT sensor.
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Test for less than 5 Ω between the low reference circuit terminal 2 and ground. |
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Warning
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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.
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With the ignition ON, check the scan tool's parameter for the ECT sensor. Check that the ECT sensor parameter is 40 °C (-40 °F).
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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.
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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). |
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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.
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If all circuits test normal, test or replace the B34 ECT sensor.
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| Component Testing |
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Ignition OFF, disconnect the harness connector at the B34 ECT sensor.
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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. |
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If not within the specified range, replace the B34 ECT sensor.
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| Repair Instructions |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
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Engine Coolant Temperature Sensor Replacement (LAU)
Engine Coolant Temperature Sensor Replacement (LF1)
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Control Module References
for ECM replacement, setup, and programming
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