DTC P0126

DTC P0126	Insufficient coolant temperature for stable operation
DETECTION CONDITION	The PCM monitors the ECT after the engine start for a certain period. If the ECT never exceeds 71°C {160°F} when the following conditions are met, the PCM determines that the coolant thermostat is stuck open. MONITORING CONDITIONS ECT at engine start: less than 51°C {123°F} Estimated ambient temperature: more than -10°C {14°F} Diagnostic support note This is a continuous monitor (thermostat). The MIL illuminates if the PCM detects the above malfunction condition in two consecutive drive cycles or in one drive cycle while the DTC for the same malfunction has been stored in the PCM. PENDING CODE is available if the PCM detects the above malfunction condition during the first drive cycle. FREEZE FRAME DATA (Mode 2/Mode 12) is available. The DTC is stored in the PCM memory.
POSSIBLE CAUSE	VSS malfunction IAT sensor malfunction ECT sensor malfunction Coolant thermostat malfunction PCM malfunction

Insufficient coolant temperature for stable operation

DETECTION CONDITION

The PCM monitors the ECT after the engine start for a certain period. If the ECT never exceeds 71°C {160°F} when the following conditions are met, the PCM determines that the coolant thermostat is stuck open.

MONITORING CONDITIONS

ECT at engine start: less than 51°C {123°F}
Estimated ambient temperature: more than -10°C {14°F}

Diagnostic support note

This is a continuous monitor (thermostat).
The MIL illuminates if the PCM detects the above malfunction condition in two consecutive drive cycles or in one drive cycle while the DTC for the same malfunction has been stored in the PCM.
PENDING CODE is available if the PCM detects the above malfunction condition during the first drive cycle.
FREEZE FRAME DATA (Mode 2/Mode 12) is available.
The DTC is stored in the PCM memory.

POSSIBLE CAUSE

VSS malfunction
IAT sensor malfunction
ECT sensor malfunction
Coolant thermostat malfunction
PCM malfunction

DIAGNOSTIC PROCEDURE

STEP	INSPECTION		ACTION
1	VERIFY FREEZE FRAME DATA (MODE 12) AND DIAGNOSTIC MONITORING TEST RESULTS HAVE BEEN RECORDED Have the FREEZE FRAME DATA (Mode 12) and DIAGNOSTIC MONITORING TEST RESULTS (thermostat related) been recorded?	Yes	Go to the next step.
1		No	Record the FREEZE FRAME DATA (Mode 12) and DIAGNOSTIC MONITORING TEST RESULTS on the repair order, then go to the next step.
2	VERIFY RELATED REPAIR INFORMATION AVAILABILITY Verify related Service Bulletins and/or on-line repair information availability. Is any related repair information available?	Yes	Perform repair or diagnosis according to the available repair information. If the vehicle is not repaired, go to the next step.
2		No	Go to the next step.
3	VERIFY FOR OTHER STORED DTC Turn the ignition switch off, then to the ON position (engine off). Verify for the other stored DTCs. Are other DTCs present?	Yes	Go to the appropriate DTC inspection. (See DTC TABLE ).
3		No	Go to the next step.
4	VERIFY CURRENT INPUT SIGNAL STATUS OF VSS Start the engine. Access the VSS PID using the M-MDS. (See ON-BOARD DIAGNOSTIC TEST ). Inspect the VSS PID. Is the PID normal? (See PCM INSPECTION ).	Yes	Go to the next step.
4		No	Repair or replace the malfunctioning part according to the inspection results, then go to Step 9.
5	INSPECT IAT SENSOR Inspect the IAT sensor. (See INTAKE AIR TEMPERATURE (IAT) SENSOR INSPECTION ). Is there any malfunction?	Yes	Replace the MAF/IAT sensor, then go to Step 9. (See MASS AIR FLOW (MAF)/INTAKE AIR TEMPERATURE (IAT) SENSOR REMOVAL/INSTALLATION ).
5		No	Go to the next step.
6	INSPECT ECT SENSOR Inspect the ECT sensor. (See ENGINE COOLANT TEMPERATURE (ECT) SENSOR INSPECTION ). Is there any malfunction?	Yes	Replace the ECT sensor, then go to Step 9. (See ENGINE COOLANT TEMPERATURE (ECT) SENSOR REMOVAL/INSTALLATION ).
6		No	Go to the next step.
7	INSPECT COOLANT THERMOSTAT Inspect the coolant thermostat. (See THERMOSTAT INSPECTION ). Is there any malfunction?	Yes	Replace the coolant thermostat, then go to Step 9. (See THERMOSTAT REMOVAL/INSTALLATION ).
7		No	Go to the next step.
8	VERIFY MONITORING CONDITION FOR REPAIR VERIFICATION Leave the vehicle in a place that is at a temperature of approx. 25°C {77°F} for more than 6 hours. Make sure to reconnect all disconnected connectors. Clear the DTC from the PCM memory using the M-MDS. (See AFTER REPAIR PROCEDURE ). Access the ECT and IAT PIDs using the M-MDS. Verify that each PID is within following specifications. IAT: more than -10°C {14°F} ECT: less than 51°C {123°F} Are the ECT and IAT PIDs normal?	Yes	Go to the next step.
8		No	Repair or replace the malfunctioning part according to the inspection results, then repeat this step.
9	VERIFY TROUBLESHOOTING OF DTC P0126 COMPLETED Start the engine and turn off E/L and A/C. Access and monitor PIDs TH_M (temp unit) and TH_M_MIN (temp unit) using the M-MDS. NOTE: This test requires actual driving. Chassis roller cannot be used for this test. During the test drive, constant speed should be maintained, although 2 or 3 stops during every 5 min of driving time (e.g. for traffic signals) is acceptable. Stop-and-go (e.g. in case of traffic congestion) is not acceptable during the test period. Test period depends on ECT at the engine start, (e.g. if ECT is -10°C {14°F}, monitoring period is 38 min and ECT is 30°C {86°F}, monitoring period is 8 min) Verify the PIDs TH_M and TH_M_MIN values. Is the TH_M value above TH_M_MIN value?	Yes	Go to the next step.
9		No	Replace the PCM, then go to the next step. (See PCM REMOVAL/INSTALLATION ).
10	VERIFY AFTER REPAIR PROCEDURE Perform the "AFTER REPAIR PROCEDURE ". (See AFTER REPAIR PROCEDURE ). Are any DTCs present?	Yes	Go to the applicable DTC inspection. (See DTC TABLE ).
10		No	DTC troubleshooting completed.