Circuit Description
While the engine is warming, the powertrain control module (PCM) monitors the engine coolant temperature (ECT) sensor to determine how long the engine takes to reach the coolant temperature that is 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 the 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 test 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 engine coolant temperature (ECT) is less than 56°C (133°F). |
| • | The intake air temperature (IAT) is more than -7°C (20°F). |
or
| • | The engine operation time is more than 300 seconds. |
| • | DTCs P0112, P0113, P0117, or P0118 are not set. |
| • | The engine coolant temperature (ECT) is less than 56°C (133°F). |
| • | The intake air temperature (IAT) 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 total idle time since start-up is less than 450 seconds. |
or
| • | The fuel burned since start-up is more than 468,120 cu. mm. |
| • | The total idle time since start-up is less than 225 seconds. |
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 the Freeze Frame/Failure Records data may aid in locating an intermittent condition. If the DTC cannot be duplicated, the Freeze Frame/Failure Records data can be used to determine how many miles were driven since the DTC set. The Fail Counter and Pass Counter can also be used to determine how many ignition cycles the diagnostic test reported a pass and/or a fail. Operate the vehicle within the same Freeze Frame conditions that existed when the condition was noted. These conditions may include RPM, load, vehicle speed, temperature, or others. This procedure will help to 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 the 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, with the engine coolant temperature and the intake air temperature less than 50°C (122°F) and within 3°C (5°F) of each other. The time required to reach the temperature threshold must be measured. When starting a cold engine, measure the amount of time the engine takes 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 items: |
| • | The coolant level |
| • | The thermostat operation |
| • | The cooling fan |
Test Description
The numbers below refer to 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 the engine is not reaching full operating temperature, for example the radiator hoses never get 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 that the ECT sensor is at a temperature that is colder than the specified value? | -35°C (-31°F) | Go to Step 4 | Go to DTC P0117 | ||||||||
4 | Using a jumper wire, jumper the terminals at the ECT sensor harness connector together. Does the scan tool indicate the ECT is at a temperature that is more 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 that the engine coolant temperature has reached the specified value? | 60°C (140°F) | Go to Diagnostic Aids | Go to Step 6 | ||||||||
Use a DMM in order to measure the resistance of the ECT sensor. Refer to Temperature Versus Resistance . Is the ECT resistance close to the value that is indicated in the Temperature Vs Resistance table? | -- | Go to Step 7 | Go to Step 8 | |||||||||
7 | For an engine cooling system condition, check for the following conditions:
Did you find and correct the condition? | -- | 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 scan tool indicate the diagnostic passed? | -- | Go to Step 10 | Go to Step 2 | ||||||||
10 | Does the scan tool display any additional undiagnosed DTCs? | -- | System OK | |||||||||
