GM/Detroit 6.5L ENGINE CONTROLS – DTC P0126 Engine Coolant Temperature (ECT) Insufficient for Stable Operation

Circuit Description
While the engine is warming, the PCM monitors the ECT sensor to determine how long it takes the engine to reach the coolant temperature required for Closed Loop operation. DTC P0126 will set if the PCM determines that the engine does not reach Closed Loop temperature in a specified amount of time. This test will not run if either the intake air or engine coolant temperature is too low at start up. The PCM will only run this DTC on a cold start and only once per cold start.

Conditions for Running the DTC
• The PCM performs this DTC diagnostic once perignition cycle until a pass or fail condition exists.
• The engine operation time is more than 600 seconds.

• The DTCs P0112, P0113, P0117 and P0118 are not set.
• The intake air temperature is more than -7°C (20°F).
• The total idle time since start up is less than 450 seconds.
• The engine operation time is more than 300 seconds.
• The DTCs P0112, P0113, P0117 and P0118 are not set.
• The intake air temperature is more than -7°C (20° F).

Conditions for Setting the DTC
• The fuel burned since start up is more than 1,000,000 cu. mm.
• The engine coolant is less than 56°C (133°F).
or
• The fuel burned since start up is more than 468,120 cu. mm.
• The engine coolant temperature is less than 56°C (133°F).

Action Taken When the DTC Sets
• The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive drive trip that the diagnostic runs and fails.
• The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the Failure Records will store this information. If the diagnostic reports a failure on the second consecutive drive trip, the Freeze Frame records the operating conditions at the time of failure and updates the Failure Records.

Conditions for Clearing the MIL/DTC
• The PCM will turn the MIL off after three consecutive trips without a fault condition.
• A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures
• The use of a scan tool.

Diagnostic Aids
Important: The system must be rechecked on a cold start.
• Using Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If the DTC cannot be duplicated, the information included in the Freeze Frame and/or Failure Records data can be useful in determining how many miles since the DTC set. The Fail Counter and Pass Counter can also be used to determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that were noted. This will isolate when the DTC failed.
• If other DTCs are set that share the same ground and/or 5.0 volt reference circuit, check for faulty connections and for faulty wiring.

• If the engjne has been allowed to sit overnight, the engine coolant temperature and intake air temperature values should display within a few degrees of each other.
• If the engine coolant temperature exceeds 60°C (140°F), this indicates that the engine is capable of reaching the proper temperature, but not necessarily in the correct amount of time. This diagnostic table must be repeated on a cold engine, ECT and IAT less than 50°C (122°F) and within 3°C (5°F) of each other, and the time required to reach the temperature threshold must be measured. When starting a cold engine, measure the amount of time it takes the engine to reach the specified temperature. The engine should reach the specified temperature within 8 minutes. If the specified temperature is not reached within 7 minutes, check the following:
• Coolant level.
• Thermostat operation.
• Cooling fan.
• Refer to Thermostat Diagnosis (On-Vehicle) in Engine Cooling for additional information.

An intermittent may be caused by any of the following conditions:
• A poor connection
• Rubbed through wire insulation
• A broken wire inside the insulation

Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.
If a repair is necessary, then refer to Wiring Repairs or Connector Repairs in Wiring Systems.

Test Description
Number(s) below refer to step numbers on the diagnostic table.
2. An ECT failure could cause a DTC P0126 to set, so correct any ECT DTCs that are set.
6. If it is obvious that the engine is not reaching full operating temperature, for example the radiator hoses never gets very warm, or there is a complaint of little or no heat from the heater, this step could be skipped.

 

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