My "service engine soon" light is on. The OBD Code is P0125 which is "Closed Loop Fuel Control Insufficient Coolant temp"

I cleared the light once and it came back in a couple days. Anybody know where I should start looking? Stuck open Thermostat? some temp sensor??

2001 Ford F150 Supercrew 4x4 4.6L , 83K miles.

Thanks.

 

MachineMan, I'm looking at my service manual and the dtc chart the first question it ask's is "With CHT SENSOR" OR "With ECT SENSOR"?

 

with CHT Sensor - DL110 DTC P0125: CHECK ENGINE COOLANT LEVEL
Diagnostic Trouble Code (DTC) P0125 indicates the CHT sensor has not achieved the required temperature level to enter closed loop operating conditions within a specified amount of time after starting engine. This DTC will light the MIL.

Possible causes:

Insufficient warm up time.
Leaky or stuck open thermostat.
Low engine coolant level.
Malfunctioning CHT sensor.
WARNING: TO AVOID PERSONAL INJURY, DO NOT UNSCREW THE COOLANT PRESSURE RELIEF CAP WHILE THE ENGINE IS OPERATING OR HOT. THE COOLING SYSTEM IS UNDER PRESSURE; STREAM AND HOT LIQUID CAN COME OUT FORCEFULLY WHEN THE CAP IS LOOSENDED SLIGHTLY.

Check engine coolant level.
Is the engine coolant level fill correct?

 

DA80 P0116: CHECK TEMPERATURE SENSOR RESISTANCE WITH ENGINE OFF
Note: Verify that engine temperature is at ambient room temperature before continuing with this test. A soak period of 6 hours may be required. Refer to Diagnostic Trouble Code (DTC) Descriptions , in Section 4 for information concerning P0116.

Key on, engine off.
Disconnect ECT sensor.
Measure ECT sensor resistance. Refer to the chart at the beginning of this Pinpoint Test for resistance specifications.
Is resistance within specification?
Yes No
GO to DA81 . REPLACE suspect sensor.

 

Cool... First thing I will check is the coolant level and if the thermostat is stuck open. What does CHT and ECT stand for? I assume they are resistive temp sensors located somewhere.

Thanks.

 

ECT engine coolant temperature sensor and CHT - Cylinder Head Temperature (CHT) Sensor

 

The 2001 4.6 uses the CHT sensor. There is no ECT sensor on this vehicle.

Does your in-dash TEMP guage read lower than normal, does is show a delay in reaching normal range, etc....

Steve

 

Thanks Steve,
I missed the 4.6L info. MachineMan, let me know, the troubleshooting part of the shop CD has a whole bunch of stuff to check with if this works then try this if it fails try this etc.

MP

 

The temp guage only reached about 25% after 20min of driving. Sounds like the thermostat is stuck open. The coolant needs flushing anyway so I will change it this weekend.

 

A good plan with a high liklihood of a sucessful outcome.

Steve

 

MachineMan, let us know how that turns out, good luck with it

 

Update: I changed the thermostast and its been over a week now. The temp gauge reads dead center and no more "engine service soon" light. Looks like the problem is fixed.

Although the thermostat I took out was in great shape and closed. Maybe the spring was getting weak...

Thanks.

 

MachineMan, Glad to hear that, how much work was it to remove the thermostat?

 

Easiest Thermostat I've ever changed. I had to remove the power steering reservoir bracket and then take the 2 thermostat bolts out. No need to remove the water hose from teh housing. Of course I drained the coolant first. The easy part was the o-ring gasket. No scrapping old gaskets and using RTV.