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. This is a type B DTC.
Conditions for Setting the DTC
| • | Engine run time greater than 600 seconds. |
| • | DTCs P0112, P0113, P0117, P0118, not set. |
| • | Engine coolant less than 56°C (133°F). |
| • | Intake air greater than -7°C (20°F). |
| • | Fuel burned since start is greater than 1,000,000 cu. mm. |
| • | Total idle time since start is less than 450 seconds. |
or
- Engine run time greater than 300 seconds.
- DTCs P0112, P0113, P0117, P0118, not set.
- Engine coolant less than 56°C (133°F).
- Intake air greater than -7°C (20°F).
- Fuel burned since start is greater than 468,120 cu. mm.
- Total idle time since start is less than 225 seconds.
Action Taken When the DTC Sets
| • | The PCM will illuminate the Malfunction Indicator Lamp (MIL) on the second consecutive drive trip that the diagnostic runs and fails. |
| • | The PCM will record operating conditions at the time the diagnostic fails. The first time the diagnostic fails, this information will be stored in Failure Records. If the diagnostic reports a failure on the second consecutive drive trip, the operating conditions at the time of failure will be written to Freeze Frame and the Failure record will be updated. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail. |
| • | A last test failed (Current DTC) will clear when the ignition is cycled and the diagnostic runs and does not fail. |
| • | A History DTC will clear after forty consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | PCM battery voltage is interrupted. |
| • | Using a Scan tool. |
Diagnostic Aids
| • | 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 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 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, engine coolant and intake air temperature 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 Engine Cooling System (6B) for additional information. |
Test Description
Number(s) 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 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 | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||||||||||
Are any engine coolant temperature DTCs set? | -- | Go to applicable DTC table | ||||||||||
3 |
Does scan tool indicate the ECT sensor is less than the specified value? | -35°C (-31°F) | Go to DTC P0117 Engine Coolant Temperature (ECT) Sensor Circuit Low Voltage | |||||||||
4 | Using a jumper wire, jumper terminals at the ECT sensor harness connector together. Does the scan tool indicate the ECT is greater than the specified value? | 150°C (302°F) | Go to DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit High Voltage | |||||||||
5 |
Important: Allow time for the engine to warm up if it has not already reached the specified temperature. 7 minutes is the maximum amount of time it 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 reached the specified value? | 60°C (140°F) | System must be rechecked on a cold start. Refer to Diagnostic Aids | |||||||||
Using a DVM (J 39200), measure the resistance of the ECT sensor. Refer to Temperature vs Resistance Is the ECT resistance close to the value indicated in the Temperature Vs Resistance Table? | -- | |||||||||||
7 | For an engine cooling system problem, check for the following conditions:
Refer to Engine Cooling System. Is the action complete? | -- | -- | |||||||||
8 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement Is the action complete? | -- | -- | |||||||||
9 |
Does the scan tool indicate that this test passed? | -- | ||||||||||
10 | Using the scan tool, select Capture Info, Review Info. Are any DTCs displayed that have not been diagnosed? | -- | Go to the applicable DTC table | System OK |
