DTC P0125

The CTS- coolant temperature sensor is indicating to the ECM-Electronic
control module that the engine has not reached proper operating temperature
or the threshold point where the ECM switches from open loop to closed loop
operation.
In open loop the ECM controls various engine functions such as fuel mixture
and engine timing using pre-programmed parameters that are stored in the
PROM- programmable read only memory.
After the engine reaches proper operating temp and all the sensors are
operating correctly
then the ECM switches to closed loop operation and begins receiving data
inputs from various engine control sensors such as TPS-throttle position
sensor, MAP-manifold absolute pressure, MAF-mass air flow, CTS,AIT-air
intake temp., etc etc etc
In a nutshell either the engine is running too cool or the CTS is faulting
causing the ECM to operate in closed loop or (limp home mode) on the early
C3-computer command control systems where i began learning EFI and computer
controlled engines.
You've got to change your way of thinking when dealing with these systems,
sometimes i grab a beer and watch the Disney movie "Tron" when they start
testing my patience.
--
Mad-Dog
'79 Chevy K-10
Slightly modified
http://mad-dog16.tripod.com/

Thanks,

I forgot to mention that the 4x4 is a 1997 Silverado with a 5.7l F1 V8
engine with 125K miles on the odometer.

Ed
...
The CTS- coolant temperature sensor is indicating to the ECM-Electronic
control module that the engine has not reached proper operating temperature
or the threshold point where the ECM switches from open loop to closed loop
operation.
In open loop the ECM controls various engine functions such as fuel mixture
and engine timing using pre-programmed parameters that are stored in the
PROM- programmable read only memory.
After the engine reaches proper operating temp and all the sensors are
operating correctly
then the ECM switches to closed loop operation and begins receiving data
inputs from various engine control sensors such as TPS-throttle position
sensor, MAP-manifold absolute pressure, MAF-mass air flow, CTS,AIT-air
intake temp., etc etc etc
In a nutshell either the engine is running too cool or the CTS is faulting
causing the ECM to operate in closed loop or (limp home mode) on the early
C3-computer command control systems where i began learning EFI and computer
controlled engines.
You've got to change your way of thinking when dealing with these systems,
sometimes i grab a beer and watch the Disney movie "Tron" when they start
testing my patience.
--
Mad-Dog
'79 Chevy K-10
Slightly modified
http://mad-dog16.tripod.com/

Used my ODB II code reader to troubleshoot a Service Engine Soon light.

It quickly returned the following.

P0125
Insufficient coolant temperature for closed loop fuel control

What does it mean?

try replacing the thermostat

According to your temp gauge, is it running as hot as it usually does or
does it seem to be running cooler?

Doc

The engine is not meeting a minimum operating temperature, Replace your
thermostat also use the 195* stat.

...

His stat might be fine, could be a variety of other things either causing
the engine to run cold or causing the PCM to "think" it's running cold. I'd
do some more simple diagnostics before I started throwing parts at it.

Doc

Doc wrote-
According to your temp gauge, is it running as hot as it usually does or
does it seem to be running cooler?

Can't tell, since the truck belongs to my Navy son who was transferred to
Italy last October, I haven't driven it much until recently. My son told me
to sell the truck since he will be in Naples for the next 3 years. I noticed
the service engine light on when I drove it for about four miles just to
keep it in "shape". I'm not sure how long it has been on. I do know that my
son did not tell me anything about it when he dropped it off at my home.

Ed M.

To all-

I checked the coolant level and it was low. It took about a gallon of
anti-freeze to top it off.
I erased the service engine soon light and drove it for about 6 miles and it
remained off.

Thanks for your help.

Ed
...

You have bigger problemsintake manifold gaskets are likely
leaking which is why the coolant was low. You need to check the oil for
coolant and find that leak ASAP.

Doc

Doc,

Is it a common problem with the Vortec 5700 V8 SFI engine?

Ed
...