fjasper

I've had the intermittent mapped cooling error a couple times in the last few weeks, concurrent with some heavy duty cooling system flushes.

I logged the coolant temperature from cold start through warmup, and it seems to rapidly fluctuate by about 5 degrees. Is this normal, or is it supposed to be steady? FWIW, I didn't get the error on this run.

DOALLAR

Your temp guage should hold firm. Im sure you bled the system for air pockets. You might need to replace Temp sensor.

fjasper

The temp gauge on the dash is very steady.

Using the data logger on VCDS, the temperature reported by the coolant temp sensor (G62, if I remember right, but I could be remembering it wrong) swings by about 5 degrees about twice per second. I'm having a hard time explaining it clearly.

When lunchtime rolls around, I'll grab my laptop and try to post a graph of the data.

DOALLAR

17704 code? Are you over heating? Ok, so the temp gauge fluctuates while warming up. If not your temp sensor - Possibly the thermostat is not opening/closing when it should (dips up/down 5 degrees).

fjasper

I must have killed off more brain cells last weekend than I realized, because describing this issue is kicking my butt. I'll have another go at it.

The car intermittently pitches the 17704 code with MIL. There isn't any overheating. The gauge doesn't show anything abnormal. The needle comes up smoothly to the center and stays there. If not for the MIL, I'd have never tried logging coolant temp with VCDS/Vag-Com, because it behaves totally normal as far as the instruments are concerned.

However, with the VCDS/Vag-Com plugged in and logging temperature, I can see that the coolant temp sensor is sending a signal that fluctuates fairly rapidly in a range of about 5-7 degrees. You can see this in the fuzzy/fat/jagged aqua and yellow line in the plot. I don't know if this is normal or not.

The attached plot begins before engine start and covers my morning drive to work. The dark horizontal line is voltage. The light jagged line at the very bottom of the chart is intake air temp, I believe. The plateau in the middle of the temperature plot corresponds to the heater fan kicking in. It was about 32F/0C outside this morning.

What I'm trying to find out is if this fluctuation in temperature _sensor_ (not temperature gauge) reading is normal or if it should be more of a smooth linear plot, implying that my temperature sensor is the problem.

Basically I'm trying to track down an intermittent code, and I'm being cheap/lazy by seeing if the cloud can figure it out before I start replacing parts.

DOALLAR

The graph looks good, it slopes gradually. Another sure way is to check the temp sensor using a volt meter. Usually when you start your car it should read around 3 volts slowly as the car warms up it will read around
.5-1 volt. Im not sure but maybe you can measure ### block for that.

lovely09

How does the coolant temperature sensor "CTS" work?
The coolant temperature sensor is a thermistor ( a resistor which varies the value of its voltage output in accordance with temperature changes. ). The change in the resistance values will directly affect the voltage signal from the water thermosensor. As the sensor temperature decreases,the resistance values will increase.As the sensor temperature increases,the resistance values will decrease.
The coolant temperature sensor lets the engine control computer know what the engine temperature is by gathering information from the engine coolant temperature.
The most common coolant temperature sensor location is near the thermostat housing sometimes the computer uses the same sensor to operate the temperature gauge in your instrument cluster, depending on the car make and model.

fjasper

I replaced the sensor and now the line is steady and rises in one-degree increments (like the manual says it should) rather than hunting back and forth. A driveability issue went away with installation of the new sensor, too.

fjasper

Same drive to work. New temp sensor that gives a steady output instead of the fluctuating signal from the old sensor.