Circuit Description
While the engine is warming, the powertrain control module (PCM) monitors the engine coolant temperature (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 diagnostic trouble code (DTC) on a cold start and only once per cold start.
Conditions for Running the DTC
| • | The PCM performs this DTC diagnostic once per ignition cycle until a pass or fail condition exists. |
| • | The engine operation time is more than 600 seconds. |
| • | DTCs P0112, P0113, P0117, or P0118 are not set. |
| • | The intake air temperature (IAT) is more than -7°C (20°F). |
| • | The total idle time since start up is less than 450 seconds. |
or
| • | The engine operation time is more than 300 seconds. |
| • | DTCs P0112, P0113, P0117, or 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 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. |
Diagnostic Aids
| Important: The system must be rechecked on a cold start. |
| • | Using Freeze Frame/Failure Records data may aid in locating an intermittent condition. If the DTC cannot be duplicated, the information included in the Freeze Frame/Failure Records data can be useful in determining how many kilometers (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-volt reference circuit, check for faulty connections and for faulty wiring. |
| • | If the engine 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 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 Testing for Electrical Intermittents in Wiring Systems.
If a repair is necessary, then refer to Wiring Repairs or Connector Repairs in Wiring Systems.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
An ECT failure could cause a DTC P0126 to set, so correct any ECT DTCs that are set.
-
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.
Step | Action | Values | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||
Are any engine coolant temperature DTCs set? | -- | Go to Step 3 | ||||||||||
3 |
Does the scan tool indicate the ECT sensor is below a temperature colder than the specified value? | -35°C (-31°F) | Go to Step 4 | Go to DTC P0117 | ||||||||
4 | Using a jumper wire, jumper terminals at the ECT sensor harness connector together. Does the scan tool indicate the ECT is at a temperature greater than the specified value? | 150°C (302°F) | Go to Step 5 | Go to DTC P0118 | ||||||||
5 |
Important: Allow time for the engine to warm up if the engine has not already reached the specified temperature. Seven minutes is the maximum amount of time the engine should take to reach this temperature from a cold start. Less time should be necessary if the engine is already warm. Does the scan tool indicate the engine coolant temperature has reached the specified value? | 60°C (140°F) | Go to Diagnostic Aids | Go to Step 6 | ||||||||
Using a DMM, measure the resistance of the ECT sensor. Does the ECT resistance measure near the value indicated in the Temperature Vs Resistance Table? | -- | Go to Step 7 | Go to Step 8 | |||||||||
7 | For an engine cooling system problem, check for the following conditions:
Refer to Symptoms - Engine Cooling Engine Cooling. Did you complete the repair? | -- | Go to Step 9 | -- | ||||||||
8 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 9 | -- | ||||||||
9 |
Does the DTC run and pass? | -- | Go to Step 10 | Go to Step 2 | ||||||||
10 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||||
