P0128
The content of this article/image reflects the changes identified in
TSB #06-06-04-024
and applies to 2006 Cadillac DTS
DTC P0128
DTC DESCRIPTOR
DTC P0128
Engine Coolant Temperature (ECT) Below Thermostat Regulating Temperature
DIAGNOSTIC FAULT INFORMATION
IMPORTANT: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Testing and Inspection
TYPICAL SCAN TOOL DATA
ECT Sensor Temperature:
CIRCUIT/SYSTEM DESCRIPTION
The engine coolant temperature (ECT) sensor is a variable resistor that measures the temperature of the engine coolant. The engine control module (ECM) supplies 5 volts to the ECT signal circuit and supplies a ground to the low reference circuit.
The purpose of this rationality diagnostic is to determine if the engine coolant will heat up at the correct rate, and also meet the calibrated target temperatures under various operating conditions.
The ECM uses the start-up ECT, and the start-up intake air temperature (IAT) to begin the diagnostic calculation. The air flow into the engine is accumulated, and vehicle speed, distance and engine run time are also factored in, to determine if the ECT does increase normally, and reach the calibrated target temperatures.
CONDITIONS FOR RUNNING THE DTC
- DTCs P0101, P0102, P0103, P0112, P0113, P0116, P0117, P0118, P0502, P0503 are not set.
- The start-up IAT is more than -7°C (20°F).
- The start-up ECT is less than 80°C (176°F).
- The engine run time is between 60-1,370 seconds.
- The vehicle has traveled more than 0.8 kilometers (0.5 miles) at more than 8 km/h (5 mph).
- The mass air flow (MAF) is between 10-35 g/s.
- This DTC runs once per ignition cycle within the enabling conditions.
CONDITIONS FOR SETTING THE DTC
The ECM detects that the minimum ECT of 80°C (176°F) has not been met.
ACTION TAKEN WHEN THE DTC SETS
- The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
- The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.
CONDITIONS FOR CLEARING THE MIL/DTC
- The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
- A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
- A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
- Clear the MIL and the DTC with a scan tool.
CIRCUIT/SYSTEM VERIFICATION
1. If the ignition has been OFF for 8 hours or more, the ECT and the IAT, should be within 6°C (11°F) of each other and also the ambient temperature. Turn ON the ignition, with the engine OFF, and use a scan tool to observe the IAT and the ECT sensor parameters.
2. Inspect the ECT sensor terminals for corrosion, and for engine coolant leaking through the sensor.
3. Use the scan tool to verify the proper operation of the engine cooling system fans.
4. Turn OFF the ignition.
CAUTION: Under pressure, the temperature of the solution in the radiator can be considerably higher, without boiling. Removing the radiator cap while the engine is hot (pressure is high), will cause the solution to boil instantaneously, with explosive force. The solution will spew out over the engine, fenders, and the person removing the cap. Serious bodily injury may result. Flammable antifreeze, such as alcohol, is not recommended for use at any time. Flammable antifreeze could cause a serious fire.
5. Inspect the cooling system surge tank for the proper engine coolant level. Refer to Cooling System Leak Testing and Draining and Filling Cooling System (Static Fill) Draining and Filling Cooling System (Vac-N-Fill). Component Tests and General Diagnostics Service and Repair
6. Verify the proper heat range, and the operation of the thermostat. Refer to Thermostat Diagnosis. Symptom Related Diagnostic Procedures
IMPORTANT: A critical analysis of the operation of the thermostat is necessary, to properly diagnose these DTCs.
CIRCUIT/SYSTEM TESTING
IMPORTANT:
All electrical components and accessories must be turned off and allowed to power down.
1. Ignition OFF, disconnect ECT harness connector at the ECT sensor.
2. Ignition OFF, test for less than 5ohms of resistance between the low referance circuit terminal B and ground.
- If greater than the specified range, test the low referance circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
- Ignition On, verify the scan tool ECT sensor paramiter is less than -39°c(-38°f).
- If greater than the specified range, test the signal circuit terminal A for a short to ground. If the circuit test normal replace the ECM.
- Install a 3-amp fused jumper wire between the signal circuit terminal A and the low referance circuit terminal B. Verify the scan tool ECT sensor paramiter is greater than 149°c(300°f)
- If less than the specified range,test the signal circuit for a short to voltage or and open/high resistance . If the circuit test normal replace the ECM.
- If all circuits test normal, test or replace the ECT sensor
COMPONENT TESTING
Measure and record the resistance of the ECT sensor at various ambient temperatures, and then compare those measurements to the Temperature vs Resistance Table. Refer to Temperature vs Resistance.
REPAIR INSTRUCTIONS
IMPORTANT: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure.
- Engine Coolant Temperature (ECT) Sensor Replacement
- Control Module References for ECM replacement, setup, and programming Verification Tests